Source file src/cmd/link/internal/ld/data.go

Documentation: cmd/link/internal/ld

     1  // Derived from Inferno utils/6l/obj.c and utils/6l/span.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/obj.c
     3  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/span.c
     4  //
     5  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     6  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     7  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     8  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     9  //	Portions Copyright © 2004,2006 Bruce Ellis
    10  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    11  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    12  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    13  //
    14  // Permission is hereby granted, free of charge, to any person obtaining a copy
    15  // of this software and associated documentation files (the "Software"), to deal
    16  // in the Software without restriction, including without limitation the rights
    17  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    18  // copies of the Software, and to permit persons to whom the Software is
    19  // furnished to do so, subject to the following conditions:
    20  //
    21  // The above copyright notice and this permission notice shall be included in
    22  // all copies or substantial portions of the Software.
    23  //
    24  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    25  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    26  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    27  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    28  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    29  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    30  // THE SOFTWARE.
    31  
    32  package ld
    33  
    34  import (
    35  	"bytes"
    36  	"cmd/internal/gcprog"
    37  	"cmd/internal/objabi"
    38  	"cmd/internal/sys"
    39  	"cmd/link/internal/loader"
    40  	"cmd/link/internal/loadpe"
    41  	"cmd/link/internal/sym"
    42  	"compress/zlib"
    43  	"debug/elf"
    44  	"encoding/binary"
    45  	"fmt"
    46  	"log"
    47  	"os"
    48  	"sort"
    49  	"strconv"
    50  	"strings"
    51  	"sync"
    52  	"sync/atomic"
    53  )
    54  
    55  // isRuntimeDepPkg reports whether pkg is the runtime package or its dependency.
    56  func isRuntimeDepPkg(pkg string) bool {
    57  	switch pkg {
    58  	case "runtime",
    59  		"sync/atomic",          // runtime may call to sync/atomic, due to go:linkname
    60  		"internal/abi",         // used by reflectcall (and maybe more)
    61  		"internal/bytealg",     // for IndexByte
    62  		"internal/chacha8rand", // for rand
    63  		"internal/cpu":         // for cpu features
    64  		return true
    65  	}
    66  	return strings.HasPrefix(pkg, "runtime/internal/") && !strings.HasSuffix(pkg, "_test")
    67  }
    68  
    69  // Estimate the max size needed to hold any new trampolines created for this function. This
    70  // is used to determine when the section can be split if it becomes too large, to ensure that
    71  // the trampolines are in the same section as the function that uses them.
    72  func maxSizeTrampolines(ctxt *Link, ldr *loader.Loader, s loader.Sym, isTramp bool) uint64 {
    73  	// If thearch.Trampoline is nil, then trampoline support is not available on this arch.
    74  	// A trampoline does not need any dependent trampolines.
    75  	if thearch.Trampoline == nil || isTramp {
    76  		return 0
    77  	}
    78  
    79  	n := uint64(0)
    80  	relocs := ldr.Relocs(s)
    81  	for ri := 0; ri < relocs.Count(); ri++ {
    82  		r := relocs.At(ri)
    83  		if r.Type().IsDirectCallOrJump() {
    84  			n++
    85  		}
    86  	}
    87  
    88  	switch {
    89  	case ctxt.IsARM():
    90  		return n * 20 // Trampolines in ARM range from 3 to 5 instructions.
    91  	case ctxt.IsARM64():
    92  		return n * 12 // Trampolines in ARM64 are 3 instructions.
    93  	case ctxt.IsPPC64():
    94  		return n * 16 // Trampolines in PPC64 are 4 instructions.
    95  	case ctxt.IsRISCV64():
    96  		return n * 8 // Trampolines in RISCV64 are 2 instructions.
    97  	}
    98  	panic("unreachable")
    99  }
   100  
   101  // Detect too-far jumps in function s, and add trampolines if necessary.
   102  // ARM, PPC64, PPC64LE and RISCV64 support trampoline insertion for internal
   103  // and external linking. On PPC64 and PPC64LE the text sections might be split
   104  // but will still insert trampolines where necessary.
   105  func trampoline(ctxt *Link, s loader.Sym) {
   106  	if thearch.Trampoline == nil {
   107  		return // no need or no support of trampolines on this arch
   108  	}
   109  
   110  	ldr := ctxt.loader
   111  	relocs := ldr.Relocs(s)
   112  	for ri := 0; ri < relocs.Count(); ri++ {
   113  		r := relocs.At(ri)
   114  		rt := r.Type()
   115  		if !rt.IsDirectCallOrJump() && !isPLTCall(rt) {
   116  			continue
   117  		}
   118  		rs := r.Sym()
   119  		if !ldr.AttrReachable(rs) || ldr.SymType(rs) == sym.Sxxx {
   120  			continue // something is wrong. skip it here and we'll emit a better error later
   121  		}
   122  
   123  		if ldr.SymValue(rs) == 0 && ldr.SymType(rs) != sym.SDYNIMPORT && ldr.SymType(rs) != sym.SUNDEFEXT {
   124  			// Symbols in the same package are laid out together.
   125  			// Except that if SymPkg(s) == "", it is a host object symbol
   126  			// which may call an external symbol via PLT.
   127  			if ldr.SymPkg(s) != "" && ldr.SymPkg(rs) == ldr.SymPkg(s) {
   128  				// RISC-V is only able to reach +/-1MiB via a JAL instruction.
   129  				// We need to generate a trampoline when an address is
   130  				// currently unknown.
   131  				if !ctxt.Target.IsRISCV64() {
   132  					continue
   133  				}
   134  			}
   135  			// Runtime packages are laid out together.
   136  			if isRuntimeDepPkg(ldr.SymPkg(s)) && isRuntimeDepPkg(ldr.SymPkg(rs)) {
   137  				continue
   138  			}
   139  		}
   140  		thearch.Trampoline(ctxt, ldr, ri, rs, s)
   141  	}
   142  }
   143  
   144  // whether rt is a (host object) relocation that will be turned into
   145  // a call to PLT.
   146  func isPLTCall(rt objabi.RelocType) bool {
   147  	const pcrel = 1
   148  	switch rt {
   149  	// ARM64
   150  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_AARCH64_CALL26),
   151  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_AARCH64_JUMP26),
   152  		objabi.MachoRelocOffset + MACHO_ARM64_RELOC_BRANCH26*2 + pcrel:
   153  		return true
   154  
   155  	// ARM
   156  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_CALL),
   157  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_PC24),
   158  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_JUMP24):
   159  		return true
   160  	}
   161  	// TODO: other architectures.
   162  	return false
   163  }
   164  
   165  // FoldSubSymbolOffset computes the offset of symbol s to its top-level outer
   166  // symbol. Returns the top-level symbol and the offset.
   167  // This is used in generating external relocations.
   168  func FoldSubSymbolOffset(ldr *loader.Loader, s loader.Sym) (loader.Sym, int64) {
   169  	outer := ldr.OuterSym(s)
   170  	off := int64(0)
   171  	if outer != 0 {
   172  		off += ldr.SymValue(s) - ldr.SymValue(outer)
   173  		s = outer
   174  	}
   175  	return s, off
   176  }
   177  
   178  // relocsym resolve relocations in "s", updating the symbol's content
   179  // in "P".
   180  // The main loop walks through the list of relocations attached to "s"
   181  // and resolves them where applicable. Relocations are often
   182  // architecture-specific, requiring calls into the 'archreloc' and/or
   183  // 'archrelocvariant' functions for the architecture. When external
   184  // linking is in effect, it may not be  possible to completely resolve
   185  // the address/offset for a symbol, in which case the goal is to lay
   186  // the groundwork for turning a given relocation into an external reloc
   187  // (to be applied by the external linker). For more on how relocations
   188  // work in general, see
   189  //
   190  //	"Linkers and Loaders", by John R. Levine (Morgan Kaufmann, 1999), ch. 7
   191  //
   192  // This is a performance-critical function for the linker; be careful
   193  // to avoid introducing unnecessary allocations in the main loop.
   194  func (st *relocSymState) relocsym(s loader.Sym, P []byte) {
   195  	ldr := st.ldr
   196  	relocs := ldr.Relocs(s)
   197  	if relocs.Count() == 0 {
   198  		return
   199  	}
   200  	target := st.target
   201  	syms := st.syms
   202  	nExtReloc := 0 // number of external relocations
   203  	for ri := 0; ri < relocs.Count(); ri++ {
   204  		r := relocs.At(ri)
   205  		off := r.Off()
   206  		siz := int32(r.Siz())
   207  		rs := r.Sym()
   208  		rt := r.Type()
   209  		weak := r.Weak()
   210  		if off < 0 || off+siz > int32(len(P)) {
   211  			rname := ""
   212  			if rs != 0 {
   213  				rname = ldr.SymName(rs)
   214  			}
   215  			st.err.Errorf(s, "invalid relocation %s: %d+%d not in [%d,%d)", rname, off, siz, 0, len(P))
   216  			continue
   217  		}
   218  		if siz == 0 { // informational relocation - no work to do
   219  			continue
   220  		}
   221  
   222  		var rst sym.SymKind
   223  		if rs != 0 {
   224  			rst = ldr.SymType(rs)
   225  		}
   226  
   227  		if rs != 0 && (rst == sym.Sxxx || rst == sym.SXREF) {
   228  			// When putting the runtime but not main into a shared library
   229  			// these symbols are undefined and that's OK.
   230  			if target.IsShared() || target.IsPlugin() {
   231  				if ldr.SymName(rs) == "main.main" || (!target.IsPlugin() && ldr.SymName(rs) == "main..inittask") {
   232  					sb := ldr.MakeSymbolUpdater(rs)
   233  					sb.SetType(sym.SDYNIMPORT)
   234  				} else if strings.HasPrefix(ldr.SymName(rs), "go:info.") {
   235  					// Skip go.info symbols. They are only needed to communicate
   236  					// DWARF info between the compiler and linker.
   237  					continue
   238  				}
   239  			} else if target.IsPPC64() && ldr.SymName(rs) == ".TOC." {
   240  				// TOC symbol doesn't have a type but we do assign a value
   241  				// (see the address pass) and we can resolve it.
   242  				// TODO: give it a type.
   243  			} else {
   244  				st.err.errorUnresolved(ldr, s, rs)
   245  				continue
   246  			}
   247  		}
   248  
   249  		if rt >= objabi.ElfRelocOffset {
   250  			continue
   251  		}
   252  
   253  		// We need to be able to reference dynimport symbols when linking against
   254  		// shared libraries, and AIX, Darwin, OpenBSD and Solaris always need it.
   255  		if !target.IsAIX() && !target.IsDarwin() && !target.IsSolaris() && !target.IsOpenbsd() && rs != 0 && rst == sym.SDYNIMPORT && !target.IsDynlinkingGo() && !ldr.AttrSubSymbol(rs) {
   256  			if !(target.IsPPC64() && target.IsExternal() && ldr.SymName(rs) == ".TOC.") {
   257  				st.err.Errorf(s, "unhandled relocation for %s (type %d (%s) rtype %d (%s))", ldr.SymName(rs), rst, rst, rt, sym.RelocName(target.Arch, rt))
   258  			}
   259  		}
   260  		if rs != 0 && rst != sym.STLSBSS && !weak && rt != objabi.R_METHODOFF && !ldr.AttrReachable(rs) {
   261  			st.err.Errorf(s, "unreachable sym in relocation: %s", ldr.SymName(rs))
   262  		}
   263  
   264  		var rv sym.RelocVariant
   265  		if target.IsPPC64() || target.IsS390X() {
   266  			rv = ldr.RelocVariant(s, ri)
   267  		}
   268  
   269  		// TODO(mundaym): remove this special case - see issue 14218.
   270  		if target.IsS390X() {
   271  			switch rt {
   272  			case objabi.R_PCRELDBL:
   273  				rt = objabi.R_PCREL
   274  				rv = sym.RV_390_DBL
   275  			case objabi.R_CALL:
   276  				rv = sym.RV_390_DBL
   277  			}
   278  		}
   279  
   280  		var o int64
   281  		switch rt {
   282  		default:
   283  			switch siz {
   284  			default:
   285  				st.err.Errorf(s, "bad reloc size %#x for %s", uint32(siz), ldr.SymName(rs))
   286  			case 1:
   287  				o = int64(P[off])
   288  			case 2:
   289  				o = int64(target.Arch.ByteOrder.Uint16(P[off:]))
   290  			case 4:
   291  				o = int64(target.Arch.ByteOrder.Uint32(P[off:]))
   292  			case 8:
   293  				o = int64(target.Arch.ByteOrder.Uint64(P[off:]))
   294  			}
   295  			out, n, ok := thearch.Archreloc(target, ldr, syms, r, s, o)
   296  			if target.IsExternal() {
   297  				nExtReloc += n
   298  			}
   299  			if ok {
   300  				o = out
   301  			} else {
   302  				st.err.Errorf(s, "unknown reloc to %v: %d (%s)", ldr.SymName(rs), rt, sym.RelocName(target.Arch, rt))
   303  			}
   304  		case objabi.R_TLS_LE:
   305  			if target.IsExternal() && target.IsElf() {
   306  				nExtReloc++
   307  				o = 0
   308  				if !target.IsAMD64() {
   309  					o = r.Add()
   310  				}
   311  				break
   312  			}
   313  
   314  			if target.IsElf() && target.IsARM() {
   315  				// On ELF ARM, the thread pointer is 8 bytes before
   316  				// the start of the thread-local data block, so add 8
   317  				// to the actual TLS offset (r->sym->value).
   318  				// This 8 seems to be a fundamental constant of
   319  				// ELF on ARM (or maybe Glibc on ARM); it is not
   320  				// related to the fact that our own TLS storage happens
   321  				// to take up 8 bytes.
   322  				o = 8 + ldr.SymValue(rs)
   323  			} else if target.IsElf() || target.IsPlan9() || target.IsDarwin() {
   324  				o = int64(syms.Tlsoffset) + r.Add()
   325  			} else if target.IsWindows() {
   326  				o = r.Add()
   327  			} else {
   328  				log.Fatalf("unexpected R_TLS_LE relocation for %v", target.HeadType)
   329  			}
   330  		case objabi.R_TLS_IE:
   331  			if target.IsExternal() && target.IsElf() {
   332  				nExtReloc++
   333  				o = 0
   334  				if !target.IsAMD64() {
   335  					o = r.Add()
   336  				}
   337  				if target.Is386() {
   338  					nExtReloc++ // need two ELF relocations on 386, see ../x86/asm.go:elfreloc1
   339  				}
   340  				break
   341  			}
   342  			if target.IsPIE() && target.IsElf() {
   343  				// We are linking the final executable, so we
   344  				// can optimize any TLS IE relocation to LE.
   345  				if thearch.TLSIEtoLE == nil {
   346  					log.Fatalf("internal linking of TLS IE not supported on %v", target.Arch.Family)
   347  				}
   348  				thearch.TLSIEtoLE(P, int(off), int(siz))
   349  				o = int64(syms.Tlsoffset)
   350  			} else {
   351  				log.Fatalf("cannot handle R_TLS_IE (sym %s) when linking internally", ldr.SymName(s))
   352  			}
   353  		case objabi.R_ADDR, objabi.R_PEIMAGEOFF:
   354  			if weak && !ldr.AttrReachable(rs) {
   355  				// Redirect it to runtime.unreachableMethod, which will throw if called.
   356  				rs = syms.unreachableMethod
   357  			}
   358  			if target.IsExternal() {
   359  				nExtReloc++
   360  
   361  				// set up addend for eventual relocation via outer symbol.
   362  				rs := rs
   363  				rs, off := FoldSubSymbolOffset(ldr, rs)
   364  				xadd := r.Add() + off
   365  				rst := ldr.SymType(rs)
   366  				if rst != sym.SHOSTOBJ && rst != sym.SDYNIMPORT && rst != sym.SUNDEFEXT && ldr.SymSect(rs) == nil {
   367  					st.err.Errorf(s, "missing section for relocation target %s", ldr.SymName(rs))
   368  				}
   369  
   370  				o = xadd
   371  				if target.IsElf() {
   372  					if target.IsAMD64() {
   373  						o = 0
   374  					}
   375  				} else if target.IsDarwin() {
   376  					if ldr.SymType(s).IsDWARF() {
   377  						// We generally use symbol-targeted relocations.
   378  						// DWARF tools seem to only handle section-targeted relocations,
   379  						// so generate section-targeted relocations in DWARF sections.
   380  						// See also machoreloc1.
   381  						o += ldr.SymValue(rs)
   382  					}
   383  				} else if target.IsWindows() {
   384  					// nothing to do
   385  				} else if target.IsAIX() {
   386  					o = ldr.SymValue(rs) + xadd
   387  				} else {
   388  					st.err.Errorf(s, "unhandled pcrel relocation to %s on %v", ldr.SymName(rs), target.HeadType)
   389  				}
   390  
   391  				break
   392  			}
   393  
   394  			// On AIX, a second relocation must be done by the loader,
   395  			// as section addresses can change once loaded.
   396  			// The "default" symbol address is still needed by the loader so
   397  			// the current relocation can't be skipped.
   398  			if target.IsAIX() && rst != sym.SDYNIMPORT {
   399  				// It's not possible to make a loader relocation in a
   400  				// symbol which is not inside .data section.
   401  				// FIXME: It should be forbidden to have R_ADDR from a
   402  				// symbol which isn't in .data. However, as .text has the
   403  				// same address once loaded, this is possible.
   404  				if ldr.SymSect(s).Seg == &Segdata {
   405  					Xcoffadddynrel(target, ldr, syms, s, r, ri)
   406  				}
   407  			}
   408  
   409  			o = ldr.SymValue(rs) + r.Add()
   410  			if rt == objabi.R_PEIMAGEOFF {
   411  				// The R_PEIMAGEOFF offset is a RVA, so subtract
   412  				// the base address for the executable.
   413  				o -= PEBASE
   414  			}
   415  
   416  			// On amd64, 4-byte offsets will be sign-extended, so it is impossible to
   417  			// access more than 2GB of static data; fail at link time is better than
   418  			// fail at runtime. See https://golang.org/issue/7980.
