pcln.go

Documentation: cmd/link/internal/ld

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ld
     6  
     7  import (
     8  	"cmd/internal/goobj"
     9  	"cmd/internal/objabi"
    10  	"cmd/internal/sys"
    11  	"cmd/link/internal/loader"
    12  	"cmd/link/internal/sym"
    13  	"fmt"
    14  	"internal/abi"
    15  	"internal/buildcfg"
    16  	"os"
    17  	"path/filepath"
    18  	"strings"
    19  )
    20  
    21  const funcSize = 11 * 4 // funcSize is the size of the _func object in runtime/runtime2.go
    22  
    23  // pclntab holds the state needed for pclntab generation.
    24  type pclntab struct {
    25  	// The first and last functions found.
    26  	firstFunc, lastFunc loader.Sym
    27  
    28  	// Running total size of pclntab.
    29  	size int64
    30  
    31  	// runtime.pclntab's symbols
    32  	carrier     loader.Sym
    33  	pclntab     loader.Sym
    34  	pcheader    loader.Sym
    35  	funcnametab loader.Sym
    36  	findfunctab loader.Sym
    37  	cutab       loader.Sym
    38  	filetab     loader.Sym
    39  	pctab       loader.Sym
    40  
    41  	// The number of functions + number of TEXT sections - 1. This is such an
    42  	// unexpected value because platforms that have more than one TEXT section
    43  	// get a dummy function inserted between because the external linker can place
    44  	// functions in those areas. We mark those areas as not covered by the Go
    45  	// runtime.
    46  	//
    47  	// On most platforms this is the number of reachable functions.
    48  	nfunc int32
    49  
    50  	// The number of filenames in runtime.filetab.
    51  	nfiles uint32
    52  }
    53  
    54  // addGeneratedSym adds a generator symbol to pclntab, returning the new Sym.
    55  // It is the caller's responsibility to save the symbol in state.
    56  func (state *pclntab) addGeneratedSym(ctxt *Link, name string, size int64, f generatorFunc) loader.Sym {
    57  	size = Rnd(size, int64(ctxt.Arch.PtrSize))
    58  	state.size += size
    59  	s := ctxt.createGeneratorSymbol(name, 0, sym.SPCLNTAB, size, f)
    60  	ctxt.loader.SetAttrReachable(s, true)
    61  	ctxt.loader.SetCarrierSym(s, state.carrier)
    62  	ctxt.loader.SetAttrNotInSymbolTable(s, true)
    63  	return s
    64  }
    65  
    66  // makePclntab makes a pclntab object, and assembles all the compilation units
    67  // we'll need to write pclntab. Returns the pclntab structure, a slice of the
    68  // CompilationUnits we need, and a slice of the function symbols we need to
    69  // generate pclntab.
    70  func makePclntab(ctxt *Link, container loader.Bitmap) (*pclntab, []*sym.CompilationUnit, []loader.Sym) {
    71  	ldr := ctxt.loader
    72  	state := new(pclntab)
    73  
    74  	// Gather some basic stats and info.
    75  	seenCUs := make(map[*sym.CompilationUnit]struct{})
    76  	compUnits := []*sym.CompilationUnit{}
    77  	funcs := []loader.Sym{}
    78  
    79  	for _, s := range ctxt.Textp {
    80  		if !emitPcln(ctxt, s, container) {
    81  			continue
    82  		}
    83  		funcs = append(funcs, s)
    84  		state.nfunc++
    85  		if state.firstFunc == 0 {
    86  			state.firstFunc = s
    87  		}
    88  		state.lastFunc = s
    89  
    90  		// We need to keep track of all compilation units we see. Some symbols
    91  		// (eg, go.buildid, _cgoexp_, etc) won't have a compilation unit.
    92  		cu := ldr.SymUnit(s)
    93  		if _, ok := seenCUs[cu]; cu != nil && !ok {
    94  			seenCUs[cu] = struct{}{}
    95  			cu.PclnIndex = len(compUnits)
    96  			compUnits = append(compUnits, cu)
    97  		}
    98  	}
    99  	return state, compUnits, funcs
   100  }
   101  
   102  func emitPcln(ctxt *Link, s loader.Sym, container loader.Bitmap) bool {
   103  	if ctxt.Target.IsRISCV64() {
   104  		// Avoid adding local symbols to the pcln table - RISC-V
   105  		// linking generates a very large number of these, particularly
   106  		// for HI20 symbols (which we need to load in order to be able
   107  		// to resolve relocations). Unnecessarily including all of
   108  		// these symbols quickly blows out the size of the pcln table
   109  		// and overflows hash buckets.