   419  			// Instead of special casing only amd64, we treat this as an error on all
   420  			// 64-bit architectures so as to be future-proof.
   421  			if int32(o) < 0 && target.Arch.PtrSize > 4 && siz == 4 {
   422  				st.err.Errorf(s, "non-pc-relative relocation address for %s is too big: %#x (%#x + %#x)", ldr.SymName(rs), uint64(o), ldr.SymValue(rs), r.Add())
   423  				errorexit()
   424  			}
   425  		case objabi.R_DWARFSECREF:
   426  			if ldr.SymSect(rs) == nil {
   427  				st.err.Errorf(s, "missing DWARF section for relocation target %s", ldr.SymName(rs))
   428  			}
   429  
   430  			if target.IsExternal() {
   431  				// On most platforms, the external linker needs to adjust DWARF references
   432  				// as it combines DWARF sections. However, on Darwin, dsymutil does the
   433  				// DWARF linking, and it understands how to follow section offsets.
   434  				// Leaving in the relocation records confuses it (see
   435  				// https://golang.org/issue/22068) so drop them for Darwin.
   436  				if !target.IsDarwin() {
   437  					nExtReloc++
   438  				}
   439  
   440  				xadd := r.Add() + ldr.SymValue(rs) - int64(ldr.SymSect(rs).Vaddr)
   441  
   442  				o = xadd
   443  				if target.IsElf() && target.IsAMD64() {
   444  					o = 0
   445  				}
   446  				break
   447  			}
   448  			o = ldr.SymValue(rs) + r.Add() - int64(ldr.SymSect(rs).Vaddr)
   449  		case objabi.R_METHODOFF:
   450  			if !ldr.AttrReachable(rs) {
   451  				// Set it to a sentinel value. The runtime knows this is not pointing to
   452  				// anything valid.
   453  				o = -1
   454  				break
   455  			}
   456  			fallthrough
   457  		case objabi.R_ADDROFF:
   458  			if weak && !ldr.AttrReachable(rs) {
   459  				continue
   460  			}
   461  			sect := ldr.SymSect(rs)
   462  			if sect == nil {
   463  				if rst == sym.SDYNIMPORT {
   464  					st.err.Errorf(s, "cannot target DYNIMPORT sym in section-relative reloc: %s", ldr.SymName(rs))
   465  				} else if rst == sym.SUNDEFEXT {
   466  					st.err.Errorf(s, "undefined symbol in relocation: %s", ldr.SymName(rs))
   467  				} else {
   468  					st.err.Errorf(s, "missing section for relocation target %s", ldr.SymName(rs))
   469  				}
   470  				continue
   471  			}
   472  
   473  			// The method offset tables using this relocation expect the offset to be relative
   474  			// to the start of the first text section, even if there are multiple.
   475  			if sect.Name == ".text" {
   476  				o = ldr.SymValue(rs) - int64(Segtext.Sections[0].Vaddr) + r.Add()
   477  			} else {
   478  				o = ldr.SymValue(rs) - int64(ldr.SymSect(rs).Vaddr) + r.Add()
   479  			}
   480  
   481  		case objabi.R_ADDRCUOFF:
   482  			// debug_range and debug_loc elements use this relocation type to get an
   483  			// offset from the start of the compile unit.
   484  			o = ldr.SymValue(rs) + r.Add() - ldr.SymValue(loader.Sym(ldr.SymUnit(rs).Textp[0]))
   485  
   486  		// r.Sym() can be 0 when CALL $(constant) is transformed from absolute PC to relative PC call.
   487  		case objabi.R_GOTPCREL:
   488  			if target.IsDynlinkingGo() && target.IsDarwin() && rs != 0 {
   489  				nExtReloc++
   490  				o = r.Add()
   491  				break
   492  			}
   493  			if target.Is386() && target.IsExternal() && target.IsELF {
   494  				nExtReloc++ // need two ELF relocations on 386, see ../x86/asm.go:elfreloc1
   495  			}
   496  			fallthrough
   497  		case objabi.R_CALL, objabi.R_PCREL:
   498  			if target.IsExternal() && rs != 0 && rst == sym.SUNDEFEXT {
   499  				// pass through to the external linker.
   500  				nExtReloc++
   501  				o = 0
   502  				break
   503  			}
   504  			if target.IsExternal() && rs != 0 && (ldr.SymSect(rs) != ldr.SymSect(s) || rt == objabi.R_GOTPCREL) {
   505  				nExtReloc++
   506  
   507  				// set up addend for eventual relocation via outer symbol.
   508  				rs := rs
   509  				rs, off := FoldSubSymbolOffset(ldr, rs)
   510  				xadd := r.Add() + off - int64(siz) // relative to address after the relocated chunk
   511  				rst := ldr.SymType(rs)
   512  				if rst != sym.SHOSTOBJ && rst != sym.SDYNIMPORT && ldr.SymSect(rs) == nil {
   513  					st.err.Errorf(s, "missing section for relocation target %s", ldr.SymName(rs))
   514  				}
   515  
   516  				o = xadd
   517  				if target.IsElf() {
   518  					if target.IsAMD64() {
   519  						o = 0
   520  					}
   521  				} else if target.IsDarwin() {
   522  					if rt == objabi.R_CALL {
   523  						if target.IsExternal() && rst == sym.SDYNIMPORT {
   524  							if target.IsAMD64() {
   525  								// AMD64 dynamic relocations are relative to the end of the relocation.
   526  								o += int64(siz)
   527  							}
   528  						} else {
   529  							if rst != sym.SHOSTOBJ {
   530  								o += int64(uint64(ldr.SymValue(rs)) - ldr.SymSect(rs).Vaddr)
   531  							}
   532  							o -= int64(off) // relative to section offset, not symbol
   533  						}
   534  					} else {
   535  						o += int64(siz)
   536  					}
   537  				} else if target.IsWindows() && target.IsAMD64() { // only amd64 needs PCREL
   538  					// PE/COFF's PC32 relocation uses the address after the relocated
   539  					// bytes as the base. Compensate by skewing the addend.
   540  					o += int64(siz)
   541  				} else {
   542  					st.err.Errorf(s, "unhandled pcrel relocation to %s on %v", ldr.SymName(rs), target.HeadType)
   543  				}
   544  
   545  				break
   546  			}
   547  
   548  			o = 0
   549  			if rs != 0 {
   550  				o = ldr.SymValue(rs)
   551  			}
   552  
   553  			o += r.Add() - (ldr.SymValue(s) + int64(off) + int64(siz))
   554  		case objabi.R_SIZE:
   555  			o = ldr.SymSize(rs) + r.Add()
   556  
   557  		case objabi.R_XCOFFREF:
   558  			if !target.IsAIX() {
   559  				st.err.Errorf(s, "find XCOFF R_REF on non-XCOFF files")
   560  			}
   561  			if !target.IsExternal() {
   562  				st.err.Errorf(s, "find XCOFF R_REF with internal linking")
   563  			}
   564  			nExtReloc++
   565  			continue
   566  
   567  		case objabi.R_DWARFFILEREF:
   568  			// We don't renumber files in dwarf.go:writelines anymore.
   569  			continue
   570  
   571  		case objabi.R_CONST:
   572  			o = r.Add()
   573  
   574  		case objabi.R_GOTOFF:
   575  			o = ldr.SymValue(rs) + r.Add() - ldr.SymValue(syms.GOT)
   576  		}
   577  
   578  		if target.IsPPC64() || target.IsS390X() {
   579  			if rv != sym.RV_NONE {
   580  				o = thearch.Archrelocvariant(target, ldr, r, rv, s, o, P)
   581  			}
   582  		}
   583  
   584  		switch siz {
   585  		default:
   586  			st.err.Errorf(s, "bad reloc size %#x for %s", uint32(siz), ldr.SymName(rs))
   587  		case 1:
   588  			P[off] = byte(int8(o))
   589  		case 2:
   590  			if (rt == objabi.R_PCREL || rt == objabi.R_CALL) && o != int64(int16(o)) {
   591  				st.err.Errorf(s, "pc-relative relocation address for %s is too big: %#x", ldr.SymName(rs), o)
   592  			} else if o != int64(int16(o)) && o != int64(uint16(o)) {
   593  				st.err.Errorf(s, "non-pc-relative relocation address for %s is too big: %#x", ldr.SymName(rs), uint64(o))
   594  			}
   595  			target.Arch.ByteOrder.PutUint16(P[off:], uint16(o))
   596  		case 4:
   597  			if (rt == objabi.R_PCREL || rt == objabi.R_CALL) && o != int64(int32(o)) {
   598  				st.err.Errorf(s, "pc-relative relocation address for %s is too big: %#x", ldr.SymName(rs), o)
   599  			} else if o != int64(int32(o)) && o != int64(uint32(o)) {
   600  				st.err.Errorf(s, "non-pc-relative relocation address for %s is too big: %#x", ldr.SymName(rs), uint64(o))
   601  			}
   602  			target.Arch.ByteOrder.PutUint32(P[off:], uint32(o))
   603  		case 8:
   604  			target.Arch.ByteOrder.PutUint64(P[off:], uint64(o))
   605  		}
   606  	}
   607  	if target.IsExternal() {
   608  		// We'll stream out the external relocations in asmb2 (e.g. elfrelocsect)
   609  		// and we only need the count here.
   610  		atomic.AddUint32(&ldr.SymSect(s).Relcount, uint32(nExtReloc))
   611  	}
   612  }
   613  
   614  // Convert a Go relocation to an external relocation.
   615  func extreloc(ctxt *Link, ldr *loader.Loader, s loader.Sym, r loader.Reloc) (loader.ExtReloc, bool) {
   616  	var rr loader.ExtReloc
   617  	target := &ctxt.Target
   618  	siz := int32(r.Siz())
   619  	if siz == 0 { // informational relocation - no work to do
   620  		return rr, false
   621  	}
   622  
   623  	rt := r.Type()
   624  	if rt >= objabi.ElfRelocOffset {
   625  		return rr, false
   626  	}
   627  	rr.Type = rt
   628  	rr.Size = uint8(siz)
   629  
   630  	// TODO(mundaym): remove this special case - see issue 14218.
   631  	if target.IsS390X() {
   632  		switch rt {
   633  		case objabi.R_PCRELDBL:
   634  			rt = objabi.R_PCREL
   635  		}
   636  	}
   637  
   638  	switch rt {
   639  	default:
   640  		return thearch.Extreloc(target, ldr, r, s)
   641  
   642  	case objabi.R_TLS_LE, objabi.R_TLS_IE:
   643  		if target.IsElf() {
   644  			rs := r.Sym()
   645  			rr.Xsym = rs
   646  			if rr.Xsym == 0 {
   647  				rr.Xsym = ctxt.Tlsg
   648  			}
   649  			rr.Xadd = r.Add()
   650  			break
   651  		}
   652  		return rr, false
   653  
   654  	case objabi.R_ADDR, objabi.R_PEIMAGEOFF:
   655  		// set up addend for eventual relocation via outer symbol.
   656  		rs := r.Sym()
   657  		if r.Weak() && !ldr.AttrReachable(rs) {
   658  			rs = ctxt.ArchSyms.unreachableMethod
   659  		}
   660  		rs, off := FoldSubSymbolOffset(ldr, rs)
   661  		rr.Xadd = r.Add() + off
   662  		rr.Xsym = rs
   663  
   664  	case objabi.R_DWARFSECREF:
   665  		// On most platforms, the external linker needs to adjust DWARF references
   666  		// as it combines DWARF sections. However, on Darwin, dsymutil does the
   667  		// DWARF linking, and it understands how to follow section offsets.
   668  		// Leaving in the relocation records confuses it (see
   669  		// https://golang.org/issue/22068) so drop them for Darwin.
   670  		if target.IsDarwin() {
   671  			return rr, false
   672  		}
   673  		rs := r.Sym()
   674  		rr.Xsym = loader.Sym(ldr.SymSect(rs).Sym)
   675  		rr.Xadd = r.Add() + ldr.SymValue(rs) - int64(ldr.SymSect(rs).Vaddr)
   676  
   677  	// r.Sym() can be 0 when CALL $(constant) is transformed from absolute PC to relative PC call.
   678  	case objabi.R_GOTPCREL, objabi.R_CALL, objabi.R_PCREL:
   679  		rs := r.Sym()
   680  		if rt == objabi.R_GOTPCREL && target.IsDynlinkingGo() && target.IsDarwin() && rs != 0 {
   681  			rr.Xadd = r.Add()
   682  			rr.Xadd -= int64(siz) // relative to address after the relocated chunk
   683  			rr.Xsym = rs
   684  			break
   685  		}
   686  		if rs != 0 && ldr.SymType(rs) == sym.SUNDEFEXT {
   687  			// pass through to the external linker.
   688  			rr.Xadd = 0
   689  			if target.IsElf() {
   690  				rr.Xadd -= int64(siz)
   691  			}
   692  			rr.Xsym = rs
   693  			break
   694  		}
   695  		if rs != 0 && (ldr.SymSect(rs) != ldr.SymSect(s) || rt == objabi.R_GOTPCREL) {
   696  			// set up addend for eventual relocation via outer symbol.
   697  			rs := rs
   698  			rs, off := FoldSubSymbolOffset(ldr, rs)
   699  			rr.Xadd = r.Add() + off
   700  			rr.Xadd -= int64(siz) // relative to address after the relocated chunk
   701  			rr.Xsym = rs
   702  			break
   703  		}
   704  		return rr, false
   705  
   706  	case objabi.R_XCOFFREF:
   707  		return ExtrelocSimple(ldr, r), true
   708  
   709  	// These reloc types don't need external relocations.
   710  	case objabi.R_ADDROFF, objabi.R_METHODOFF, objabi.R_ADDRCUOFF,
   711  		objabi.R_SIZE, objabi.R_CONST, objabi.R_GOTOFF:
   712  		return rr, false
   713  	}
   714  	return rr, true
   715  }
   716  
   717  // ExtrelocSimple creates a simple external relocation from r, with the same
   718  // symbol and addend.
   719  func ExtrelocSimple(ldr *loader.Loader, r loader.Reloc) loader.ExtReloc {
   720  	var rr loader.ExtReloc
   721  	rs := r.Sym()
   722  	rr.Xsym = rs
   723  	rr.Xadd = r.Add()
   724  	rr.Type = r.Type()
   725  	rr.Size = r.Siz()
   726  	return rr
   727  }
   728  
   729  // ExtrelocViaOuterSym creates an external relocation from r targeting the
   730  // outer symbol and folding the subsymbol's offset into the addend.
   731  func ExtrelocViaOuterSym(ldr *loader.Loader, r loader.Reloc, s loader.Sym) loader.ExtReloc {
   732  	// set up addend for eventual relocation via outer symbol.
   733  	var rr loader.ExtReloc
   734  	rs := r.Sym()
   735  	rs, off := FoldSubSymbolOffset(ldr, rs)
   736  	rr.Xadd = r.Add() + off
   737  	rst := ldr.SymType(rs)
   738  	if rst != sym.SHOSTOBJ && rst != sym.SDYNIMPORT && rst != sym.SUNDEFEXT && ldr.SymSect(rs) == nil {
   739  		ldr.Errorf(s, "missing section for %s", ldr.SymName(rs))
   740  	}
   741  	rr.Xsym = rs
   742  	rr.Type = r.Type()
   743  	rr.Size = r.Siz()
   744  	return rr
   745  }
   746  
   747  // relocSymState hold state information needed when making a series of
   748  // successive calls to relocsym(). The items here are invariant
   749  // (meaning that they are set up once initially and then don't change
   750  // during the execution of relocsym), with the exception of a slice
   751  // used to facilitate batch allocation of external relocations. Calls
   752  // to relocsym happen in parallel; the assumption is that each
   753  // parallel thread will have its own state object.
   754  type relocSymState struct {
   755  	target *Target
   756  	ldr    *loader.Loader
   757  	err    *ErrorReporter
   758  	syms   *ArchSyms
   759  }
   760  
   761  // makeRelocSymState creates a relocSymState container object to
   762  // pass to relocsym(). If relocsym() calls happen in parallel,
   763  // each parallel thread should have its own state object.
   764  func (ctxt *Link) makeRelocSymState() *relocSymState {
   765  	return &relocSymState{
   766  		target: &ctxt.Target,
   767  		ldr:    ctxt.loader,
   768  		err:    &ctxt.ErrorReporter,
   769  		syms:   &ctxt.ArchSyms,
   770  	}
   771  }
   772  
   773  // windynrelocsym examines a text symbol 's' and looks for relocations
   774  // from it that correspond to references to symbols defined in DLLs,
   775  // then fixes up those relocations as needed. A reference to a symbol
   776  // XYZ from some DLL will fall into one of two categories: an indirect
   777  // ref via "__imp_XYZ", or a direct ref to "XYZ". Here's an example of
   778  // an indirect ref (this is an excerpt from objdump -ldr):
   779  //
   780  //	     1c1: 48 89 c6                     	movq	%rax, %rsi
   781  //	     1c4: ff 15 00 00 00 00            	callq	*(%rip)
   782  //			00000000000001c6:  IMAGE_REL_AMD64_REL32	__imp__errno
   783  //
   784  // In the assembly above, the code loads up the value of __imp_errno
   785  // and then does an indirect call to that value.
   786  //
   787  // Here is what a direct reference might look like:
   788  //
   789  //	     137: e9 20 06 00 00               	jmp	0x75c <pow+0x75c>
   790  //	     13c: e8 00 00 00 00               	callq	0x141 <pow+0x141>
   791  //			000000000000013d:  IMAGE_REL_AMD64_REL32	_errno
   792  //
   793  // The assembly below dispenses with the import symbol and just makes
   794  // a direct call to _errno.
   795  //
   796  // The code below handles indirect refs by redirecting the target of
   797  // the relocation from "__imp_XYZ" to "XYZ" (since the latter symbol
   798  // is what the Windows loader is expected to resolve). For direct refs
   799  // the call is redirected to a stub, where the stub first loads the
   800  // symbol and then direct an indirect call to that value.
   801  //
   802  // Note that for a given symbol (as above) it is perfectly legal to
   803  // have both direct and indirect references.
   804  func windynrelocsym(ctxt *Link, rel *loader.SymbolBuilder, s loader.Sym) error {
   805  	var su *loader.SymbolBuilder
   806  	relocs := ctxt.loader.Relocs(s)
   807  	for ri := 0; ri < relocs.Count(); ri++ {
   808  		r := relocs.At(ri)
   809  		if r.IsMarker() {
   810  			continue // skip marker relocations
   811  		}
   812  		targ := r.Sym()
   813  		if targ == 0 {
   814  			continue
   815  		}
   816  		if !ctxt.loader.AttrReachable(targ) {
   817  			if r.Weak() {
   818  				continue
   819  			}
   820  			return fmt.Errorf("dynamic relocation to unreachable symbol %s",
   821  				ctxt.loader.SymName(targ))
   822  		}
   823  		tgot := ctxt.loader.SymGot(targ)
   824  		if tgot == loadpe.RedirectToDynImportGotToken {
   825  
   826  			// Consistency check: name should be __imp_X
   827  			sname := ctxt.loader.SymName(targ)
   828  			if !strings.HasPrefix(sname, "__imp_") {
   829  				return fmt.Errorf("internal error in windynrelocsym: redirect GOT token applied to non-import symbol %s", sname)
   830  			}
   831  
   832  			// Locate underlying symbol (which originally had type
   833  			// SDYNIMPORT but has since been retyped to SWINDOWS).
   834  			ds, err := loadpe.LookupBaseFromImport(targ, ctxt.loader, ctxt.Arch)
   835  			if err != nil {
   836  				return err
   837  			}
   838  			dstyp := ctxt.loader.SymType(ds)
   839  			if dstyp != sym.SWINDOWS {
   840  				return fmt.Errorf("internal error in windynrelocsym: underlying sym for %q has wrong type %s", sname, dstyp.String())
   841  			}
   842  
   843  			// Redirect relocation to the dynimport.
   844  			r.SetSym(ds)
   845  			continue
   846  		}
   847  
   848  		tplt := ctxt.loader.SymPlt(targ)
   849  		if tplt == loadpe.CreateImportStubPltToken {
   850  
   851  			// Consistency check: don't want to see both PLT and GOT tokens.
   852  			if tgot != -1 {
   853  				return fmt.Errorf("internal error in windynrelocsym: invalid GOT setting %d for reloc to %s", tgot, ctxt.loader.SymName(targ))
   854  			}
   855  
   856  			// make dynimport JMP table for PE object files.
   857  			tplt := int32(rel.Size())
   858  			ctxt.loader.SetPlt(targ, tplt)
   859  
   860  			if su == nil {
   861  				su = ctxt.loader.MakeSymbolUpdater(s)
   862  			}
   863  			r.SetSym(rel.Sym())
   864  			r.SetAdd(int64(tplt))
   865  
   866  			// jmp *addr
   867  			switch ctxt.Arch.Family {
   868  			default:
   869  				return fmt.Errorf("internal error in windynrelocsym: unsupported arch %v", ctxt.Arch.Family)
   870  			case sys.I386:
   871  				rel.AddUint8(0xff)
   872  				rel.AddUint8(0x25)
   873  				rel.AddAddrPlus(ctxt.Arch, targ, 0)
   874  				rel.AddUint8(0x90)
   875  				rel.AddUint8(0x90)
   876  			case sys.AMD64:
   877  				rel.AddUint8(0xff)
   878  				rel.AddUint8(0x24)
   879  				rel.AddUint8(0x25)
   880  				rel.AddAddrPlus4(ctxt.Arch, targ, 0)
   881  				rel.AddUint8(0x90)
   882  			}
   883  		} else if tplt >= 0 {
   884  			if su == nil {
   885  				su = ctxt.loader.MakeSymbolUpdater(s)
   886  			}
   887  			r.SetSym(rel.Sym())
   888  			r.SetAdd(int64(tplt))
   889  		}
   890  	}
   891  	return nil
   892  }
   893  
   894  // windynrelocsyms generates jump table to C library functions that will be
   895  // added later. windynrelocsyms writes the table into .rel symbol.
   896  func (ctxt *Link) windynrelocsyms() {
   897  	if !(ctxt.IsWindows() && iscgo && ctxt.IsInternal()) {
   898  		return
   899  	}
   900  
   901  	rel := ctxt.loader.CreateSymForUpdate(".rel", 0)
   902  	rel.SetType(sym.STEXT)
   903  
   904  	for _, s := range ctxt.Textp {
   905  		if err := windynrelocsym(ctxt, rel, s); err != nil {
   906  			ctxt.Errorf(s, "%v", err)
   907  		}
   908  	}
   909  
   910  	ctxt.Textp = append(ctxt.Textp, rel.Sym())
   911  }
   912  
   913  func dynrelocsym(ctxt *Link, s loader.Sym) {
   914  	target := &ctxt.Target
   915  	ldr := ctxt.loader
   916  	syms := &ctxt.ArchSyms
   917  	relocs := ldr.Relocs(s)
   918  	for ri := 0; ri < relocs.Count(); ri++ {
   919  		r := relocs.At(ri)
   920  		if r.IsMarker() {
   921  			continue // skip marker relocations
   922  		}
   923  		rSym := r.Sym()
   924  		if r.Weak() && !ldr.AttrReachable(rSym) {
   925  			continue
   926  		}
   927  		if ctxt.BuildMode == BuildModePIE && ctxt.LinkMode == LinkInternal {
   928  			// It's expected that some relocations will be done
   929  			// later by relocsym (R_TLS_LE, R_ADDROFF), so
   930  			// don't worry if Adddynrel returns false.
   931  			thearch.Adddynrel(target, ldr, syms, s, r, ri)
   932  			continue
   933  		}
   934  
   935  		if rSym != 0 && ldr.SymType(rSym) == sym.SDYNIMPORT || r.Type() >= objabi.ElfRelocOffset {
   936  			if rSym != 0 && !ldr.AttrReachable(rSym) {
   937  				ctxt.Errorf(s, "dynamic relocation to unreachable symbol %s", ldr.SymName(rSym))
   938  			}
   939  			if !thearch.Adddynrel(target, ldr, syms, s, r, ri) {
   940  				ctxt.Errorf(s, "unsupported dynamic relocation for symbol %s (type=%d (%s) stype=%d (%s))", ldr.SymName(rSym), r.Type(), sym.RelocName(ctxt.Arch, r.Type()), ldr.SymType(rSym), ldr.SymType(rSym))
   941  			}
   942  		}
   943  	}
   944  }
   945  
   946  func (state *dodataState) dynreloc(ctxt *Link) {
   947  	if ctxt.HeadType == objabi.Hwindows {
   948  		return
   949  	}
   950  	// -d suppresses dynamic loader format, so we may as well not
   951  	// compute these sections or mark their symbols as reachable.
   952  	if *FlagD {
   953  		return
   954  	}
   955  
   956  	for _, s := range ctxt.Textp {
   957  		dynrelocsym(ctxt, s)
   958  	}
   959  	for _, syms := range state.data {
   960  		for _, s := range syms {
   961  			dynrelocsym(ctxt, s)
   962  		}
   963  	}
   964  	if ctxt.IsELF {
   965  		elfdynhash(ctxt)
   966  	}
   967  }
   968  
   969  func CodeblkPad(ctxt *Link, out *OutBuf, addr int64, size int64, pad []byte) {
   970  	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, ctxt.Textp, addr, size, pad)
   971  }
   972  
   973  const blockSize = 1 << 20 // 1MB chunks written at a time.
   974  
   975  // writeBlocks writes a specified chunk of symbols to the output buffer. It
   976  // breaks the write up into ≥blockSize chunks to write them out, and schedules
   977  // as many goroutines as necessary to accomplish this task. This call then
   978  // blocks, waiting on the writes to complete. Note that we use the sem parameter
   979  // to limit the number of concurrent writes taking place.
   980  func writeBlocks(ctxt *Link, out *OutBuf, sem chan int, ldr *loader.Loader, syms []loader.Sym, addr, size int64, pad []byte) {
   981  	for i, s := range syms {
   982  		if ldr.SymValue(s) >= addr && !ldr.AttrSubSymbol(s) {
   983  			syms = syms[i:]
   984  			break
   985  		}
   986  	}
   987  
   988  	var wg sync.WaitGroup
   989  	max, lastAddr, written := int64(blockSize), addr+size, int64(0)
   990  	for addr < lastAddr {
   991  		// Find the last symbol we'd write.
   992  		idx := -1
   993  		for i, s := range syms {
   994  			if ldr.AttrSubSymbol(s) {
   995  				continue
   996  			}
   997  
   998  			// If the next symbol's size would put us out of bounds on the total length,
   999  			// stop looking.
  1000  			end := ldr.SymValue(s) + ldr.SymSize(s)
  1001  			if end > lastAddr {
  1002  				break
  1003  			}
  1004  
  1005  			// We're gonna write this symbol.
  1006  			idx = i
  1007  
  1008  			// If we cross over the max size, we've got enough symbols.
  1009  			if end > addr+max {
  1010  				break
  1011  			}
  1012  		}
  1013  
  1014  		// If we didn't find any symbols to write, we're done here.
  1015  		if idx < 0 {
  1016  			break
  1017  		}
  1018  
  1019  		// Compute the length to write, including padding.
  1020  		// We need to write to the end address (lastAddr), or the next symbol's
  1021  		// start address, whichever comes first. If there is no more symbols,
  1022  		// just write to lastAddr. This ensures we don't leave holes between the
  1023  		// blocks or at the end.
  1024  		length := int64(0)
  1025  		if idx+1 < len(syms) {
  1026  			// Find the next top-level symbol.
  1027  			// Skip over sub symbols so we won't split a container symbol
  1028  			// into two blocks.
  1029  			next := syms[idx+1]
  1030  			for ldr.AttrSubSymbol(next) {
  1031  				idx++
  1032  				next = syms[idx+1]
  1033  			}
  1034  			length = ldr.SymValue(next) - addr
  1035  		}
  1036  		if length == 0 || length > lastAddr-addr {
  1037  			length = lastAddr - addr
  1038  		}
  1039  
  1040  		// Start the block output operator.
  1041  		if o, err := out.View(uint64(out.Offset() + written)); err == nil {
  1042  			sem <- 1
  1043  			wg.Add(1)
  1044  			go func(o *OutBuf, ldr *loader.Loader, syms []loader.Sym, addr, size int64, pad []byte) {
  1045  				writeBlock(ctxt, o, ldr, syms, addr, size, pad)
  1046  				wg.Done()
  1047  				<-sem
  1048  			}(o, ldr, syms, addr, length, pad)
  1049  		} else { // output not mmaped, don't parallelize.
  1050  			writeBlock(ctxt, out, ldr, syms, addr, length, pad)
  1051  		}
  1052  
  1053  		// Prepare for the next loop.
  1054  		if idx != -1 {
  1055  			syms = syms[idx+1:]
  1056  		}
  1057  		written += length
  1058  		addr += length
  1059  	}
  1060  	wg.Wait()
  1061  }
  1062  
  1063  func writeBlock(ctxt *Link, out *OutBuf, ldr *loader.Loader, syms []loader.Sym, addr, size int64, pad []byte) {
  1064  
  1065  	st := ctxt.makeRelocSymState()
  1066  
  1067  	// This doesn't distinguish the memory size from the file
  1068  	// size, and it lays out the file based on Symbol.Value, which
  1069  	// is the virtual address. DWARF compression changes file sizes,
  1070  	// so dwarfcompress will fix this up later if necessary.
  1071  	eaddr := addr + size
  1072  	for _, s := range syms {
  1073  		if ldr.AttrSubSymbol(s) {
  1074  			continue
  1075  		}
  1076  		val := ldr.SymValue(s)
  1077  		if val >= eaddr {
  1078  			break
  1079  		}
  1080  		if val < addr {
  1081  			ldr.Errorf(s, "phase error: addr=%#x but val=%#x sym=%s type=%v sect=%v sect.addr=%#x", addr, val, ldr.SymName(s), ldr.SymType(s), ldr.SymSect(s).Name, ldr.SymSect(s).Vaddr)
  1082  			errorexit()
  1083  		}
  1084  		if addr < val {
  1085  			out.WriteStringPad("", int(val-addr), pad)
  1086  			addr = val
  1087  		}
  1088  		P := out.WriteSym(ldr, s)
  1089  		st.relocsym(s, P)
  1090  		if ldr.IsGeneratedSym(s) {
  1091  			f := ctxt.generatorSyms[s]
  1092  			f(ctxt, s)
  1093  		}
  1094  		addr += int64(len(P))
  1095  		siz := ldr.SymSize(s)
  1096  		if addr < val+siz {
  1097  			out.WriteStringPad("", int(val+siz-addr), pad)
  1098  			addr = val + siz
  1099  		}
  1100  		if addr != val+siz {
  1101  			ldr.Errorf(s, "phase error: addr=%#x value+size=%#x", addr, val+siz)
  1102  			errorexit()
  1103  		}
  1104  		if val+siz >= eaddr {
  1105  			break
  1106  		}
  1107  	}
  1108  
  1109  	if addr < eaddr {
  1110  		out.WriteStringPad("", int(eaddr-addr), pad)
  1111  	}
  1112  }
  1113  
  1114  type writeFn func(*Link, *OutBuf, int64, int64)
  1115  
  1116  // writeParallel handles scheduling parallel execution of data write functions.
  1117  func writeParallel(wg *sync.WaitGroup, fn writeFn, ctxt *Link, seek, vaddr, length uint64) {
  1118  	if out, err := ctxt.Out.View(seek); err != nil {
  1119  		ctxt.Out.SeekSet(int64(seek))
  1120  		fn(ctxt, ctxt.Out, int64(vaddr), int64(length))
  1121  	} else {
  1122  		wg.Add(1)
  1123  		go func() {
  1124  			defer wg.Done()
  1125  			fn(ctxt, out, int64(vaddr), int64(length))
  1126  		}()
  1127  	}
  1128  }
  1129  
  1130  func datblk(ctxt *Link, out *OutBuf, addr, size int64) {
  1131  	writeDatblkToOutBuf(ctxt, out, addr, size)
  1132  }
  1133  
  1134  // Used only on Wasm for now.
  1135  func DatblkBytes(ctxt *Link, addr int64, size int64) []byte {
  1136  	buf := make([]byte, size)
  1137  	out := &OutBuf{heap: buf}
  1138  	writeDatblkToOutBuf(ctxt, out, addr, size)
  1139  	return buf
  1140  }
  1141  
  1142  func writeDatblkToOutBuf(ctxt *Link, out *OutBuf, addr int64, size int64) {
  1143  	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, ctxt.datap, addr, size, zeros[:])
  1144  }
  1145  
  1146  func dwarfblk(ctxt *Link, out *OutBuf, addr int64, size int64) {
  1147  	// Concatenate the section symbol lists into a single list to pass
  1148  	// to writeBlocks.
  1149  	//
  1150  	// NB: ideally we would do a separate writeBlocks call for each
  1151  	// section, but this would run the risk of undoing any file offset
  1152  	// adjustments made during layout.
  1153  	n := 0
  1154  	for i := range dwarfp {
  1155  		n += len(dwarfp[i].syms)
  1156  	}
  1157  	syms := make([]loader.Sym, 0, n)
  1158  	for i := range dwarfp {
  1159  		syms = append(syms, dwarfp[i].syms...)
  1160  	}
  1161  	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, syms, addr, size, zeros[:])
  1162  }
  1163  
  1164  func pdatablk(ctxt *Link, out *OutBuf, addr int64, size int64) {
  1165  	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, sehp.pdata, addr, size, zeros[:])
  1166  }
  1167  
  1168  func xdatablk(ctxt *Link, out *OutBuf, addr int64, size int64) {
  1169  	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, sehp.xdata, addr, size, zeros[:])
  1170  }
  1171  
  1172  var covCounterDataStartOff, covCounterDataLen uint64
  1173  
  1174  var zeros [512]byte
  1175  
  1176  var (
  1177  	strdata  = make(map[string]string)
  1178  	strnames []string
  1179  )
  1180  
  1181  func addstrdata1(ctxt *Link, arg string) {
  1182  	eq := strings.Index(arg, "=")
  1183  	dot := strings.LastIndex(arg[:eq+1], ".")
  1184  	if eq < 0 || dot < 0 {
  1185  		Exitf("-X flag requires argument of the form importpath.name=value")
  1186  	}
  1187  	pkg := arg[:dot]
  1188  	if ctxt.BuildMode == BuildModePlugin && pkg == "main" {
  1189  		pkg = *flagPluginPath
  1190  	}
  1191  	pkg = objabi.PathToPrefix(pkg)
  1192  	name := pkg + arg[dot:eq]
  1193  	value := arg[eq+1:]
  1194  	if _, ok := strdata[name]; !ok {
  1195  		strnames = append(strnames, name)
  1196  	}
  1197  	strdata[name] = value
  1198  }
  1199  
  1200  // addstrdata sets the initial value of the string variable name to value.
  1201  func addstrdata(arch *sys.Arch, l *loader.Loader, name, value string) {
  1202  	s := l.Lookup(name, 0)
  1203  	if s == 0 {
  1204  		return
  1205  	}
  1206  	if goType := l.SymGoType(s); goType == 0 {
  1207  		return
  1208  	} else if typeName := l.SymName(goType); typeName != "type:string" {
  1209  		Errorf(nil, "%s: cannot set with -X: not a var of type string (%s)", name, typeName)
  1210  		return
  1211  	}
  1212  	if !l.AttrReachable(s) {
  1213  		return // don't bother setting unreachable variable
  1214  	}
  1215  	bld := l.MakeSymbolUpdater(s)
  1216  	if bld.Type() == sym.SBSS {
  1217  		bld.SetType(sym.SDATA)
  1218  	}
  1219  
  1220  	p := fmt.Sprintf("%s.str", name)
  1221  	sbld := l.CreateSymForUpdate(p, 0)
  1222  	sbld.Addstring(value)
  1223  	sbld.SetType(sym.SRODATA)
  1224  
  1225  	// Don't reset the variable's size. String variable usually has size of
  1226  	// 2*PtrSize, but in ASAN build it can be larger due to red zone.
  1227  	// (See issue 56175.)