   110  		symName := ctxt.loader.SymName(s)
   111  		if symName == "" || strings.HasPrefix(symName, ".L") {
   112  			return false
   113  		}
   114  	}
   115  
   116  	// We want to generate func table entries only for the "lowest
   117  	// level" symbols, not containers of subsymbols.
   118  	return !container.Has(s)
   119  }
   120  
   121  func computeDeferReturn(ctxt *Link, deferReturnSym, s loader.Sym) uint32 {
   122  	ldr := ctxt.loader
   123  	target := ctxt.Target
   124  	deferreturn := uint32(0)
   125  	lastWasmAddr := uint32(0)
   126  
   127  	relocs := ldr.Relocs(s)
   128  	for ri := 0; ri < relocs.Count(); ri++ {
   129  		r := relocs.At(ri)
   130  		if target.IsWasm() && r.Type() == objabi.R_ADDR {
   131  			// wasm/ssa.go generates an ARESUMEPOINT just
   132  			// before the deferreturn call. The "PC" of
   133  			// the deferreturn call is stored in the
   134  			// R_ADDR relocation on the ARESUMEPOINT.
   135  			lastWasmAddr = uint32(r.Add())
   136  		}
   137  		if r.Type().IsDirectCall() && (r.Sym() == deferReturnSym || ldr.IsDeferReturnTramp(r.Sym())) {
   138  			if target.IsWasm() {
   139  				deferreturn = lastWasmAddr - 1
   140  			} else {
   141  				// Note: the relocation target is in the call instruction, but
   142  				// is not necessarily the whole instruction (for instance, on
   143  				// x86 the relocation applies to bytes [1:5] of the 5 byte call
   144  				// instruction).
   145  				deferreturn = uint32(r.Off())
   146  				switch target.Arch.Family {
   147  				case sys.AMD64, sys.I386:
   148  					deferreturn--
   149  				case sys.ARM, sys.ARM64, sys.Loong64, sys.MIPS, sys.MIPS64, sys.PPC64, sys.RISCV64:
   150  					// no change
   151  				case sys.S390X:
   152  					deferreturn -= 2
   153  				default:
   154  					panic(fmt.Sprint("Unhandled architecture:", target.Arch.Family))
   155  				}
   156  			}
   157  			break // only need one
   158  		}
   159  	}
   160  	return deferreturn
   161  }
   162  
   163  // genInlTreeSym generates the InlTree sym for a function with the
   164  // specified FuncInfo.
   165  func genInlTreeSym(ctxt *Link, cu *sym.CompilationUnit, fi loader.FuncInfo, arch *sys.Arch, nameOffsets map[loader.Sym]uint32) loader.Sym {
   166  	ldr := ctxt.loader
   167  	its := ldr.CreateExtSym("", 0)
   168  	inlTreeSym := ldr.MakeSymbolUpdater(its)
   169  	// Note: the generated symbol is given a type of sym.SGOFUNC, as a
   170  	// signal to the symtab() phase that it needs to be grouped in with
   171  	// other similar symbols (gcdata, etc); the dodata() phase will
   172  	// eventually switch the type back to SRODATA.
   173  	inlTreeSym.SetType(sym.SGOFUNC)
   174  	ldr.SetAttrReachable(its, true)
   175  	ldr.SetSymAlign(its, 4) // it has 32-bit fields
   176  	ninl := fi.NumInlTree()
   177  	for i := 0; i < int(ninl); i++ {
   178  		call := fi.InlTree(i)
   179  		nameOff, ok := nameOffsets[call.Func]
   180  		if !ok {
   181  			panic("couldn't find function name offset")
   182  		}
   183  
   184  		inlFunc := ldr.FuncInfo(call.Func)
   185  		var funcID abi.FuncID
   186  		startLine := int32(0)
   187  		if inlFunc.Valid() {
   188  			funcID = inlFunc.FuncID()
   189  			startLine = inlFunc.StartLine()
   190  		} else if !ctxt.linkShared {
   191  			// Inlined functions are always Go functions, and thus
   192  			// must have FuncInfo.