  1228  	bld.SetData(make([]byte, arch.PtrSize*2))
  1229  	bld.SetReadOnly(false)
  1230  	bld.ResetRelocs()
  1231  	bld.SetAddrPlus(arch, 0, sbld.Sym(), 0)
  1232  	bld.SetUint(arch, int64(arch.PtrSize), uint64(len(value)))
  1233  }
  1234  
  1235  func (ctxt *Link) dostrdata() {
  1236  	for _, name := range strnames {
  1237  		addstrdata(ctxt.Arch, ctxt.loader, name, strdata[name])
  1238  	}
  1239  }
  1240  
  1241  // addgostring adds str, as a Go string value, to s. symname is the name of the
  1242  // symbol used to define the string data and must be unique per linked object.
  1243  func addgostring(ctxt *Link, ldr *loader.Loader, s *loader.SymbolBuilder, symname, str string) {
  1244  	sdata := ldr.CreateSymForUpdate(symname, 0)
  1245  	if sdata.Type() != sym.Sxxx {
  1246  		ctxt.Errorf(s.Sym(), "duplicate symname in addgostring: %s", symname)
  1247  	}
  1248  	sdata.SetLocal(true)
  1249  	sdata.SetType(sym.SRODATA)
  1250  	sdata.SetSize(int64(len(str)))
  1251  	sdata.SetData([]byte(str))
  1252  	s.AddAddr(ctxt.Arch, sdata.Sym())
  1253  	s.AddUint(ctxt.Arch, uint64(len(str)))
  1254  }
  1255  
  1256  func addinitarrdata(ctxt *Link, ldr *loader.Loader, s loader.Sym) {
  1257  	p := ldr.SymName(s) + ".ptr"
  1258  	sp := ldr.CreateSymForUpdate(p, 0)
  1259  	sp.SetType(sym.SINITARR)
  1260  	sp.SetSize(0)
  1261  	sp.SetDuplicateOK(true)
  1262  	sp.AddAddr(ctxt.Arch, s)
  1263  }
  1264  
  1265  // symalign returns the required alignment for the given symbol s.
  1266  func symalign(ldr *loader.Loader, s loader.Sym) int32 {
  1267  	min := int32(thearch.Minalign)
  1268  	align := ldr.SymAlign(s)
  1269  	if align >= min {
  1270  		return align
  1271  	} else if align != 0 {
  1272  		return min
  1273  	}
  1274  	align = int32(thearch.Maxalign)
  1275  	ssz := ldr.SymSize(s)
  1276  	for int64(align) > ssz && align > min {
  1277  		align >>= 1
  1278  	}
  1279  	ldr.SetSymAlign(s, align)
  1280  	return align
  1281  }
  1282  
  1283  func aligndatsize(state *dodataState, datsize int64, s loader.Sym) int64 {
  1284  	return Rnd(datsize, int64(symalign(state.ctxt.loader, s)))
  1285  }
  1286  
  1287  const debugGCProg = false
  1288  
  1289  type GCProg struct {
  1290  	ctxt *Link
  1291  	sym  *loader.SymbolBuilder
  1292  	w    gcprog.Writer
  1293  }
  1294  
  1295  func (p *GCProg) Init(ctxt *Link, name string) {
  1296  	p.ctxt = ctxt
  1297  	p.sym = ctxt.loader.CreateSymForUpdate(name, 0)
  1298  	p.w.Init(p.writeByte())
  1299  	if debugGCProg {
  1300  		fmt.Fprintf(os.Stderr, "ld: start GCProg %s\n", name)
  1301  		p.w.Debug(os.Stderr)
  1302  	}
  1303  }
  1304  
  1305  func (p *GCProg) writeByte() func(x byte) {
  1306  	return func(x byte) {
  1307  		p.sym.AddUint8(x)
  1308  	}
  1309  }
  1310  
  1311  func (p *GCProg) End(size int64) {
  1312  	p.w.ZeroUntil(size / int64(p.ctxt.Arch.PtrSize))
  1313  	p.w.End()
  1314  	if debugGCProg {
  1315  		fmt.Fprintf(os.Stderr, "ld: end GCProg\n")
  1316  	}
  1317  }
  1318  
  1319  func (p *GCProg) AddSym(s loader.Sym) {
  1320  	ldr := p.ctxt.loader
  1321  	typ := ldr.SymGoType(s)
  1322  
  1323  	// Things without pointers should be in sym.SNOPTRDATA or sym.SNOPTRBSS;
  1324  	// everything we see should have pointers and should therefore have a type.
  1325  	if typ == 0 {
  1326  		switch ldr.SymName(s) {
  1327  		case "runtime.data", "runtime.edata", "runtime.bss", "runtime.ebss":
  1328  			// Ignore special symbols that are sometimes laid out
  1329  			// as real symbols. See comment about dyld on darwin in
  1330  			// the address function.
  1331  			return
  1332  		}
  1333  		p.ctxt.Errorf(p.sym.Sym(), "missing Go type information for global symbol %s: size %d", ldr.SymName(s), ldr.SymSize(s))
  1334  		return
  1335  	}
  1336  
  1337  	ptrsize := int64(p.ctxt.Arch.PtrSize)
  1338  	typData := ldr.Data(typ)
  1339  	nptr := decodetypePtrdata(p.ctxt.Arch, typData) / ptrsize
  1340  
  1341  	if debugGCProg {
  1342  		fmt.Fprintf(os.Stderr, "gcprog sym: %s at %d (ptr=%d+%d)\n", ldr.SymName(s), ldr.SymValue(s), ldr.SymValue(s)/ptrsize, nptr)
  1343  	}
  1344  
  1345  	sval := ldr.SymValue(s)
  1346  	if decodetypeUsegcprog(p.ctxt.Arch, typData) == 0 {
  1347  		// Copy pointers from mask into program.
  1348  		mask := decodetypeGcmask(p.ctxt, typ)
  1349  		for i := int64(0); i < nptr; i++ {
  1350  			if (mask[i/8]>>uint(i%8))&1 != 0 {
  1351  				p.w.Ptr(sval/ptrsize + i)
  1352  			}
  1353  		}
  1354  		return
  1355  	}
  1356  
  1357  	// Copy program.
  1358  	prog := decodetypeGcprog(p.ctxt, typ)
  1359  	p.w.ZeroUntil(sval / ptrsize)
  1360  	p.w.Append(prog[4:], nptr)
  1361  }
  1362  
  1363  // cutoff is the maximum data section size permitted by the linker
  1364  // (see issue #9862).
  1365  const cutoff = 2e9 // 2 GB (or so; looks better in errors than 2^31)
  1366  
  1367  // check accumulated size of data sections
  1368  func (state *dodataState) checkdatsize(symn sym.SymKind) {
  1369  	if state.datsize > cutoff {
  1370  		Errorf(nil, "too much data, last section %v (%d, over %v bytes)", symn, state.datsize, cutoff)
  1371  	}
  1372  }
  1373  
  1374  func checkSectSize(sect *sym.Section) {
  1375  	// TODO: consider using 4 GB size limit for DWARF sections, and
  1376  	// make sure we generate unsigned offset in relocations and check
  1377  	// for overflow.
  1378  	if sect.Length > cutoff {
  1379  		Errorf(nil, "too much data in section %s (%d, over %v bytes)", sect.Name, sect.Length, cutoff)
  1380  	}
  1381  }
  1382  
  1383  // fixZeroSizedSymbols gives a few special symbols with zero size some space.
  1384  func fixZeroSizedSymbols(ctxt *Link) {
  1385  	// The values in moduledata are filled out by relocations
  1386  	// pointing to the addresses of these special symbols.
  1387  	// Typically these symbols have no size and are not laid
  1388  	// out with their matching section.
  1389  	//
  1390  	// However on darwin, dyld will find the special symbol
  1391  	// in the first loaded module, even though it is local.
  1392  	//
  1393  	// (An hypothesis, formed without looking in the dyld sources:
  1394  	// these special symbols have no size, so their address
  1395  	// matches a real symbol. The dynamic linker assumes we
  1396  	// want the normal symbol with the same address and finds
  1397  	// it in the other module.)
  1398  	//
  1399  	// To work around this we lay out the symbls whose
  1400  	// addresses are vital for multi-module programs to work
  1401  	// as normal symbols, and give them a little size.
  1402  	//
  1403  	// On AIX, as all DATA sections are merged together, ld might not put
  1404  	// these symbols at the beginning of their respective section if there
  1405  	// aren't real symbols, their alignment might not match the
  1406  	// first symbol alignment. Therefore, there are explicitly put at the
  1407  	// beginning of their section with the same alignment.
  1408  	if !(ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin) && !(ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal) {
  1409  		return
  1410  	}
  1411  
  1412  	ldr := ctxt.loader
  1413  	bss := ldr.CreateSymForUpdate("runtime.bss", 0)
  1414  	bss.SetSize(8)
  1415  	ldr.SetAttrSpecial(bss.Sym(), false)
  1416  
  1417  	ebss := ldr.CreateSymForUpdate("runtime.ebss", 0)
  1418  	ldr.SetAttrSpecial(ebss.Sym(), false)
  1419  
  1420  	data := ldr.CreateSymForUpdate("runtime.data", 0)
  1421  	data.SetSize(8)
  1422  	ldr.SetAttrSpecial(data.Sym(), false)
  1423  
  1424  	edata := ldr.CreateSymForUpdate("runtime.edata", 0)
  1425  	ldr.SetAttrSpecial(edata.Sym(), false)
  1426  
  1427  	if ctxt.HeadType == objabi.Haix {
  1428  		// XCOFFTOC symbols are part of .data section.
  1429  		edata.SetType(sym.SXCOFFTOC)
  1430  	}
  1431  
  1432  	noptrbss := ldr.CreateSymForUpdate("runtime.noptrbss", 0)
  1433  	noptrbss.SetSize(8)
  1434  	ldr.SetAttrSpecial(noptrbss.Sym(), false)
  1435  
  1436  	enoptrbss := ldr.CreateSymForUpdate("runtime.enoptrbss", 0)
  1437  	ldr.SetAttrSpecial(enoptrbss.Sym(), false)
  1438  
  1439  	noptrdata := ldr.CreateSymForUpdate("runtime.noptrdata", 0)
  1440  	noptrdata.SetSize(8)
  1441  	ldr.SetAttrSpecial(noptrdata.Sym(), false)
  1442  
  1443  	enoptrdata := ldr.CreateSymForUpdate("runtime.enoptrdata", 0)
  1444  	ldr.SetAttrSpecial(enoptrdata.Sym(), false)
  1445  
  1446  	types := ldr.CreateSymForUpdate("runtime.types", 0)
  1447  	types.SetType(sym.STYPE)
  1448  	types.SetSize(8)
  1449  	ldr.SetAttrSpecial(types.Sym(), false)
  1450  
  1451  	etypes := ldr.CreateSymForUpdate("runtime.etypes", 0)
  1452  	etypes.SetType(sym.SFUNCTAB)
  1453  	ldr.SetAttrSpecial(etypes.Sym(), false)
  1454  
  1455  	if ctxt.HeadType == objabi.Haix {
  1456  		rodata := ldr.CreateSymForUpdate("runtime.rodata", 0)
  1457  		rodata.SetType(sym.SSTRING)
  1458  		rodata.SetSize(8)
  1459  		ldr.SetAttrSpecial(rodata.Sym(), false)
  1460  
  1461  		erodata := ldr.CreateSymForUpdate("runtime.erodata", 0)
  1462  		ldr.SetAttrSpecial(erodata.Sym(), false)
  1463  	}
  1464  }
  1465  
  1466  // makeRelroForSharedLib creates a section of readonly data if necessary.
  1467  func (state *dodataState) makeRelroForSharedLib(target *Link) {
  1468  	if !target.UseRelro() {
  1469  		return
  1470  	}
  1471  
  1472  	// "read only" data with relocations needs to go in its own section
  1473  	// when building a shared library. We do this by boosting objects of
  1474  	// type SXXX with relocations to type SXXXRELRO.
  1475  	ldr := target.loader
  1476  	for _, symnro := range sym.ReadOnly {
  1477  		symnrelro := sym.RelROMap[symnro]
  1478  
  1479  		ro := []loader.Sym{}
  1480  		relro := state.data[symnrelro]
  1481  
  1482  		for _, s := range state.data[symnro] {
  1483  			relocs := ldr.Relocs(s)
  1484  			isRelro := relocs.Count() > 0
  1485  			switch state.symType(s) {
  1486  			case sym.STYPE, sym.STYPERELRO, sym.SGOFUNCRELRO:
  1487  				// Symbols are not sorted yet, so it is possible
  1488  				// that an Outer symbol has been changed to a
  1489  				// relro Type before it reaches here.
  1490  				isRelro = true
  1491  			case sym.SFUNCTAB:
  1492  				if ldr.SymName(s) == "runtime.etypes" {
  1493  					// runtime.etypes must be at the end of
  1494  					// the relro data.
  1495  					isRelro = true
  1496  				}
  1497  			case sym.SGOFUNC:
  1498  				// The only SGOFUNC symbols that contain relocations are .stkobj,
  1499  				// and their relocations are of type objabi.R_ADDROFF,
  1500  				// which always get resolved during linking.
  1501  				isRelro = false
  1502  			}
  1503  			if isRelro {
  1504  				state.setSymType(s, symnrelro)
  1505  				if outer := ldr.OuterSym(s); outer != 0 {
  1506  					state.setSymType(outer, symnrelro)
  1507  				}
  1508  				relro = append(relro, s)
  1509  			} else {
  1510  				ro = append(ro, s)
  1511  			}
  1512  		}
  1513  
  1514  		// Check that we haven't made two symbols with the same .Outer into
  1515  		// different types (because references two symbols with non-nil Outer
  1516  		// become references to the outer symbol + offset it's vital that the
  1517  		// symbol and the outer end up in the same section).
  1518  		for _, s := range relro {
  1519  			if outer := ldr.OuterSym(s); outer != 0 {
  1520  				st := state.symType(s)
  1521  				ost := state.symType(outer)
  1522  				if st != ost {
  1523  					state.ctxt.Errorf(s, "inconsistent types for symbol and its Outer %s (%v != %v)",
  1524  						ldr.SymName(outer), st, ost)
  1525  				}
  1526  			}
  1527  		}
  1528  
  1529  		state.data[symnro] = ro
  1530  		state.data[symnrelro] = relro
  1531  	}
  1532  }
  1533  
  1534  // dodataState holds bits of state information needed by dodata() and the
  1535  // various helpers it calls. The lifetime of these items should not extend
  1536  // past the end of dodata().
  1537  type dodataState struct {
  1538  	// Link context
  1539  	ctxt *Link
  1540  	// Data symbols bucketed by type.
  1541  	data [sym.SXREF][]loader.Sym
  1542  	// Max alignment for each flavor of data symbol.
  1543  	dataMaxAlign [sym.SXREF]int32
  1544  	// Overridden sym type
  1545  	symGroupType []sym.SymKind
  1546  	// Current data size so far.
  1547  	datsize int64
  1548  }
  1549  
  1550  // A note on symType/setSymType below:
  1551  //
  1552  // In the legacy linker, the types of symbols (notably data symbols) are
  1553  // changed during the symtab() phase so as to insure that similar symbols
  1554  // are bucketed together, then their types are changed back again during
  1555  // dodata. Symbol to section assignment also plays tricks along these lines
  1556  // in the case where a relro segment is needed.
  1557  //
  1558  // The value returned from setType() below reflects the effects of
  1559  // any overrides made by symtab and/or dodata.
  1560  
  1561  // symType returns the (possibly overridden) type of 's'.
  1562  func (state *dodataState) symType(s loader.Sym) sym.SymKind {
  1563  	if int(s) < len(state.symGroupType) {
  1564  		if override := state.symGroupType[s]; override != 0 {
  1565  			return override
  1566  		}
  1567  	}
  1568  	return state.ctxt.loader.SymType(s)
  1569  }
  1570  
  1571  // setSymType sets a new override type for 's'.
  1572  func (state *dodataState) setSymType(s loader.Sym, kind sym.SymKind) {
  1573  	if s == 0 {
  1574  		panic("bad")
  1575  	}
  1576  	if int(s) < len(state.symGroupType) {
  1577  		state.symGroupType[s] = kind
  1578  	} else {
  1579  		su := state.ctxt.loader.MakeSymbolUpdater(s)
  1580  		su.SetType(kind)
  1581  	}
  1582  }
  1583  
  1584  func (ctxt *Link) dodata(symGroupType []sym.SymKind) {
  1585  
  1586  	// Give zeros sized symbols space if necessary.
  1587  	fixZeroSizedSymbols(ctxt)
  1588  
  1589  	// Collect data symbols by type into data.
  1590  	state := dodataState{ctxt: ctxt, symGroupType: symGroupType}
  1591  	ldr := ctxt.loader
  1592  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
  1593  		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) || ldr.AttrSubSymbol(s) ||
  1594  			!ldr.TopLevelSym(s) {
  1595  			continue
  1596  		}
  1597  
  1598  		st := state.symType(s)
  1599  
  1600  		if st <= sym.STEXT || st >= sym.SXREF {
  1601  			continue
  1602  		}
  1603  		state.data[st] = append(state.data[st], s)
  1604  
  1605  		// Similarly with checking the onlist attr.
  1606  		if ldr.AttrOnList(s) {
  1607  			log.Fatalf("symbol %s listed multiple times", ldr.SymName(s))
  1608  		}
  1609  		ldr.SetAttrOnList(s, true)
  1610  	}
  1611  
  1612  	// Now that we have the data symbols, but before we start
  1613  	// to assign addresses, record all the necessary
  1614  	// dynamic relocations. These will grow the relocation
  1615  	// symbol, which is itself data.
  1616  	//
  1617  	// On darwin, we need the symbol table numbers for dynreloc.
  1618  	if ctxt.HeadType == objabi.Hdarwin {
  1619  		machosymorder(ctxt)
  1620  	}
  1621  	state.dynreloc(ctxt)
  1622  
  1623  	// Move any RO data with relocations to a separate section.
  1624  	state.makeRelroForSharedLib(ctxt)
  1625  
  1626  	// Set alignment for the symbol with the largest known index,
  1627  	// so as to trigger allocation of the loader's internal
  1628  	// alignment array. This will avoid data races in the parallel
  1629  	// section below.