   193  			//
   194  			// Unfortunately, with -linkshared, the inlined
   195  			// function may be external symbols (from another
   196  			// shared library), and we don't load FuncInfo from the
   197  			// shared library. We will report potentially incorrect
   198  			// FuncID in this case. See https://go.dev/issue/55954.
   199  			panic(fmt.Sprintf("inlined function %s missing func info", ldr.SymName(call.Func)))
   200  		}
   201  
   202  		// Construct runtime.inlinedCall value.
   203  		const size = 16
   204  		inlTreeSym.SetUint8(arch, int64(i*size+0), uint8(funcID))
   205  		// Bytes 1-3 are unused.
   206  		inlTreeSym.SetUint32(arch, int64(i*size+4), uint32(nameOff))
   207  		inlTreeSym.SetUint32(arch, int64(i*size+8), uint32(call.ParentPC))
   208  		inlTreeSym.SetUint32(arch, int64(i*size+12), uint32(startLine))
   209  	}
   210  	return its
   211  }
   212  
   213  // makeInlSyms returns a map of loader.Sym that are created inlSyms.
   214  func makeInlSyms(ctxt *Link, funcs []loader.Sym, nameOffsets map[loader.Sym]uint32) map[loader.Sym]loader.Sym {
   215  	ldr := ctxt.loader
   216  	// Create the inline symbols we need.
   217  	inlSyms := make(map[loader.Sym]loader.Sym)
   218  	for _, s := range funcs {
   219  		if fi := ldr.FuncInfo(s); fi.Valid() {
   220  			fi.Preload()
   221  			if fi.NumInlTree() > 0 {
   222  				inlSyms[s] = genInlTreeSym(ctxt, ldr.SymUnit(s), fi, ctxt.Arch, nameOffsets)
   223  			}
   224  		}
   225  	}
   226  	return inlSyms
   227  }
   228  
   229  // generatePCHeader creates the runtime.pcheader symbol, setting it up as a
   230  // generator to fill in its data later.
   231  func (state *pclntab) generatePCHeader(ctxt *Link) {
   232  	ldr := ctxt.loader
   233  	textStartOff := int64(8 + 2*ctxt.Arch.PtrSize)
   234  	size := int64(8 + 8*ctxt.Arch.PtrSize)
   235  	writeHeader := func(ctxt *Link, s loader.Sym) {
   236  		header := ctxt.loader.MakeSymbolUpdater(s)
   237  
   238  		writeSymOffset := func(off int64, ws loader.Sym) int64 {
   239  			diff := ldr.SymValue(ws) - ldr.SymValue(s)
   240  			if diff <= 0 {
   241  				name := ldr.SymName(ws)
   242  				panic(fmt.Sprintf("expected runtime.pcheader(%x) to be placed before %s(%x)", ldr.SymValue(s), name, ldr.SymValue(ws)))
   243  			}
   244  			return header.SetUintptr(ctxt.Arch, off, uintptr(diff))
   245  		}
   246  
   247  		// Write header.
   248  		// Keep in sync with runtime/symtab.go:pcHeader and package debug/gosym.
   249  		header.SetUint32(ctxt.Arch, 0, 0xfffffff1)
   250  		header.SetUint8(ctxt.Arch, 6, uint8(ctxt.Arch.MinLC))
   251  		header.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
   252  		off := header.SetUint(ctxt.Arch, 8, uint64(state.nfunc))
   253  		off = header.SetUint(ctxt.Arch, off, uint64(state.nfiles))
   254  		if off != textStartOff {
   255  			panic(fmt.Sprintf("pcHeader textStartOff: %d != %d", off, textStartOff))
   256  		}
   257  		off += int64(ctxt.Arch.PtrSize) // skip runtimeText relocation
   258  		off = writeSymOffset(off, state.funcnametab)
   259  		off = writeSymOffset(off, state.cutab)
   260  		off = writeSymOffset(off, state.filetab)
   261  		off = writeSymOffset(off, state.pctab)
   262  		off = writeSymOffset(off, state.pclntab)
   263  		if off != size {
   264  			panic(fmt.Sprintf("pcHeader size: %d != %d", off, size))
   265  		}
   266  	}
   267  
   268  	state.pcheader = state.addGeneratedSym(ctxt, "runtime.pcheader", size, writeHeader)
   269  	// Create the runtimeText relocation.
   270  	sb := ldr.MakeSymbolUpdater(state.pcheader)
   271  	sb.SetAddr(ctxt.Arch, textStartOff, ldr.Lookup("runtime.text", 0))
   272  }
   273  
   274  // walkFuncs iterates over the funcs, calling a function for each unique
   275  // function and inlined function.
   276  func walkFuncs(ctxt *Link, funcs []loader.Sym, f func(loader.Sym)) {
   277  	ldr := ctxt.loader
   278  	seen := make(map[loader.Sym]struct{})
   279  	for _, s := range funcs {
   280  		if _, ok := seen[s]; !ok {
   281  			f(s)
   282  			seen[s] = struct{}{}
   283  		}
   284  
   285  		fi := ldr.FuncInfo(s)
   286  		if !fi.Valid() {
   287  			continue
   288  		}
   289  		fi.Preload()
   290  		for i, ni := 0, fi.NumInlTree(); i < int(ni); i++ {
   291  			call := fi.InlTree(i).Func
   292  			if _, ok := seen[call]; !ok {
   293  				f(call)
   294  				seen[call] = struct{}{}
   295  			}
   296  		}
   297  	}
   298  }
   299  
   300  // generateFuncnametab creates the function name table. Returns a map of
   301  // func symbol to the name offset in runtime.funcnamtab.
   302  func (state *pclntab) generateFuncnametab(ctxt *Link, funcs []loader.Sym) map[loader.Sym]uint32 {
   303  	nameOffsets := make(map[loader.Sym]uint32, state.nfunc)
   304  
   305  	// Write the null terminated strings.
   306  	writeFuncNameTab := func(ctxt *Link, s loader.Sym) {
   307  		symtab := ctxt.loader.MakeSymbolUpdater(s)
   308  		for s, off := range nameOffsets {
   309  			symtab.AddCStringAt(int64(off), ctxt.loader.SymName(s))
   310  		}
   311  	}
   312  
   313  	// Loop through the CUs, and calculate the size needed.
   314  	var size int64
   315  	walkFuncs(ctxt, funcs, func(s loader.Sym) {
   316  		nameOffsets[s] = uint32(size)
   317  		size += int64(len(ctxt.loader.SymName(s)) + 1) // NULL terminate
   318  	})
   319  
   320  	state.funcnametab = state.addGeneratedSym(ctxt, "runtime.funcnametab", size, writeFuncNameTab)
   321  	return nameOffsets
   322  }
   323  
   324  // walkFilenames walks funcs, calling a function for each filename used in each
   325  // function's line table.
   326  func walkFilenames(ctxt *Link, funcs []loader.Sym, f func(*sym.CompilationUnit, goobj.CUFileIndex)) {
   327  	ldr := ctxt.loader
   328  
   329  	// Loop through all functions, finding the filenames we need.
   330  	for _, s := range funcs {
   331  		fi := ldr.FuncInfo(s)
   332  		if !fi.Valid() {
   333  			continue
   334  		}
   335  		fi.Preload()
   336  
   337  		cu := ldr.SymUnit(s)
   338  		for i, nf := 0, int(fi.NumFile()); i < nf; i++ {
   339  			f(cu, fi.File(i))
   340  		}
   341  		for i, ninl := 0, int(fi.NumInlTree()); i < ninl; i++ {
   342  			call := fi.InlTree(i)
   343  			f(cu, call.File)
   344  		}
   345  	}
   346  }
   347  
   348  // generateFilenameTabs creates LUTs needed for filename lookup. Returns a slice
   349  // of the index at which each CU begins in runtime.cutab.
   350  //
   351  // Function objects keep track of the files they reference to print the stack.
   352  // This function creates a per-CU list of filenames if CU[M] references
   353  // files[1-N], the following is generated:
   354  //
   355  //	runtime.cutab:
   356  //	  CU[M]
   357  //	   offsetToFilename[0]
   358  //	   offsetToFilename[1]
   359  //	   ..