  1630  	lastSym := loader.Sym(ldr.NSym() - 1)
  1631  	ldr.SetSymAlign(lastSym, ldr.SymAlign(lastSym))
  1632  
  1633  	// Sort symbols.
  1634  	var wg sync.WaitGroup
  1635  	for symn := range state.data {
  1636  		symn := sym.SymKind(symn)
  1637  		wg.Add(1)
  1638  		go func() {
  1639  			state.data[symn], state.dataMaxAlign[symn] = state.dodataSect(ctxt, symn, state.data[symn])
  1640  			wg.Done()
  1641  		}()
  1642  	}
  1643  	wg.Wait()
  1644  
  1645  	if ctxt.IsELF {
  1646  		// Make .rela and .rela.plt contiguous, the ELF ABI requires this
  1647  		// and Solaris actually cares.
  1648  		syms := state.data[sym.SELFROSECT]
  1649  		reli, plti := -1, -1
  1650  		for i, s := range syms {
  1651  			switch ldr.SymName(s) {
  1652  			case ".rel.plt", ".rela.plt":
  1653  				plti = i
  1654  			case ".rel", ".rela":
  1655  				reli = i
  1656  			}
  1657  		}
  1658  		if reli >= 0 && plti >= 0 && plti != reli+1 {
  1659  			var first, second int
  1660  			if plti > reli {
  1661  				first, second = reli, plti
  1662  			} else {
  1663  				first, second = plti, reli
  1664  			}
  1665  			rel, plt := syms[reli], syms[plti]
  1666  			copy(syms[first+2:], syms[first+1:second])
  1667  			syms[first+0] = rel
  1668  			syms[first+1] = plt
  1669  
  1670  			// Make sure alignment doesn't introduce a gap.
  1671  			// Setting the alignment explicitly prevents
  1672  			// symalign from basing it on the size and
  1673  			// getting it wrong.
  1674  			ldr.SetSymAlign(rel, int32(ctxt.Arch.RegSize))
  1675  			ldr.SetSymAlign(plt, int32(ctxt.Arch.RegSize))
  1676  		}
  1677  		state.data[sym.SELFROSECT] = syms
  1678  	}
  1679  
  1680  	if ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal {
  1681  		// These symbols must have the same alignment as their section.
  1682  		// Otherwise, ld might change the layout of Go sections.
  1683  		ldr.SetSymAlign(ldr.Lookup("runtime.data", 0), state.dataMaxAlign[sym.SDATA])
  1684  		ldr.SetSymAlign(ldr.Lookup("runtime.bss", 0), state.dataMaxAlign[sym.SBSS])
  1685  	}
  1686  
  1687  	// Create *sym.Section objects and assign symbols to sections for
  1688  	// data/rodata (and related) symbols.
  1689  	state.allocateDataSections(ctxt)
  1690  
  1691  	state.allocateSEHSections(ctxt)
  1692  
  1693  	// Create *sym.Section objects and assign symbols to sections for
  1694  	// DWARF symbols.
  1695  	state.allocateDwarfSections(ctxt)
  1696  
  1697  	/* number the sections */
  1698  	n := int16(1)
  1699  
  1700  	for _, sect := range Segtext.Sections {
  1701  		sect.Extnum = n
  1702  		n++
  1703  	}
  1704  	for _, sect := range Segrodata.Sections {
  1705  		sect.Extnum = n
  1706  		n++
  1707  	}
  1708  	for _, sect := range Segrelrodata.Sections {
  1709  		sect.Extnum = n
  1710  		n++
  1711  	}
  1712  	for _, sect := range Segdata.Sections {
  1713  		sect.Extnum = n
  1714  		n++
  1715  	}
  1716  	for _, sect := range Segdwarf.Sections {
  1717  		sect.Extnum = n
  1718  		n++
  1719  	}
  1720  	for _, sect := range Segpdata.Sections {
  1721  		sect.Extnum = n
  1722  		n++
  1723  	}
  1724  	for _, sect := range Segxdata.Sections {
  1725  		sect.Extnum = n
  1726  		n++
  1727  	}
  1728  }
  1729  
  1730  // allocateDataSectionForSym creates a new sym.Section into which a
  1731  // single symbol will be placed. Here "seg" is the segment into which
  1732  // the section will go, "s" is the symbol to be placed into the new
  1733  // section, and "rwx" contains permissions for the section.
  1734  func (state *dodataState) allocateDataSectionForSym(seg *sym.Segment, s loader.Sym, rwx int) *sym.Section {
  1735  	ldr := state.ctxt.loader
  1736  	sname := ldr.SymName(s)
  1737  	if strings.HasPrefix(sname, "go:") {
  1738  		sname = ".go." + sname[len("go:"):]
  1739  	}
  1740  	sect := addsection(ldr, state.ctxt.Arch, seg, sname, rwx)
  1741  	sect.Align = symalign(ldr, s)
  1742  	state.datsize = Rnd(state.datsize, int64(sect.Align))
  1743  	sect.Vaddr = uint64(state.datsize)
  1744  	return sect
  1745  }
  1746  
  1747  // allocateNamedDataSection creates a new sym.Section for a category
  1748  // of data symbols. Here "seg" is the segment into which the section
  1749  // will go, "sName" is the name to give to the section, "types" is a
  1750  // range of symbol types to be put into the section, and "rwx"
  1751  // contains permissions for the section.
  1752  func (state *dodataState) allocateNamedDataSection(seg *sym.Segment, sName string, types []sym.SymKind, rwx int) *sym.Section {
  1753  	sect := addsection(state.ctxt.loader, state.ctxt.Arch, seg, sName, rwx)
  1754  	if len(types) == 0 {
  1755  		sect.Align = 1
  1756  	} else if len(types) == 1 {
  1757  		sect.Align = state.dataMaxAlign[types[0]]
  1758  	} else {
  1759  		for _, symn := range types {
  1760  			align := state.dataMaxAlign[symn]
  1761  			if sect.Align < align {
  1762  				sect.Align = align
  1763  			}
  1764  		}
  1765  	}
  1766  	state.datsize = Rnd(state.datsize, int64(sect.Align))
  1767  	sect.Vaddr = uint64(state.datsize)
  1768  	return sect
  1769  }
  1770  
  1771  // assignDsymsToSection assigns a collection of data symbols to a
  1772  // newly created section. "sect" is the section into which to place
  1773  // the symbols, "syms" holds the list of symbols to assign,
  1774  // "forceType" (if non-zero) contains a new sym type to apply to each
  1775  // sym during the assignment, and "aligner" is a hook to call to
  1776  // handle alignment during the assignment process.
  1777  func (state *dodataState) assignDsymsToSection(sect *sym.Section, syms []loader.Sym, forceType sym.SymKind, aligner func(state *dodataState, datsize int64, s loader.Sym) int64) {
  1778  	ldr := state.ctxt.loader
  1779  	for _, s := range syms {
  1780  		state.datsize = aligner(state, state.datsize, s)
  1781  		ldr.SetSymSect(s, sect)
  1782  		if forceType != sym.Sxxx {
  1783  			state.setSymType(s, forceType)
  1784  		}
  1785  		ldr.SetSymValue(s, int64(uint64(state.datsize)-sect.Vaddr))
  1786  		state.datsize += ldr.SymSize(s)
  1787  	}
  1788  	sect.Length = uint64(state.datsize) - sect.Vaddr
  1789  }
  1790  
  1791  func (state *dodataState) assignToSection(sect *sym.Section, symn sym.SymKind, forceType sym.SymKind) {
  1792  	state.assignDsymsToSection(sect, state.data[symn], forceType, aligndatsize)
  1793  	state.checkdatsize(symn)
  1794  }
  1795  
  1796  // allocateSingleSymSections walks through the bucketed data symbols
  1797  // with type 'symn', creates a new section for each sym, and assigns
  1798  // the sym to a newly created section. Section name is set from the
  1799  // symbol name. "Seg" is the segment into which to place the new
  1800  // section, "forceType" is the new sym.SymKind to assign to the symbol
  1801  // within the section, and "rwx" holds section permissions.
  1802  func (state *dodataState) allocateSingleSymSections(seg *sym.Segment, symn sym.SymKind, forceType sym.SymKind, rwx int) {
  1803  	ldr := state.ctxt.loader
  1804  	for _, s := range state.data[symn] {
  1805  		sect := state.allocateDataSectionForSym(seg, s, rwx)
  1806  		ldr.SetSymSect(s, sect)
  1807  		state.setSymType(s, forceType)
  1808  		ldr.SetSymValue(s, int64(uint64(state.datsize)-sect.Vaddr))
  1809  		state.datsize += ldr.SymSize(s)
  1810  		sect.Length = uint64(state.datsize) - sect.Vaddr
  1811  	}
  1812  	state.checkdatsize(symn)
  1813  }
  1814  
  1815  // allocateNamedSectionAndAssignSyms creates a new section with the
  1816  // specified name, then walks through the bucketed data symbols with
  1817  // type 'symn' and assigns each of them to this new section. "Seg" is
  1818  // the segment into which to place the new section, "secName" is the
  1819  // name to give to the new section, "forceType" (if non-zero) contains
  1820  // a new sym type to apply to each sym during the assignment, and
  1821  // "rwx" holds section permissions.
  1822  func (state *dodataState) allocateNamedSectionAndAssignSyms(seg *sym.Segment, secName string, symn sym.SymKind, forceType sym.SymKind, rwx int) *sym.Section {
  1823  
  1824  	sect := state.allocateNamedDataSection(seg, secName, []sym.SymKind{symn}, rwx)
  1825  	state.assignDsymsToSection(sect, state.data[symn], forceType, aligndatsize)
  1826  	return sect
  1827  }
  1828  
  1829  // allocateDataSections allocates sym.Section objects for data/rodata
  1830  // (and related) symbols, and then assigns symbols to those sections.
  1831  func (state *dodataState) allocateDataSections(ctxt *Link) {
  1832  	// Allocate sections.
  1833  	// Data is processed before segtext, because we need
  1834  	// to see all symbols in the .data and .bss sections in order
  1835  	// to generate garbage collection information.
  1836  
  1837  	// Writable data sections that do not need any specialized handling.
  1838  	writable := []sym.SymKind{
  1839  		sym.SBUILDINFO,
  1840  		sym.SELFSECT,
  1841  		sym.SMACHO,
  1842  		sym.SMACHOGOT,
  1843  		sym.SWINDOWS,
  1844  	}
  1845  	for _, symn := range writable {
  1846  		state.allocateSingleSymSections(&Segdata, symn, sym.SDATA, 06)
  1847  	}
  1848  	ldr := ctxt.loader
  1849  
  1850  	// .got
  1851  	if len(state.data[sym.SELFGOT]) > 0 {
  1852  		state.allocateNamedSectionAndAssignSyms(&Segdata, ".got", sym.SELFGOT, sym.SDATA, 06)
  1853  	}
  1854  
  1855  	/* pointer-free data */
  1856  	sect := state.allocateNamedSectionAndAssignSyms(&Segdata, ".noptrdata", sym.SNOPTRDATA, sym.SDATA, 06)
  1857  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.noptrdata", 0), sect)
  1858  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.enoptrdata", 0), sect)
  1859  
  1860  	hasinitarr := ctxt.linkShared
  1861  
  1862  	/* shared library initializer */
  1863  	switch ctxt.BuildMode {
  1864  	case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePlugin:
  1865  		hasinitarr = true
  1866  	}
  1867  
  1868  	if ctxt.HeadType == objabi.Haix {
  1869  		if len(state.data[sym.SINITARR]) > 0 {
  1870  			Errorf(nil, "XCOFF format doesn't allow .init_array section")
  1871  		}
  1872  	}
  1873  
  1874  	if hasinitarr && len(state.data[sym.SINITARR]) > 0 {
  1875  		state.allocateNamedSectionAndAssignSyms(&Segdata, ".init_array", sym.SINITARR, sym.Sxxx, 06)
  1876  	}
  1877  
  1878  	/* data */
  1879  	sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".data", sym.SDATA, sym.SDATA, 06)
  1880  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.data", 0), sect)
  1881  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.edata", 0), sect)
  1882  	dataGcEnd := state.datsize - int64(sect.Vaddr)
  1883  
  1884  	// On AIX, TOC entries must be the last of .data
  1885  	// These aren't part of gc as they won't change during the runtime.
  1886  	state.assignToSection(sect, sym.SXCOFFTOC, sym.SDATA)
  1887  	state.checkdatsize(sym.SDATA)
  1888  	sect.Length = uint64(state.datsize) - sect.Vaddr
  1889  
  1890  	/* bss */
  1891  	sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".bss", sym.SBSS, sym.Sxxx, 06)
  1892  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.bss", 0), sect)
  1893  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.ebss", 0), sect)
  1894  	bssGcEnd := state.datsize - int64(sect.Vaddr)
  1895  
  1896  	// Emit gcdata for bss symbols now that symbol values have been assigned.
  1897  	gcsToEmit := []struct {
  1898  		symName string
  1899  		symKind sym.SymKind
  1900  		gcEnd   int64
  1901  	}{
  1902  		{"runtime.gcdata", sym.SDATA, dataGcEnd},
  1903  		{"runtime.gcbss", sym.SBSS, bssGcEnd},
  1904  	}
  1905  	for _, g := range gcsToEmit {
  1906  		var gc GCProg
  1907  		gc.Init(ctxt, g.symName)
  1908  		for _, s := range state.data[g.symKind] {
  1909  			gc.AddSym(s)
  1910  		}
  1911  		gc.End(g.gcEnd)
  1912  	}
  1913  
  1914  	/* pointer-free bss */
  1915  	sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".noptrbss", sym.SNOPTRBSS, sym.Sxxx, 06)
  1916  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.noptrbss", 0), sect)
  1917  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.enoptrbss", 0), sect)
  1918  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.end", 0), sect)
  1919  
  1920  	// Code coverage counters are assigned to the .noptrbss section.
  1921  	// We assign them in a separate pass so that they stay aggregated
  1922  	// together in a single blob (coverage runtime depends on this).
  1923  	covCounterDataStartOff = sect.Length
  1924  	state.assignToSection(sect, sym.SCOVERAGE_COUNTER, sym.SNOPTRBSS)
  1925  	covCounterDataLen = sect.Length - covCounterDataStartOff
  1926  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.covctrs", 0), sect)
  1927  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.ecovctrs", 0), sect)
  1928  
  1929  	// Coverage instrumentation counters for libfuzzer.
  1930  	if len(state.data[sym.SLIBFUZZER_8BIT_COUNTER]) > 0 {
  1931  		sect := state.allocateNamedSectionAndAssignSyms(&Segdata, ".go.fuzzcntrs", sym.SLIBFUZZER_8BIT_COUNTER, sym.Sxxx, 06)
  1932  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.__start___sancov_cntrs", 0), sect)
  1933  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.__stop___sancov_cntrs", 0), sect)
  1934  		ldr.SetSymSect(ldr.LookupOrCreateSym("internal/fuzz._counters", 0), sect)
  1935  		ldr.SetSymSect(ldr.LookupOrCreateSym("internal/fuzz._ecounters", 0), sect)
  1936  	}
  1937  
  1938  	if len(state.data[sym.STLSBSS]) > 0 {
  1939  		var sect *sym.Section
  1940  		// FIXME: not clear why it is sometimes necessary to suppress .tbss section creation.
  1941  		if (ctxt.IsELF || ctxt.HeadType == objabi.Haix) && (ctxt.LinkMode == LinkExternal || !*FlagD) {
  1942  			sect = addsection(ldr, ctxt.Arch, &Segdata, ".tbss", 06)
  1943  			sect.Align = int32(ctxt.Arch.PtrSize)
  1944  			// FIXME: why does this need to be set to zero?
  1945  			sect.Vaddr = 0
  1946  		}
  1947  		state.datsize = 0
  1948  
  1949  		for _, s := range state.data[sym.STLSBSS] {
  1950  			state.datsize = aligndatsize(state, state.datsize, s)
  1951  			if sect != nil {
  1952  				ldr.SetSymSect(s, sect)
  1953  			}
  1954  			ldr.SetSymValue(s, state.datsize)
  1955  			state.datsize += ldr.SymSize(s)
  1956  		}
  1957  		state.checkdatsize(sym.STLSBSS)
  1958  
  1959  		if sect != nil {
  1960  			sect.Length = uint64(state.datsize)
  1961  		}
  1962  	}
  1963  
  1964  	/*
  1965  	 * We finished data, begin read-only data.
  1966  	 * Not all systems support a separate read-only non-executable data section.
  1967  	 * ELF and Windows PE systems do.
  1968  	 * OS X and Plan 9 do not.
  1969  	 * And if we're using external linking mode, the point is moot,
  1970  	 * since it's not our decision; that code expects the sections in
  1971  	 * segtext.
  1972  	 */
  1973  	var segro *sym.Segment
  1974  	if ctxt.IsELF && ctxt.LinkMode == LinkInternal {
  1975  		segro = &Segrodata
  1976  	} else if ctxt.HeadType == objabi.Hwindows {
  1977  		segro = &Segrodata
  1978  	} else {
  1979  		segro = &Segtext
  1980  	}
  1981  
  1982  	state.datsize = 0
  1983  
  1984  	/* read-only executable ELF, Mach-O sections */
  1985  	if len(state.data[sym.STEXT]) != 0 {
  1986  		culprit := ldr.SymName(state.data[sym.STEXT][0])
  1987  		Errorf(nil, "dodata found an sym.STEXT symbol: %s", culprit)
  1988  	}
  1989  	state.allocateSingleSymSections(&Segtext, sym.SELFRXSECT, sym.SRODATA, 05)
  1990  	state.allocateSingleSymSections(&Segtext, sym.SMACHOPLT, sym.SRODATA, 05)
  1991  
  1992  	/* read-only data */
  1993  	sect = state.allocateNamedDataSection(segro, ".rodata", sym.ReadOnly, 04)
  1994  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.rodata", 0), sect)
  1995  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.erodata", 0), sect)
  1996  	if !ctxt.UseRelro() {
  1997  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.types", 0), sect)
  1998  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.etypes", 0), sect)
  1999  	}
  2000  	for _, symn := range sym.ReadOnly {
  2001  		symnStartValue := state.datsize
  2002  		if len(state.data[symn]) != 0 {
  2003  			symnStartValue = aligndatsize(state, symnStartValue, state.data[symn][0])
  2004  		}
  2005  		state.assignToSection(sect, symn, sym.SRODATA)
  2006  		setCarrierSize(symn, state.datsize-symnStartValue)
  2007  		if ctxt.HeadType == objabi.Haix {
  2008  			// Read-only symbols might be wrapped inside their outer
  2009  			// symbol.