   360  //
   361  //	runtime.filetab
   362  //	   filename[0]
   363  //	   filename[1]
   364  //
   365  // Looking up a filename then becomes:
   366  //  0. Given a func, and filename index [K]
   367  //  1. Get Func.CUIndex:       M := func.cuOffset
   368  //  2. Find filename offset:   fileOffset := runtime.cutab[M+K]
   369  //  3. Get the filename:       getcstring(runtime.filetab[fileOffset])
   370  func (state *pclntab) generateFilenameTabs(ctxt *Link, compUnits []*sym.CompilationUnit, funcs []loader.Sym) []uint32 {
   371  	// On a per-CU basis, keep track of all the filenames we need.
   372  	//
   373  	// Note, that we store the filenames in a separate section in the object
   374  	// files, and deduplicate based on the actual value. It would be better to
   375  	// store the filenames as symbols, using content addressable symbols (and
   376  	// then not loading extra filenames), and just use the hash value of the
   377  	// symbol name to do this cataloging.
   378  	//
   379  	// TODO: Store filenames as symbols. (Note this would be easiest if you
   380  	// also move strings to ALWAYS using the larger content addressable hash
   381  	// function, and use that hash value for uniqueness testing.)
   382  	cuEntries := make([]goobj.CUFileIndex, len(compUnits))
   383  	fileOffsets := make(map[string]uint32)
   384  
   385  	// Walk the filenames.
   386  	// We store the total filename string length we need to load, and the max
   387  	// file index we've seen per CU so we can calculate how large the
   388  	// CU->global table needs to be.
   389  	var fileSize int64
   390  	walkFilenames(ctxt, funcs, func(cu *sym.CompilationUnit, i goobj.CUFileIndex) {
   391  		// Note we use the raw filename for lookup, but use the expanded filename
   392  		// when we save the size.
   393  		filename := cu.FileTable[i]
   394  		if _, ok := fileOffsets[filename]; !ok {
   395  			fileOffsets[filename] = uint32(fileSize)
   396  			fileSize += int64(len(expandFile(filename)) + 1) // NULL terminate
   397  		}
   398  
   399  		// Find the maximum file index we've seen.
   400  		if cuEntries[cu.PclnIndex] < i+1 {
   401  			cuEntries[cu.PclnIndex] = i + 1 // Store max + 1
   402  		}
   403  	})
   404  
   405  	// Calculate the size of the runtime.cutab variable.
   406  	var totalEntries uint32
   407  	cuOffsets := make([]uint32, len(cuEntries))
   408  	for i, entries := range cuEntries {
   409  		// Note, cutab is a slice of uint32, so an offset to a cu's entry is just the
   410  		// running total of all cu indices we've needed to store so far, not the
   411  		// number of bytes we've stored so far.
   412  		cuOffsets[i] = totalEntries
   413  		totalEntries += uint32(entries)
   414  	}
   415  
   416  	// Write cutab.
   417  	writeCutab := func(ctxt *Link, s loader.Sym) {
   418  		sb := ctxt.loader.MakeSymbolUpdater(s)
   419  
   420  		var off int64
   421  		for i, max := range cuEntries {
   422  			// Write the per CU LUT.
   423  			cu := compUnits[i]
   424  			for j := goobj.CUFileIndex(0); j < max; j++ {
   425  				fileOffset, ok := fileOffsets[cu.FileTable[j]]
   426  				if !ok {
   427  					// We're looping through all possible file indices. It's possible a file's
   428  					// been deadcode eliminated, and although it's a valid file in the CU, it's
   429  					// not needed in this binary. When that happens, use an invalid offset.
   430  					fileOffset = ^uint32(0)
   431  				}
   432  				off = sb.SetUint32(ctxt.Arch, off, fileOffset)
   433  			}
   434  		}
   435  	}
   436  	state.cutab = state.addGeneratedSym(ctxt, "runtime.cutab", int64(totalEntries*4), writeCutab)
   437  
   438  	// Write filetab.
   439  	writeFiletab := func(ctxt *Link, s loader.Sym) {
   440  		sb := ctxt.loader.MakeSymbolUpdater(s)
   441  
   442  		// Write the strings.
   443  		for filename, loc := range fileOffsets {
   444  			sb.AddStringAt(int64(loc), expandFile(filename))
   445  		}
   446  	}
   447  	state.nfiles = uint32(len(fileOffsets))
   448  	state.filetab = state.addGeneratedSym(ctxt, "runtime.filetab", fileSize, writeFiletab)
   449  
   450  	return cuOffsets
   451  }
   452  
   453  // generatePctab creates the runtime.pctab variable, holding all the
   454  // deduplicated pcdata.
   455  func (state *pclntab) generatePctab(ctxt *Link, funcs []loader.Sym) {
   456  	ldr := ctxt.loader
   457  
   458  	// Pctab offsets of 0 are considered invalid in the runtime. We respect
   459  	// that by just padding a single byte at the beginning of runtime.pctab,
   460  	// that way no real offsets can be zero.
   461  	size := int64(1)
   462  
   463  	// Walk the functions, finding offset to store each pcdata.
   464  	seen := make(map[loader.Sym]struct{})
   465  	saveOffset := func(pcSym loader.Sym) {
   466  		if _, ok := seen[pcSym]; !ok {
   467  			datSize := ldr.SymSize(pcSym)
   468  			if datSize != 0 {
   469  				ldr.SetSymValue(pcSym, size)
   470  			} else {
   471  				// Invalid PC data, record as zero.
   472  				ldr.SetSymValue(pcSym, 0)
   473  			}
   474  			size += datSize
   475  			seen[pcSym] = struct{}{}
   476  		}
   477  	}
   478  	var pcsp, pcline, pcfile, pcinline loader.Sym
   479  	var pcdata []loader.Sym
   480  	for _, s := range funcs {
   481  		fi := ldr.FuncInfo(s)
   482  		if !fi.Valid() {
   483  			continue
   484  		}
   485  		fi.Preload()
   486  		pcsp, pcfile, pcline, pcinline, pcdata = ldr.PcdataAuxs(s, pcdata)
   487  
   488  		pcSyms := []loader.Sym{pcsp, pcfile, pcline}
   489  		for _, pcSym := range pcSyms {
   490  			saveOffset(pcSym)
   491  		}
   492  		for _, pcSym := range pcdata {
   493  			saveOffset(pcSym)
   494  		}
   495  		if fi.NumInlTree() > 0 {
   496  			saveOffset(pcinline)
   497  		}
   498  	}
   499  
   500  	// TODO: There is no reason we need a generator for this variable, and it
   501  	// could be moved to a carrier symbol. However, carrier symbols containing
   502  	// carrier symbols don't work yet (as of Aug 2020). Once this is fixed,
   503  	// runtime.pctab could just be a carrier sym.
   504  	writePctab := func(ctxt *Link, s loader.Sym) {
   505  		ldr := ctxt.loader
   506  		sb := ldr.MakeSymbolUpdater(s)
   507  		for sym := range seen {
   508  			sb.SetBytesAt(ldr.SymValue(sym), ldr.Data(sym))
   509  		}
   510  	}
   511  
   512  	state.pctab = state.addGeneratedSym(ctxt, "runtime.pctab", size, writePctab)
   513  }
   514  
   515  // numPCData returns the number of PCData syms for the FuncInfo.
   516  // NB: Preload must be called on valid FuncInfos before calling this function.
   517  func numPCData(ldr *loader.Loader, s loader.Sym, fi loader.FuncInfo) uint32 {
   518  	if !fi.Valid() {
   519  		return 0
   520  	}
   521  	numPCData := uint32(ldr.NumPcdata(s))
   522  	if fi.NumInlTree() > 0 {
   523  		if numPCData < abi.PCDATA_InlTreeIndex+1 {
   524  			numPCData = abi.PCDATA_InlTreeIndex + 1
   525  		}
   526  	}
   527  	return numPCData
   528  }
   529  
   530  // generateFunctab creates the runtime.functab
   531  //
   532  // runtime.functab contains two things:
   533  //
   534  //   - pc->func look up table.
   535  //   - array of func objects, interleaved with pcdata and funcdata
   536  func (state *pclntab) generateFunctab(ctxt *Link, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
   537  	// Calculate the size of the table.
   538  	size, startLocations := state.calculateFunctabSize(ctxt, funcs)
   539  	writePcln := func(ctxt *Link, s loader.Sym) {
   540  		ldr := ctxt.loader
   541  		sb := ldr.MakeSymbolUpdater(s)
   542  		// Write the data.