  2010  			// XCOFF symbol table needs to know the size of
  2011  			// these outer symbols.
  2012  			xcoffUpdateOuterSize(ctxt, state.datsize-symnStartValue, symn)
  2013  		}
  2014  	}
  2015  
  2016  	/* read-only ELF, Mach-O sections */
  2017  	state.allocateSingleSymSections(segro, sym.SELFROSECT, sym.SRODATA, 04)
  2018  
  2019  	// There is some data that are conceptually read-only but are written to by
  2020  	// relocations. On GNU systems, we can arrange for the dynamic linker to
  2021  	// mprotect sections after relocations are applied by giving them write
  2022  	// permissions in the object file and calling them ".data.rel.ro.FOO". We
  2023  	// divide the .rodata section between actual .rodata and .data.rel.ro.rodata,
  2024  	// but for the other sections that this applies to, we just write a read-only
  2025  	// .FOO section or a read-write .data.rel.ro.FOO section depending on the
  2026  	// situation.
  2027  	// TODO(mwhudson): It would make sense to do this more widely, but it makes
  2028  	// the system linker segfault on darwin.
  2029  	const relroPerm = 06
  2030  	const fallbackPerm = 04
  2031  	relroSecPerm := fallbackPerm
  2032  	genrelrosecname := func(suffix string) string {
  2033  		if suffix == "" {
  2034  			return ".rodata"
  2035  		}
  2036  		return suffix
  2037  	}
  2038  	seg := segro
  2039  
  2040  	if ctxt.UseRelro() {
  2041  		segrelro := &Segrelrodata
  2042  		if ctxt.LinkMode == LinkExternal && !ctxt.IsAIX() && !ctxt.IsDarwin() {
  2043  			// Using a separate segment with an external
  2044  			// linker results in some programs moving
  2045  			// their data sections unexpectedly, which
  2046  			// corrupts the moduledata. So we use the
  2047  			// rodata segment and let the external linker
  2048  			// sort out a rel.ro segment.
  2049  			segrelro = segro
  2050  		} else {
  2051  			// Reset datsize for new segment.
  2052  			state.datsize = 0
  2053  		}
  2054  
  2055  		if !ctxt.IsDarwin() { // We don't need the special names on darwin.
  2056  			genrelrosecname = func(suffix string) string {
  2057  				return ".data.rel.ro" + suffix
  2058  			}
  2059  		}
  2060  
  2061  		relroReadOnly := []sym.SymKind{}
  2062  		for _, symnro := range sym.ReadOnly {
  2063  			symn := sym.RelROMap[symnro]
  2064  			relroReadOnly = append(relroReadOnly, symn)
  2065  		}
  2066  		seg = segrelro
  2067  		relroSecPerm = relroPerm
  2068  
  2069  		/* data only written by relocations */
  2070  		sect = state.allocateNamedDataSection(segrelro, genrelrosecname(""), relroReadOnly, relroSecPerm)
  2071  
  2072  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.types", 0), sect)
  2073  		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.etypes", 0), sect)
  2074  
  2075  		for i, symnro := range sym.ReadOnly {
  2076  			if i == 0 && symnro == sym.STYPE && ctxt.HeadType != objabi.Haix {
  2077  				// Skip forward so that no type
  2078  				// reference uses a zero offset.
  2079  				// This is unlikely but possible in small
  2080  				// programs with no other read-only data.
  2081  				state.datsize++
  2082  			}
  2083  
  2084  			symn := sym.RelROMap[symnro]
  2085  			symnStartValue := state.datsize
  2086  			if len(state.data[symn]) != 0 {
  2087  				symnStartValue = aligndatsize(state, symnStartValue, state.data[symn][0])
  2088  			}
  2089  
  2090  			for _, s := range state.data[symn] {
  2091  				outer := ldr.OuterSym(s)
  2092  				if s != 0 && ldr.SymSect(outer) != nil && ldr.SymSect(outer) != sect {
  2093  					ctxt.Errorf(s, "s.Outer (%s) in different section from s, %s != %s", ldr.SymName(outer), ldr.SymSect(outer).Name, sect.Name)
  2094  				}
  2095  			}
  2096  			state.assignToSection(sect, symn, sym.SRODATA)
  2097  			setCarrierSize(symn, state.datsize-symnStartValue)
  2098  			if ctxt.HeadType == objabi.Haix {
  2099  				// Read-only symbols might be wrapped inside their outer
  2100  				// symbol.
  2101  				// XCOFF symbol table needs to know the size of
  2102  				// these outer symbols.
  2103  				xcoffUpdateOuterSize(ctxt, state.datsize-symnStartValue, symn)
  2104  			}
  2105  		}
  2106  
  2107  		sect.Length = uint64(state.datsize) - sect.Vaddr
  2108  	}
  2109  
  2110  	/* typelink */
  2111  	sect = state.allocateNamedDataSection(seg, genrelrosecname(".typelink"), []sym.SymKind{sym.STYPELINK}, relroSecPerm)
  2112  
  2113  	typelink := ldr.CreateSymForUpdate("runtime.typelink", 0)
  2114  	ldr.SetSymSect(typelink.Sym(), sect)
  2115  	typelink.SetType(sym.SRODATA)
  2116  	state.datsize += typelink.Size()
  2117  	state.checkdatsize(sym.STYPELINK)
  2118  	sect.Length = uint64(state.datsize) - sect.Vaddr
  2119  
  2120  	/* itablink */
  2121  	sect = state.allocateNamedDataSection(seg, genrelrosecname(".itablink"), []sym.SymKind{sym.SITABLINK}, relroSecPerm)
  2122  
  2123  	itablink := ldr.CreateSymForUpdate("runtime.itablink", 0)
  2124  	ldr.SetSymSect(itablink.Sym(), sect)
  2125  	itablink.SetType(sym.SRODATA)
  2126  	state.datsize += itablink.Size()
  2127  	state.checkdatsize(sym.SITABLINK)
  2128  	sect.Length = uint64(state.datsize) - sect.Vaddr
  2129  
  2130  	/* gosymtab */
  2131  	sect = state.allocateNamedSectionAndAssignSyms(seg, genrelrosecname(".gosymtab"), sym.SSYMTAB, sym.SRODATA, relroSecPerm)
  2132  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.symtab", 0), sect)
  2133  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.esymtab", 0), sect)
  2134  
  2135  	/* gopclntab */
  2136  	sect = state.allocateNamedSectionAndAssignSyms(seg, genrelrosecname(".gopclntab"), sym.SPCLNTAB, sym.SRODATA, relroSecPerm)
  2137  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.pclntab", 0), sect)
  2138  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.pcheader", 0), sect)
  2139  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.funcnametab", 0), sect)
  2140  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.cutab", 0), sect)
  2141  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.filetab", 0), sect)
  2142  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.pctab", 0), sect)
  2143  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.functab", 0), sect)
  2144  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.epclntab", 0), sect)
  2145  	setCarrierSize(sym.SPCLNTAB, int64(sect.Length))
  2146  	if ctxt.HeadType == objabi.Haix {
  2147  		xcoffUpdateOuterSize(ctxt, int64(sect.Length), sym.SPCLNTAB)
  2148  	}
  2149  
  2150  	// 6g uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
  2151  	if state.datsize != int64(uint32(state.datsize)) {
  2152  		Errorf(nil, "read-only data segment too large: %d", state.datsize)
  2153  	}
  2154  
  2155  	siz := 0
  2156  	for symn := sym.SELFRXSECT; symn < sym.SXREF; symn++ {
  2157  		siz += len(state.data[symn])
  2158  	}
  2159  	ctxt.datap = make([]loader.Sym, 0, siz)
  2160  	for symn := sym.SELFRXSECT; symn < sym.SXREF; symn++ {
  2161  		ctxt.datap = append(ctxt.datap, state.data[symn]...)
  2162  	}
  2163  }
  2164  
  2165  // allocateDwarfSections allocates sym.Section objects for DWARF
  2166  // symbols, and assigns symbols to sections.
  2167  func (state *dodataState) allocateDwarfSections(ctxt *Link) {
  2168  
  2169  	alignOne := func(state *dodataState, datsize int64, s loader.Sym) int64 { return datsize }
  2170  
  2171  	ldr := ctxt.loader
  2172  	for i := 0; i < len(dwarfp); i++ {
  2173  		// First the section symbol.
  2174  		s := dwarfp[i].secSym()
  2175  		sect := state.allocateNamedDataSection(&Segdwarf, ldr.SymName(s), []sym.SymKind{}, 04)
  2176  		ldr.SetSymSect(s, sect)
  2177  		sect.Sym = sym.LoaderSym(s)
  2178  		curType := ldr.SymType(s)
  2179  		state.setSymType(s, sym.SRODATA)
  2180  		ldr.SetSymValue(s, int64(uint64(state.datsize)-sect.Vaddr))
  2181  		state.datsize += ldr.SymSize(s)
  2182  
  2183  		// Then any sub-symbols for the section symbol.
  2184  		subSyms := dwarfp[i].subSyms()
  2185  		state.assignDsymsToSection(sect, subSyms, sym.SRODATA, alignOne)
  2186  
  2187  		for j := 0; j < len(subSyms); j++ {
  2188  			s := subSyms[j]
  2189  			if ctxt.HeadType == objabi.Haix && curType == sym.SDWARFLOC {
  2190  				// Update the size of .debug_loc for this symbol's
  2191  				// package.
  2192  				addDwsectCUSize(".debug_loc", ldr.SymPkg(s), uint64(ldr.SymSize(s)))
  2193  			}
  2194  		}
  2195  		sect.Length = uint64(state.datsize) - sect.Vaddr
  2196  		checkSectSize(sect)
  2197  	}
  2198  }
  2199  
  2200  // allocateSEHSections allocate a sym.Section object for SEH
  2201  // symbols, and assigns symbols to sections.
  2202  func (state *dodataState) allocateSEHSections(ctxt *Link) {
  2203  	if len(sehp.pdata) > 0 {
  2204  		sect := state.allocateNamedDataSection(&Segpdata, ".pdata", []sym.SymKind{}, 04)
  2205  		state.assignDsymsToSection(sect, sehp.pdata, sym.SRODATA, aligndatsize)
  2206  		state.checkdatsize(sym.SSEHSECT)
  2207  	}
  2208  	if len(sehp.xdata) > 0 {
  2209  		sect := state.allocateNamedDataSection(&Segxdata, ".xdata", []sym.SymKind{}, 04)
  2210  		state.assignDsymsToSection(sect, sehp.xdata, sym.SRODATA, aligndatsize)
  2211  		state.checkdatsize(sym.SSEHSECT)
  2212  	}
  2213  }
  2214  
  2215  type symNameSize struct {
  2216  	name string
  2217  	sz   int64
  2218  	val  int64
  2219  	sym  loader.Sym
  2220  }
  2221  
  2222  func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader.Sym) (result []loader.Sym, maxAlign int32) {
  2223  	var head, tail, zerobase loader.Sym
  2224  	ldr := ctxt.loader
  2225  	sl := make([]symNameSize, len(syms))
  2226  
  2227  	// For ppc64, we want to interleave the .got and .toc sections
  2228  	// from input files. Both are type sym.SELFGOT, so in that case
  2229  	// we skip size comparison and do the name comparison instead
  2230  	// (conveniently, .got sorts before .toc).
  2231  	checkSize := symn != sym.SELFGOT
  2232  
  2233  	for k, s := range syms {
  2234  		ss := ldr.SymSize(s)
  2235  		sl[k] = symNameSize{sz: ss, sym: s}
  2236  		if !checkSize {
  2237  			sl[k].name = ldr.SymName(s)
  2238  		}
  2239  		ds := int64(len(ldr.Data(s)))
  2240  		switch {
  2241  		case ss < ds:
  2242  			ctxt.Errorf(s, "initialize bounds (%d < %d)", ss, ds)
  2243  		case ss < 0:
  2244  			ctxt.Errorf(s, "negative size (%d bytes)", ss)
  2245  		case ss > cutoff:
  2246  			ctxt.Errorf(s, "symbol too large (%d bytes)", ss)
  2247  		}
  2248  
  2249  		// If the usually-special section-marker symbols are being laid
  2250  		// out as regular symbols, put them either at the beginning or
  2251  		// end of their section.
  2252  		if (ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin) || (ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal) {
  2253  			switch ldr.SymName(s) {
  2254  			case "runtime.text", "runtime.bss", "runtime.data", "runtime.types", "runtime.rodata",
  2255  				"runtime.noptrdata", "runtime.noptrbss":
  2256  				head = s
  2257  				continue
  2258  			case "runtime.etext", "runtime.ebss", "runtime.edata", "runtime.etypes", "runtime.erodata",
  2259  				"runtime.enoptrdata", "runtime.enoptrbss":
  2260  				tail = s
  2261  				continue
  2262  			}
  2263  		}
  2264  	}
  2265  	zerobase = ldr.Lookup("runtime.zerobase", 0)
  2266  
  2267  	// Perform the sort.
  2268  	if symn != sym.SPCLNTAB {
  2269  		sort.Slice(sl, func(i, j int) bool {
  2270  			si, sj := sl[i].sym, sl[j].sym
  2271  			isz, jsz := sl[i].sz, sl[j].sz
  2272  			switch {
  2273  			case si == head, sj == tail:
  2274  				return true
  2275  			case sj == head, si == tail:
  2276  				return false
  2277  			// put zerobase right after all the zero-sized symbols,
  2278  			// so zero-sized symbols have the same address as zerobase.
  2279  			case si == zerobase:
  2280  				return jsz != 0 // zerobase < nonzero-sized
  2281  			case sj == zerobase:
  2282  				return isz == 0 // 0-sized < zerobase
  2283  			}
  2284  			if checkSize {
  2285  				if isz != jsz {
  2286  					return isz < jsz
  2287  				}
  2288  			} else {
  2289  				iname := sl[i].name
  2290  				jname := sl[j].name
  2291  				if iname != jname {
  2292  					return iname < jname
  2293  				}
  2294  			}
  2295  			return si < sj
  2296  		})
  2297  	} else {
  2298  		// PCLNTAB was built internally, and already has the proper order.
  2299  	}
  2300  
  2301  	// Set alignment, construct result
  2302  	syms = syms[:0]
  2303  	for k := range sl {
  2304  		s := sl[k].sym
  2305  		if s != head && s != tail {
  2306  			align := symalign(ldr, s)
  2307  			if maxAlign < align {
  2308  				maxAlign = align
  2309  			}
  2310  		}
  2311  		syms = append(syms, s)
  2312  	}
  2313  
  2314  	return syms, maxAlign
  2315  }
  2316  
  2317  // Add buildid to beginning of text segment, on non-ELF systems.
  2318  // Non-ELF binary formats are not always flexible enough to
  2319  // give us a place to put the Go build ID. On those systems, we put it
  2320  // at the very beginning of the text segment.
  2321  // This “header” is read by cmd/go.
  2322  func (ctxt *Link) textbuildid() {
  2323  	if ctxt.IsELF || *flagBuildid == "" {
  2324  		return
  2325  	}
  2326  
  2327  	ldr := ctxt.loader
  2328  	s := ldr.CreateSymForUpdate("go:buildid", 0)
  2329  	// The \xff is invalid UTF-8, meant to make it less likely
  2330  	// to find one of these accidentally.
  2331  	data := "\xff Go build ID: " + strconv.Quote(*flagBuildid) + "\n \xff"
  2332  	s.SetType(sym.STEXT)
  2333  	s.SetData([]byte(data))
  2334  	s.SetSize(int64(len(data)))
  2335  
  2336  	ctxt.Textp = append(ctxt.Textp, 0)
  2337  	copy(ctxt.Textp[1:], ctxt.Textp)
  2338  	ctxt.Textp[0] = s.Sym()
  2339  }
  2340  
  2341  func (ctxt *Link) buildinfo() {
  2342  	// Write the buildinfo symbol, which go version looks for.
  2343  	// The code reading this data is in package debug/buildinfo.
  2344  	ldr := ctxt.loader
  2345  	s := ldr.CreateSymForUpdate("go:buildinfo", 0)
  2346  	s.SetType(sym.SBUILDINFO)
  2347  	s.SetAlign(16)
  2348  	// The \xff is invalid UTF-8, meant to make it less likely
  2349  	// to find one of these accidentally.
  2350  	const prefix = "\xff Go buildinf:" // 14 bytes, plus 2 data bytes filled in below
  2351  	data := make([]byte, 32)
  2352  	copy(data, prefix)
  2353  	data[len(prefix)] = byte(ctxt.Arch.PtrSize)
  2354  	data[len(prefix)+1] = 0
  2355  	if ctxt.Arch.ByteOrder == binary.BigEndian {
  2356  		data[len(prefix)+1] = 1
  2357  	}
  2358  	data[len(prefix)+1] |= 2 // signals new pointer-free format
  2359  	data = appendString(data, strdata["runtime.buildVersion"])
  2360  	data = appendString(data, strdata["runtime.modinfo"])
  2361  	// MacOS linker gets very upset if the size os not a multiple of alignment.
  2362  	for len(data)%16 != 0 {
  2363  		data = append(data, 0)
  2364  	}
  2365  	s.SetData(data)
  2366  	s.SetSize(int64(len(data)))
  2367  
  2368  	// Add reference to go:buildinfo from the rodata section,
  2369  	// so that external linking with -Wl,--gc-sections does not
  2370  	// delete the build info.
  2371  	sr := ldr.CreateSymForUpdate("go:buildinfo.ref", 0)
  2372  	sr.SetType(sym.SRODATA)
  2373  	sr.SetAlign(int32(ctxt.Arch.PtrSize))
  2374  	sr.AddAddr(ctxt.Arch, s.Sym())
  2375  }
  2376  
  2377  // appendString appends s to data, prefixed by its varint-encoded length.
  2378  func appendString(data []byte, s string) []byte {
  2379  	var v [binary.MaxVarintLen64]byte
  2380  	n := binary.PutUvarint(v[:], uint64(len(s)))
  2381  	data = append(data, v[:n]...)
  2382  	data = append(data, s...)
  2383  	return data
  2384  }
  2385  
  2386  // assign addresses to text
  2387  func (ctxt *Link) textaddress() {
  2388  	addsection(ctxt.loader, ctxt.Arch, &Segtext, ".text", 05)
  2389  
  2390  	// Assign PCs in text segment.
  2391  	// Could parallelize, by assigning to text
  2392  	// and then letting threads copy down, but probably not worth it.
  2393  	sect := Segtext.Sections[0]
  2394  
  2395  	sect.Align = int32(Funcalign)
  2396  
  2397  	ldr := ctxt.loader
  2398  
  2399  	text := ctxt.xdefine("runtime.text", sym.STEXT, 0)
  2400  	etext := ctxt.xdefine("runtime.etext", sym.STEXT, 0)
  2401  	ldr.SetSymSect(text, sect)
  2402  	if ctxt.IsAIX() && ctxt.IsExternal() {
  2403  		// Setting runtime.text has a real symbol prevents ld to
  2404  		// change its base address resulting in wrong offsets for
  2405  		// reflect methods.
  2406  		u := ldr.MakeSymbolUpdater(text)
  2407  		u.SetAlign(sect.Align)
  2408  		u.SetSize(8)
  2409  	}
  2410  
  2411  	if (ctxt.DynlinkingGo() && ctxt.IsDarwin()) || (ctxt.IsAIX() && ctxt.IsExternal()) {
  2412  		ldr.SetSymSect(etext, sect)
  2413  		ctxt.Textp = append(ctxt.Textp, etext, 0)
  2414  		copy(ctxt.Textp[1:], ctxt.Textp)
  2415  		ctxt.Textp[0] = text
  2416  	}
  2417  
  2418  	start := uint64(Rnd(*FlagTextAddr, int64(Funcalign)))
  2419  	va := start
  2420  	n := 1
  2421  	sect.Vaddr = va
  2422  
  2423  	limit := thearch.TrampLimit
  2424  	if limit == 0 {
  2425  		limit = 1 << 63 // unlimited
  2426  	}
  2427  	if *FlagDebugTextSize != 0 {
  2428  		limit = uint64(*FlagDebugTextSize)
  2429  	}
  2430  	if *FlagDebugTramp > 1 {
  2431  		limit = 1 // debug mode, force generating trampolines for everything
  2432  	}
  2433  
  2434  	if ctxt.IsAIX() && ctxt.IsExternal() {
  2435  		// On AIX, normally we won't generate direct calls to external symbols,
  2436  		// except in one test, cmd/go/testdata/script/link_syso_issue33139.txt.
  2437  		// That test doesn't make much sense, and I'm not sure it ever works.
  2438  		// Just generate trampoline for now (which will turn a direct call to
  2439  		// an indirect call, which at least builds).
  2440  		limit = 1
  2441  	}
  2442  
  2443  	// First pass: assign addresses assuming the program is small and will
  2444  	// not require trampoline generation.
  2445  	big := false
  2446  	for _, s := range ctxt.Textp {
  2447  		sect, n, va = assignAddress(ctxt, sect, n, s, va, false, big)
  2448  		if va-start >= limit {
  2449  			big = true
  2450  			break
  2451  		}
  2452  	}
  2453  
  2454  	// Second pass: only if it is too big, insert trampolines for too-far
  2455  	// jumps and targets with unknown addresses.
  2456  	if big {
  2457  		// reset addresses
  2458  		for _, s := range ctxt.Textp {
  2459  			if s != text {
  2460  				resetAddress(ctxt, s)
  2461  			}
  2462  		}
  2463  		va = start
  2464  
  2465  		ntramps := 0
  2466  		var curPkg string
  2467  		for i, s := range ctxt.Textp {
  2468  			// When we find the first symbol in a package, perform a
  2469  			// single iteration that assigns temporary addresses to all
  2470  			// of the text in the same package, using the maximum possible
  2471  			// number of trampolines. This allows for better decisions to
  2472  			// be made regarding reachability and the need for trampolines.
  2473  			if symPkg := ldr.SymPkg(s); symPkg != "" && curPkg != symPkg {
  2474  				curPkg = symPkg
  2475  				vaTmp := va
  2476  				for j := i; j < len(ctxt.Textp); j++ {
  2477  					curSym := ctxt.Textp[j]
  2478  					if symPkg := ldr.SymPkg(curSym); symPkg == "" || curPkg != symPkg {
  2479  						break
  2480  					}
  2481  					// We do not pass big to assignAddress here, as this
  2482  					// can result in side effects such as section splitting.
  2483  					sect, n, vaTmp = assignAddress(ctxt, sect, n, curSym, vaTmp, false, false)
  2484  					vaTmp += maxSizeTrampolines(ctxt, ldr, curSym, false)
  2485  				}
  2486  			}
  2487  
  2488  			// Reset address for current symbol.
  2489  			if s != text {
  2490  				resetAddress(ctxt, s)
  2491  			}
  2492  
  2493  			// Assign actual address for current symbol.
  2494  			sect, n, va = assignAddress(ctxt, sect, n, s, va, false, big)
  2495  
  2496  			// Resolve jumps, adding trampolines if they are needed.
  2497  			trampoline(ctxt, s)
  2498  
  2499  			// lay down trampolines after each function
  2500  			for ; ntramps < len(ctxt.tramps); ntramps++ {
  2501  				tramp := ctxt.tramps[ntramps]
  2502  				if ctxt.IsAIX() && strings.HasPrefix(ldr.SymName(tramp), "runtime.text.") {
  2503  					// Already set in assignAddress
  2504  					continue
  2505  				}
  2506  				sect, n, va = assignAddress(ctxt, sect, n, tramp, va, true, big)
  2507  			}
  2508  		}
  2509  
  2510  		// merge tramps into Textp, keeping Textp in address order
  2511  		if ntramps != 0 {
  2512  			newtextp := make([]loader.Sym, 0, len(ctxt.Textp)+ntramps)
  2513  			i := 0
  2514  			for _, s := range ctxt.Textp {
  2515  				for ; i < ntramps && ldr.SymValue(ctxt.tramps[i]) < ldr.SymValue(s); i++ {
  2516  					newtextp = append(newtextp, ctxt.tramps[i])
  2517  				}
  2518  				newtextp = append(newtextp, s)
  2519  			}
  2520  			newtextp = append(newtextp, ctxt.tramps[i:ntramps]...)
  2521  
  2522  			ctxt.Textp = newtextp
  2523  		}
  2524  	}
  2525  
  2526  	// Add MinLC size after etext, so it won't collide with the next symbol
  2527  	// (which may confuse some symbolizer).
  2528  	sect.Length = va - sect.Vaddr + uint64(ctxt.Arch.MinLC)
  2529  	ldr.SetSymSect(etext, sect)
  2530  	if ldr.SymValue(etext) == 0 {
  2531  		// Set the address of the start/end symbols, if not already
  2532  		// (i.e. not darwin+dynlink or AIX+external, see above).
  2533  		ldr.SetSymValue(etext, int64(va))
  2534  		ldr.SetSymValue(text, int64(Segtext.Sections[0].Vaddr))
  2535  	}
  2536  }
  2537  
  2538  // assigns address for a text symbol, returns (possibly new) section, its number, and the address.
  2539  func assignAddress(ctxt *Link, sect *sym.Section, n int, s loader.Sym, va uint64, isTramp, big bool) (*sym.Section, int, uint64) {
  2540  	ldr := ctxt.loader
  2541  	if thearch.AssignAddress != nil {
  2542  		return thearch.AssignAddress(ldr, sect, n, s, va, isTramp)
  2543  	}
  2544  
  2545  	ldr.SetSymSect(s, sect)
  2546  	if ldr.AttrSubSymbol(s) {
  2547  		return sect, n, va
  2548  	}
  2549  
  2550  	align := ldr.SymAlign(s)
  2551  	if align == 0 {
  2552  		align = int32(Funcalign)
  2553  	}
  2554  	va = uint64(Rnd(int64(va), int64(align)))
  2555  	if sect.Align < align {
  2556  		sect.Align = align
  2557  	}
  2558  
  2559  	funcsize := uint64(MINFUNC) // spacing required for findfunctab
  2560  	if ldr.SymSize(s) > MINFUNC {
  2561  		funcsize = uint64(ldr.SymSize(s))
  2562  	}
  2563  
  2564  	// If we need to split text sections, and this function doesn't fit in the current
  2565  	// section, then create a new one.
  2566  	//
  2567  	// Only break at outermost syms.
  2568  	if big && splitTextSections(ctxt) && ldr.OuterSym(s) == 0 {
  2569  		// For debugging purposes, allow text size limit to be cranked down,
  2570  		// so as to stress test the code that handles multiple text sections.
  2571  		var textSizelimit uint64 = thearch.TrampLimit
  2572  		if *FlagDebugTextSize != 0 {
  2573  			textSizelimit = uint64(*FlagDebugTextSize)
  2574  		}
  2575  
  2576  		// Sanity check: make sure the limit is larger than any
  2577  		// individual text symbol.
  2578  		if funcsize > textSizelimit {
  2579  			panic(fmt.Sprintf("error: text size limit %d less than text symbol %s size of %d", textSizelimit, ldr.SymName(s), funcsize))
  2580  		}
  2581  
  2582  		if va-sect.Vaddr+funcsize+maxSizeTrampolines(ctxt, ldr, s, isTramp) > textSizelimit {
  2583  			sectAlign := int32(thearch.Funcalign)
  2584  			if ctxt.IsPPC64() {
  2585  				// Align the next text section to the worst case function alignment likely
  2586  				// to be encountered when processing function symbols. The start address
  2587  				// is rounded against the final alignment of the text section later on in
  2588  				// (*Link).address. This may happen due to usage of PCALIGN directives
  2589  				// larger than Funcalign, or usage of ISA 3.1 prefixed instructions
  2590  				// (see ISA 3.1 Book I 1.9).
  2591  				const ppc64maxFuncalign = 64
  2592  				sectAlign = ppc64maxFuncalign
  2593  				va = uint64(Rnd(int64(va), ppc64maxFuncalign))
  2594  			}
  2595  
  2596  			// Set the length for the previous text section
  2597  			sect.Length = va - sect.Vaddr
  2598  
  2599  			// Create new section, set the starting Vaddr
  2600  			sect = addsection(ctxt.loader, ctxt.Arch, &Segtext, ".text", 05)
  2601  
  2602  			sect.Vaddr = va
  2603  			sect.Align = sectAlign
  2604  			ldr.SetSymSect(s, sect)
  2605  
  2606  			// Create a symbol for the start of the secondary text sections
  2607  			ntext := ldr.CreateSymForUpdate(fmt.Sprintf("runtime.text.%d", n), 0)
  2608  			ntext.SetSect(sect)
  2609  			if ctxt.IsAIX() {
  2610  				// runtime.text.X must be a real symbol on AIX.
  2611  				// Assign its address directly in order to be the
  2612  				// first symbol of this new section.
  2613  				ntext.SetType(sym.STEXT)
  2614  				ntext.SetSize(int64(MINFUNC))
  2615  				ntext.SetOnList(true)
  2616  				ntext.SetAlign(sectAlign)
  2617  				ctxt.tramps = append(ctxt.tramps, ntext.Sym())
  2618  
  2619  				ntext.SetValue(int64(va))
  2620  				va += uint64(ntext.Size())
  2621  
  2622  				if align := ldr.SymAlign(s); align != 0 {
  2623  					va = uint64(Rnd(int64(va), int64(align)))
  2624  				} else {
  2625  					va = uint64(Rnd(int64(va), int64(Funcalign)))
  2626  				}
  2627  			}
  2628  			n++
  2629  		}
  2630  	}
  2631  
  2632  	ldr.SetSymValue(s, 0)
  2633  	for sub := s; sub != 0; sub = ldr.SubSym(sub) {
  2634  		ldr.SetSymValue(sub, ldr.SymValue(sub)+int64(va))
  2635  		if ctxt.Debugvlog > 2 {
  2636  			fmt.Println("assign text address:", ldr.SymName(sub), ldr.SymValue(sub))
  2637  		}
  2638  	}
  2639  
  2640  	va += funcsize
  2641  
  2642  	return sect, n, va
  2643  }
  2644  
  2645  func resetAddress(ctxt *Link, s loader.Sym) {
  2646  	ldr := ctxt.loader
  2647  	if ldr.OuterSym(s) != 0 {
  2648  		return
  2649  	}
  2650  	oldv := ldr.SymValue(s)
  2651  	for sub := s; sub != 0; sub = ldr.SubSym(sub) {
  2652  		ldr.SetSymValue(sub, ldr.SymValue(sub)-oldv)
  2653  	}
  2654  }
  2655  
  2656  // Return whether we may need to split text sections.
  2657  //
  2658  // On PPC64x, when external linking, a text section should not be
  2659  // larger than 2^25 bytes due to the size of call target offset field
  2660  // in the 'bl' instruction. Splitting into smaller text sections
  2661  // smaller than this limit allows the system linker to modify the long
  2662  // calls appropriately. The limit allows for the space needed for
  2663  // tables inserted by the linker.
  2664  //
  2665  // The same applies to Darwin/ARM64, with 2^27 byte threshold.
  2666  //
  2667  // Similarly for ARM, we split sections (at 2^25 bytes) to avoid
  2668  // inconsistencies between the Go linker's reachability calculations
  2669  // (e.g. will direct call from X to Y need a trampoline) and similar
  2670  // machinery in the external linker; see #58425 for more on the
  2671  // history here.
  2672  func splitTextSections(ctxt *Link) bool {
  2673  	return (ctxt.IsARM() || ctxt.IsPPC64() || (ctxt.IsARM64() && ctxt.IsDarwin())) && ctxt.IsExternal()
  2674  }
  2675  
  2676  // On Wasm, we reserve 4096 bytes for zero page, then 8192 bytes for wasm_exec.js
  2677  // to store command line args and environment variables.
  2678  // Data sections starts from at least address 12288.
  2679  // Keep in sync with wasm_exec.js.
  2680  const wasmMinDataAddr = 4096 + 8192
  2681  
  2682  // address assigns virtual addresses to all segments and sections and
  2683  // returns all segments in file order.
  2684  func (ctxt *Link) address() []*sym.Segment {
  2685  	var order []*sym.Segment // Layout order
  2686  
  2687  	va := uint64(*FlagTextAddr)
  2688  	order = append(order, &Segtext)
  2689  	Segtext.Rwx = 05
  2690  	Segtext.Vaddr = va
  2691  	for i, s := range Segtext.Sections {
  2692  		va = uint64(Rnd(int64(va), int64(s.Align)))
  2693  		s.Vaddr = va
  2694  		va += s.Length
  2695  
  2696  		if ctxt.IsWasm() && i == 0 && va < wasmMinDataAddr {
  2697  			va = wasmMinDataAddr
  2698  		}
  2699  	}
  2700  
  2701  	Segtext.Length = va - uint64(*FlagTextAddr)
  2702  
  2703  	if len(Segrodata.Sections) > 0 {
  2704  		// align to page boundary so as not to mix
  2705  		// rodata and executable text.
  2706  		//
  2707  		// Note: gold or GNU ld will reduce the size of the executable
  2708  		// file by arranging for the relro segment to end at a page
  2709  		// boundary, and overlap the end of the text segment with the
  2710  		// start of the relro segment in the file.  The PT_LOAD segments
  2711  		// will be such that the last page of the text segment will be
  2712  		// mapped twice, once r-x and once starting out rw- and, after
  2713  		// relocation processing, changed to r--.
  2714  		//
  2715  		// Ideally the last page of the text segment would not be
  2716  		// writable even for this short period.
  2717  		va = uint64(Rnd(int64(va), *FlagRound))
  2718  
  2719  		order = append(order, &Segrodata)
  2720  		Segrodata.Rwx = 04
  2721  		Segrodata.Vaddr = va
  2722  		for _, s := range Segrodata.Sections {
  2723  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2724  			s.Vaddr = va
  2725  			va += s.Length
  2726  		}
  2727  
  2728  		Segrodata.Length = va - Segrodata.Vaddr
  2729  	}
  2730  	if len(Segrelrodata.Sections) > 0 {
  2731  		// align to page boundary so as not to mix
  2732  		// rodata, rel-ro data, and executable text.
  2733  		va = uint64(Rnd(int64(va), *FlagRound))
  2734  		if ctxt.HeadType == objabi.Haix {
  2735  			// Relro data are inside data segment on AIX.
  2736  			va += uint64(XCOFFDATABASE) - uint64(XCOFFTEXTBASE)
  2737  		}
  2738  
  2739  		order = append(order, &Segrelrodata)
  2740  		Segrelrodata.Rwx = 06
  2741  		Segrelrodata.Vaddr = va
  2742  		for _, s := range Segrelrodata.Sections {
  2743  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2744  			s.Vaddr = va
  2745  			va += s.Length
  2746  		}
  2747  
  2748  		Segrelrodata.Length = va - Segrelrodata.Vaddr
  2749  	}
  2750  
  2751  	va = uint64(Rnd(int64(va), *FlagRound))
  2752  	if ctxt.HeadType == objabi.Haix && len(Segrelrodata.Sections) == 0 {
  2753  		// Data sections are moved to an unreachable segment
  2754  		// to ensure that they are position-independent.
  2755  		// Already done if relro sections exist.