   543  		writePCToFunc(ctxt, sb, funcs, startLocations)
   544  		writeFuncs(ctxt, sb, funcs, inlSyms, startLocations, cuOffsets, nameOffsets)
   545  	}
   546  	state.pclntab = state.addGeneratedSym(ctxt, "runtime.functab", size, writePcln)
   547  }
   548  
   549  // funcData returns the funcdata and offsets for the FuncInfo.
   550  // The funcdata are written into runtime.functab after each func
   551  // object. This is a helper function to make querying the FuncInfo object
   552  // cleaner.
   553  //
   554  // NB: Preload must be called on the FuncInfo before calling.
   555  // NB: fdSyms is used as scratch space.
   556  func funcData(ldr *loader.Loader, s loader.Sym, fi loader.FuncInfo, inlSym loader.Sym, fdSyms []loader.Sym) []loader.Sym {
   557  	fdSyms = fdSyms[:0]
   558  	if fi.Valid() {
   559  		fdSyms = ldr.Funcdata(s, fdSyms)
   560  		if fi.NumInlTree() > 0 {
   561  			if len(fdSyms) < abi.FUNCDATA_InlTree+1 {
   562  				fdSyms = append(fdSyms, make([]loader.Sym, abi.FUNCDATA_InlTree+1-len(fdSyms))...)
   563  			}
   564  			fdSyms[abi.FUNCDATA_InlTree] = inlSym
   565  		}
   566  	}
   567  	return fdSyms
   568  }
   569  
   570  // calculateFunctabSize calculates the size of the pclntab, and the offsets in
   571  // the output buffer for individual func entries.
   572  func (state pclntab) calculateFunctabSize(ctxt *Link, funcs []loader.Sym) (int64, []uint32) {
   573  	ldr := ctxt.loader
   574  	startLocations := make([]uint32, len(funcs))
   575  
   576  	// Allocate space for the pc->func table. This structure consists of a pc offset
   577  	// and an offset to the func structure. After that, we have a single pc
   578  	// value that marks the end of the last function in the binary.
   579  	size := int64(int(state.nfunc)*2*4 + 4)
   580  
   581  	// Now find the space for the func objects. We do this in a running manner,
   582  	// so that we can find individual starting locations.
   583  	for i, s := range funcs {
   584  		size = Rnd(size, int64(ctxt.Arch.PtrSize))
   585  		startLocations[i] = uint32(size)
   586  		fi := ldr.FuncInfo(s)
   587  		size += funcSize
   588  		if fi.Valid() {
   589  			fi.Preload()
   590  			numFuncData := ldr.NumFuncdata(s)
   591  			if fi.NumInlTree() > 0 {
   592  				if numFuncData < abi.FUNCDATA_InlTree+1 {
   593  					numFuncData = abi.FUNCDATA_InlTree + 1
   594  				}
   595  			}
   596  			size += int64(numPCData(ldr, s, fi) * 4)
   597  			size += int64(numFuncData * 4)
   598  		}
   599  	}
   600  
   601  	return size, startLocations
   602  }
   603  
   604  // writePCToFunc writes the PC->func lookup table.
   605  func writePCToFunc(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, startLocations []uint32) {
   606  	ldr := ctxt.loader
   607  	textStart := ldr.SymValue(ldr.Lookup("runtime.text", 0))
   608  	pcOff := func(s loader.Sym) uint32 {
   609  		off := ldr.SymValue(s) - textStart
   610  		if off < 0 {
   611  			panic(fmt.Sprintf("expected func %s(%x) to be placed at or after textStart (%x)", ldr.SymName(s), ldr.SymValue(s), textStart))
   612  		}
   613  		return uint32(off)
   614  	}
   615  	for i, s := range funcs {
   616  		sb.SetUint32(ctxt.Arch, int64(i*2*4), pcOff(s))
   617  		sb.SetUint32(ctxt.Arch, int64((i*2+1)*4), startLocations[i])
   618  	}
   619  
   620  	// Final entry of table is just end pc offset.
   621  	lastFunc := funcs[len(funcs)-1]
   622  	sb.SetUint32(ctxt.Arch, int64(len(funcs))*2*4, pcOff(lastFunc)+uint32(ldr.SymSize(lastFunc)))
   623  }
   624  
   625  // writeFuncs writes the func structures and pcdata to runtime.functab.