  2756  		va += uint64(XCOFFDATABASE) - uint64(XCOFFTEXTBASE)
  2757  	}
  2758  	order = append(order, &Segdata)
  2759  	Segdata.Rwx = 06
  2760  	Segdata.Vaddr = va
  2761  	var data *sym.Section
  2762  	var noptr *sym.Section
  2763  	var bss *sym.Section
  2764  	var noptrbss *sym.Section
  2765  	var fuzzCounters *sym.Section
  2766  	for i, s := range Segdata.Sections {
  2767  		if (ctxt.IsELF || ctxt.HeadType == objabi.Haix) && s.Name == ".tbss" {
  2768  			continue
  2769  		}
  2770  		vlen := int64(s.Length)
  2771  		if i+1 < len(Segdata.Sections) && !((ctxt.IsELF || ctxt.HeadType == objabi.Haix) && Segdata.Sections[i+1].Name == ".tbss") {
  2772  			vlen = int64(Segdata.Sections[i+1].Vaddr - s.Vaddr)
  2773  		}
  2774  		s.Vaddr = va
  2775  		va += uint64(vlen)
  2776  		Segdata.Length = va - Segdata.Vaddr
  2777  		switch s.Name {
  2778  		case ".data":
  2779  			data = s
  2780  		case ".noptrdata":
  2781  			noptr = s
  2782  		case ".bss":
  2783  			bss = s
  2784  		case ".noptrbss":
  2785  			noptrbss = s
  2786  		case ".go.fuzzcntrs":
  2787  			fuzzCounters = s
  2788  		}
  2789  	}
  2790  
  2791  	// Assign Segdata's Filelen omitting the BSS. We do this here
  2792  	// simply because right now we know where the BSS starts.
  2793  	Segdata.Filelen = bss.Vaddr - Segdata.Vaddr
  2794  
  2795  	if len(Segpdata.Sections) > 0 {
  2796  		va = uint64(Rnd(int64(va), *FlagRound))
  2797  		order = append(order, &Segpdata)
  2798  		Segpdata.Rwx = 04
  2799  		Segpdata.Vaddr = va
  2800  		// Segpdata.Sections is intended to contain just one section.
  2801  		// Loop through the slice anyway for consistency.
  2802  		for _, s := range Segpdata.Sections {
  2803  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2804  			s.Vaddr = va
  2805  			va += s.Length
  2806  		}
  2807  		Segpdata.Length = va - Segpdata.Vaddr
  2808  	}
  2809  
  2810  	if len(Segxdata.Sections) > 0 {
  2811  		va = uint64(Rnd(int64(va), *FlagRound))
  2812  		order = append(order, &Segxdata)
  2813  		Segxdata.Rwx = 04
  2814  		Segxdata.Vaddr = va
  2815  		// Segxdata.Sections is intended to contain just one section.
  2816  		// Loop through the slice anyway for consistency.
  2817  		for _, s := range Segxdata.Sections {
  2818  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2819  			s.Vaddr = va
  2820  			va += s.Length
  2821  		}
  2822  		Segxdata.Length = va - Segxdata.Vaddr
  2823  	}
  2824  
  2825  	va = uint64(Rnd(int64(va), *FlagRound))
  2826  	order = append(order, &Segdwarf)
  2827  	Segdwarf.Rwx = 06
  2828  	Segdwarf.Vaddr = va
  2829  	for i, s := range Segdwarf.Sections {
  2830  		vlen := int64(s.Length)
  2831  		if i+1 < len(Segdwarf.Sections) {
  2832  			vlen = int64(Segdwarf.Sections[i+1].Vaddr - s.Vaddr)
  2833  		}
  2834  		s.Vaddr = va
  2835  		va += uint64(vlen)
  2836  		if ctxt.HeadType == objabi.Hwindows {
  2837  			va = uint64(Rnd(int64(va), PEFILEALIGN))
  2838  		}
  2839  		Segdwarf.Length = va - Segdwarf.Vaddr
  2840  	}
  2841  
  2842  	ldr := ctxt.loader
  2843  	var (
  2844  		rodata  = ldr.SymSect(ldr.LookupOrCreateSym("runtime.rodata", 0))
  2845  		symtab  = ldr.SymSect(ldr.LookupOrCreateSym("runtime.symtab", 0))
  2846  		pclntab = ldr.SymSect(ldr.LookupOrCreateSym("runtime.pclntab", 0))
  2847  		types   = ldr.SymSect(ldr.LookupOrCreateSym("runtime.types", 0))
  2848  	)
  2849  
  2850  	for _, s := range ctxt.datap {
  2851  		if sect := ldr.SymSect(s); sect != nil {
  2852  			ldr.AddToSymValue(s, int64(sect.Vaddr))
  2853  		}
  2854  		v := ldr.SymValue(s)
  2855  		for sub := ldr.SubSym(s); sub != 0; sub = ldr.SubSym(sub) {
  2856  			ldr.AddToSymValue(sub, v)
  2857  		}
  2858  	}
  2859  
  2860  	for _, si := range dwarfp {
  2861  		for _, s := range si.syms {
  2862  			if sect := ldr.SymSect(s); sect != nil {
  2863  				ldr.AddToSymValue(s, int64(sect.Vaddr))
  2864  			}
  2865  			sub := ldr.SubSym(s)
  2866  			if sub != 0 {
  2867  				panic(fmt.Sprintf("unexpected sub-sym for %s %s", ldr.SymName(s), ldr.SymType(s).String()))
  2868  			}
  2869  			v := ldr.SymValue(s)
  2870  			for ; sub != 0; sub = ldr.SubSym(sub) {
  2871  				ldr.AddToSymValue(s, v)
  2872  			}
  2873  		}
  2874  	}
  2875  
  2876  	for _, s := range sehp.pdata {
  2877  		if sect := ldr.SymSect(s); sect != nil {
  2878  			ldr.AddToSymValue(s, int64(sect.Vaddr))
  2879  		}
  2880  	}
  2881  	for _, s := range sehp.xdata {
  2882  		if sect := ldr.SymSect(s); sect != nil {
  2883  			ldr.AddToSymValue(s, int64(sect.Vaddr))
  2884  		}
  2885  	}
  2886  
  2887  	if ctxt.BuildMode == BuildModeShared {
  2888  		s := ldr.LookupOrCreateSym("go:link.abihashbytes", 0)
  2889  		sect := ldr.SymSect(ldr.LookupOrCreateSym(".note.go.abihash", 0))
  2890  		ldr.SetSymSect(s, sect)
  2891  		ldr.SetSymValue(s, int64(sect.Vaddr+16))
  2892  	}
  2893  
  2894  	// If there are multiple text sections, create runtime.text.n for
  2895  	// their section Vaddr, using n for index
  2896  	n := 1
  2897  	for _, sect := range Segtext.Sections[1:] {
  2898  		if sect.Name != ".text" {
  2899  			break
  2900  		}
  2901  		symname := fmt.Sprintf("runtime.text.%d", n)
  2902  		if ctxt.HeadType != objabi.Haix || ctxt.LinkMode != LinkExternal {
  2903  			// Addresses are already set on AIX with external linker
  2904  			// because these symbols are part of their sections.
  2905  			ctxt.xdefine(symname, sym.STEXT, int64(sect.Vaddr))
  2906  		}
  2907  		n++
  2908  	}
  2909  
  2910  	ctxt.xdefine("runtime.rodata", sym.SRODATA, int64(rodata.Vaddr))
  2911  	ctxt.xdefine("runtime.erodata", sym.SRODATA, int64(rodata.Vaddr+rodata.Length))
  2912  	ctxt.xdefine("runtime.types", sym.SRODATA, int64(types.Vaddr))
  2913  	ctxt.xdefine("runtime.etypes", sym.SRODATA, int64(types.Vaddr+types.Length))
  2914  
  2915  	s := ldr.Lookup("runtime.gcdata", 0)
  2916  	ldr.SetAttrLocal(s, true)
  2917  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, ldr.SymAddr(s)+ldr.SymSize(s))
  2918  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.egcdata", 0), ldr.SymSect(s))
  2919  
  2920  	s = ldr.LookupOrCreateSym("runtime.gcbss", 0)
  2921  	ldr.SetAttrLocal(s, true)
  2922  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, ldr.SymAddr(s)+ldr.SymSize(s))
  2923  	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.egcbss", 0), ldr.SymSect(s))
  2924  
  2925  	ctxt.xdefine("runtime.symtab", sym.SRODATA, int64(symtab.Vaddr))
  2926  	ctxt.xdefine("runtime.esymtab", sym.SRODATA, int64(symtab.Vaddr+symtab.Length))
  2927  	ctxt.xdefine("runtime.pclntab", sym.SRODATA, int64(pclntab.Vaddr))
  2928  	ctxt.defineInternal("runtime.pcheader", sym.SRODATA)
  2929  	ctxt.defineInternal("runtime.funcnametab", sym.SRODATA)
  2930  	ctxt.defineInternal("runtime.cutab", sym.SRODATA)
  2931  	ctxt.defineInternal("runtime.filetab", sym.SRODATA)
  2932  	ctxt.defineInternal("runtime.pctab", sym.SRODATA)
  2933  	ctxt.defineInternal("runtime.functab", sym.SRODATA)
  2934  	ctxt.xdefine("runtime.epclntab", sym.SRODATA, int64(pclntab.Vaddr+pclntab.Length))
  2935  	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr))
  2936  	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr+noptr.Length))
  2937  	ctxt.xdefine("runtime.bss", sym.SBSS, int64(bss.Vaddr))
  2938  	ctxt.xdefine("runtime.ebss", sym.SBSS, int64(bss.Vaddr+bss.Length))
  2939  	ctxt.xdefine("runtime.data", sym.SDATA, int64(data.Vaddr))
  2940  	ctxt.xdefine("runtime.edata", sym.SDATA, int64(data.Vaddr+data.Length))
  2941  	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr))
  2942  	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr+noptrbss.Length))
  2943  	ctxt.xdefine("runtime.covctrs", sym.SCOVERAGE_COUNTER, int64(noptrbss.Vaddr+covCounterDataStartOff))
  2944  	ctxt.xdefine("runtime.ecovctrs", sym.SCOVERAGE_COUNTER, int64(noptrbss.Vaddr+covCounterDataStartOff+covCounterDataLen))
  2945  	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
  2946  
  2947  	if fuzzCounters != nil {
  2948  		ctxt.xdefine("runtime.__start___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
  2949  		ctxt.xdefine("runtime.__stop___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
  2950  		ctxt.xdefine("internal/fuzz._counters", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
  2951  		ctxt.xdefine("internal/fuzz._ecounters", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
  2952  	}
  2953  
  2954  	if ctxt.IsSolaris() {
  2955  		// On Solaris, in the runtime it sets the external names of the
  2956  		// end symbols. Unset them and define separate symbols, so we
  2957  		// keep both.
  2958  		etext := ldr.Lookup("runtime.etext", 0)
  2959  		edata := ldr.Lookup("runtime.edata", 0)
  2960  		end := ldr.Lookup("runtime.end", 0)
  2961  		ldr.SetSymExtname(etext, "runtime.etext")
  2962  		ldr.SetSymExtname(edata, "runtime.edata")
  2963  		ldr.SetSymExtname(end, "runtime.end")
  2964  		ctxt.xdefine("_etext", ldr.SymType(etext), ldr.SymValue(etext))
  2965  		ctxt.xdefine("_edata", ldr.SymType(edata), ldr.SymValue(edata))
  2966  		ctxt.xdefine("_end", ldr.SymType(end), ldr.SymValue(end))
  2967  		ldr.SetSymSect(ldr.Lookup("_etext", 0), ldr.SymSect(etext))
  2968  		ldr.SetSymSect(ldr.Lookup("_edata", 0), ldr.SymSect(edata))
  2969  		ldr.SetSymSect(ldr.Lookup("_end", 0), ldr.SymSect(end))
  2970  	}
  2971  
  2972  	if ctxt.IsPPC64() && ctxt.IsElf() {
  2973  		// Resolve .TOC. symbols for all objects. Only one TOC region is supported. If a
  2974  		// GOT section is present, compute it as suggested by the ELFv2 ABI. Otherwise,
  2975  		// choose a similar offset from the start of the data segment.
  2976  		tocAddr := int64(Segdata.Vaddr) + 0x8000
  2977  		if gotAddr := ldr.SymValue(ctxt.GOT); gotAddr != 0 {
  2978  			tocAddr = gotAddr + 0x8000
  2979  		}
  2980  		for i := range ctxt.DotTOC {
  2981  			if i >= sym.SymVerABICount && i < sym.SymVerStatic { // these versions are not used currently
  2982  				continue
  2983  			}
  2984  			if toc := ldr.Lookup(".TOC.", i); toc != 0 {
  2985  				ldr.SetSymValue(toc, tocAddr)
  2986  			}
  2987  		}
  2988  	}
  2989  
  2990  	return order
  2991  }
  2992  
  2993  // layout assigns file offsets and lengths to the segments in order.
  2994  // Returns the file size containing all the segments.
  2995  func (ctxt *Link) layout(order []*sym.Segment) uint64 {
  2996  	var prev *sym.Segment
  2997  	for _, seg := range order {
  2998  		if prev == nil {
  2999  			seg.Fileoff = uint64(HEADR)
  3000  		} else {
  3001  			switch ctxt.HeadType {
  3002  			default:
  3003  				// Assuming the previous segment was
  3004  				// aligned, the following rounding
  3005  				// should ensure that this segment's
  3006  				// VA ≡ Fileoff mod FlagRound.
  3007  				seg.Fileoff = uint64(Rnd(int64(prev.Fileoff+prev.Filelen), *FlagRound))
  3008  				if seg.Vaddr%uint64(*FlagRound) != seg.Fileoff%uint64(*FlagRound) {
  3009  					Exitf("bad segment rounding (Vaddr=%#x Fileoff=%#x FlagRound=%#x)", seg.Vaddr, seg.Fileoff, *FlagRound)
  3010  				}
  3011  			case objabi.Hwindows:
  3012  				seg.Fileoff = prev.Fileoff + uint64(Rnd(int64(prev.Filelen), PEFILEALIGN))
  3013  			case objabi.Hplan9:
  3014  				seg.Fileoff = prev.Fileoff + prev.Filelen
  3015  			}
  3016  		}
  3017  		if seg != &Segdata {
  3018  			// Link.address already set Segdata.Filelen to
  3019  			// account for BSS.
  3020  			seg.Filelen = seg.Length
  3021  		}
  3022  		prev = seg
  3023  	}
  3024  	return prev.Fileoff + prev.Filelen
  3025  }
  3026  
  3027  // add a trampoline with symbol s (to be laid down after the current function)
  3028  func (ctxt *Link) AddTramp(s *loader.SymbolBuilder) {
  3029  	s.SetType(sym.STEXT)
  3030  	s.SetReachable(true)
  3031  	s.SetOnList(true)
  3032  	ctxt.tramps = append(ctxt.tramps, s.Sym())
  3033  	if *FlagDebugTramp > 0 && ctxt.Debugvlog > 0 {
  3034  		ctxt.Logf("trampoline %s inserted\n", s.Name())
  3035  	}
  3036  }
  3037  
  3038  // compressSyms compresses syms and returns the contents of the
  3039  // compressed section. If the section would get larger, it returns nil.
  3040  func compressSyms(ctxt *Link, syms []loader.Sym) []byte {
  3041  	ldr := ctxt.loader
  3042  	var total int64
  3043  	for _, sym := range syms {
  3044  		total += ldr.SymSize(sym)
  3045  	}
  3046  
  3047  	var buf bytes.Buffer
  3048  	if ctxt.IsELF {
  3049  		switch ctxt.Arch.PtrSize {
  3050  		case 8:
  3051  			binary.Write(&buf, ctxt.Arch.ByteOrder, elf.Chdr64{
  3052  				Type:      uint32(elf.COMPRESS_ZLIB),
  3053  				Size:      uint64(total),
  3054  				Addralign: uint64(ctxt.Arch.Alignment),
  3055  			})
  3056  		case 4:
  3057  			binary.Write(&buf, ctxt.Arch.ByteOrder, elf.Chdr32{
  3058  				Type:      uint32(elf.COMPRESS_ZLIB),
  3059  				Size:      uint32(total),
  3060  				Addralign: uint32(ctxt.Arch.Alignment),
  3061  			})
  3062  		default:
  3063  			log.Fatalf("can't compress header size:%d", ctxt.Arch.PtrSize)
  3064  		}
  3065  	} else {
  3066  		buf.Write([]byte("ZLIB"))
  3067  		var sizeBytes [8]byte
  3068  		binary.BigEndian.PutUint64(sizeBytes[:], uint64(total))
  3069  		buf.Write(sizeBytes[:])
  3070  	}
  3071  
  3072  	var relocbuf []byte // temporary buffer for applying relocations
  3073  
  3074  	// Using zlib.BestSpeed achieves very nearly the same
  3075  	// compression levels of zlib.DefaultCompression, but takes
  3076  	// substantially less time. This is important because DWARF
  3077  	// compression can be a significant fraction of link time.
  3078  	z, err := zlib.NewWriterLevel(&buf, zlib.BestSpeed)
  3079  	if err != nil {
  3080  		log.Fatalf("NewWriterLevel failed: %s", err)
  3081  	}
  3082  	st := ctxt.makeRelocSymState()
  3083  	for _, s := range syms {
  3084  		// Symbol data may be read-only. Apply relocations in a
  3085  		// temporary buffer, and immediately write it out.
  3086  		P := ldr.Data(s)
  3087  		relocs := ldr.Relocs(s)
  3088  		if relocs.Count() != 0 {
  3089  			relocbuf = append(relocbuf[:0], P...)
  3090  			P = relocbuf
  3091  			st.relocsym(s, P)
  3092  		}
  3093  		if _, err := z.Write(P); err != nil {
  3094  			log.Fatalf("compression failed: %s", err)
  3095  		}
  3096  		for i := ldr.SymSize(s) - int64(len(P)); i > 0; {
  3097  			b := zeros[:]
  3098  			if i < int64(len(b)) {
  3099  				b = b[:i]
  3100  			}
  3101  			n, err := z.Write(b)
  3102  			if err != nil {
  3103  				log.Fatalf("compression failed: %s", err)
  3104  			}
  3105  			i -= int64(n)
  3106  		}
  3107  	}
  3108  	if err := z.Close(); err != nil {
  3109  		log.Fatalf("compression failed: %s", err)
  3110  	}
  3111  	if int64(buf.Len()) >= total {
  3112  		// Compression didn't save any space.
  3113  		return nil
  3114  	}
  3115  	return buf.Bytes()
  3116  }
  3117  

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