   626  func writeFuncs(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, startLocations, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
   627  	ldr := ctxt.loader
   628  	deferReturnSym := ldr.Lookup("runtime.deferreturn", abiInternalVer)
   629  	gofunc := ldr.Lookup("go:func.*", 0)
   630  	gofuncBase := ldr.SymValue(gofunc)
   631  	textStart := ldr.SymValue(ldr.Lookup("runtime.text", 0))
   632  	funcdata := []loader.Sym{}
   633  	var pcsp, pcfile, pcline, pcinline loader.Sym
   634  	var pcdata []loader.Sym
   635  
   636  	// Write the individual func objects.
   637  	for i, s := range funcs {
   638  		startLine := int32(0)
   639  		fi := ldr.FuncInfo(s)
   640  		if fi.Valid() {
   641  			fi.Preload()
   642  			pcsp, pcfile, pcline, pcinline, pcdata = ldr.PcdataAuxs(s, pcdata)
   643  			startLine = fi.StartLine()
   644  		}
   645  
   646  		off := int64(startLocations[i])
   647  		// entryOff uint32 (offset of func entry PC from textStart)
   648  		entryOff := ldr.SymValue(s) - textStart
   649  		if entryOff < 0 {
   650  			panic(fmt.Sprintf("expected func %s(%x) to be placed before or at textStart (%x)", ldr.SymName(s), ldr.SymValue(s), textStart))
   651  		}
   652  		off = sb.SetUint32(ctxt.Arch, off, uint32(entryOff))
   653  
   654  		// nameOff int32
   655  		nameOff, ok := nameOffsets[s]
   656  		if !ok {
   657  			panic("couldn't find function name offset")
   658  		}
   659  		off = sb.SetUint32(ctxt.Arch, off, uint32(nameOff))
   660  
   661  		// args int32
   662  		// TODO: Move into funcinfo.
   663  		args := uint32(0)
   664  		if fi.Valid() {
   665  			args = uint32(fi.Args())
   666  		}
   667  		off = sb.SetUint32(ctxt.Arch, off, args)
   668  
   669  		// deferreturn
   670  		deferreturn := computeDeferReturn(ctxt, deferReturnSym, s)
   671  		off = sb.SetUint32(ctxt.Arch, off, deferreturn)
   672  
   673  		// pcdata
   674  		if fi.Valid() {
   675  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcsp)))
   676  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcfile)))
   677  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcline)))
   678  		} else {
   679  			off += 12
   680  		}
   681  		off = sb.SetUint32(ctxt.Arch, off, uint32(numPCData(ldr, s, fi)))
   682  
   683  		// Store the offset to compilation unit's file table.
   684  		cuIdx := ^uint32(0)
   685  		if cu := ldr.SymUnit(s); cu != nil {
   686  			cuIdx = cuOffsets[cu.PclnIndex]
   687  		}
   688  		off = sb.SetUint32(ctxt.Arch, off, cuIdx)
   689  
   690  		// startLine int32
   691  		off = sb.SetUint32(ctxt.Arch, off, uint32(startLine))
   692  
   693  		// funcID uint8
   694  		var funcID abi.FuncID
   695  		if fi.Valid() {
   696  			funcID = fi.FuncID()
   697  		}
   698  		off = sb.SetUint8(ctxt.Arch, off, uint8(funcID))
   699  
   700  		// flag uint8
   701  		var flag abi.FuncFlag
   702  		if fi.Valid() {
   703  			flag = fi.FuncFlag()
   704  		}
   705  		off = sb.SetUint8(ctxt.Arch, off, uint8(flag))
   706  
   707  		off += 1 // pad
   708  
   709  		// nfuncdata must be the final entry.
   710  		funcdata = funcData(ldr, s, fi, 0, funcdata)
   711  		off = sb.SetUint8(ctxt.Arch, off, uint8(len(funcdata)))
   712  
   713  		// Output the pcdata.
   714  		if fi.Valid() {
   715  			for j, pcSym := range pcdata {
   716  				sb.SetUint32(ctxt.Arch, off+int64(j*4), uint32(ldr.SymValue(pcSym)))
   717  			}
   718  			if fi.NumInlTree() > 0 {
   719  				sb.SetUint32(ctxt.Arch, off+abi.PCDATA_InlTreeIndex*4, uint32(ldr.SymValue(pcinline)))
   720  			}
   721  		}
   722  
   723  		// Write funcdata refs as offsets from go:func.* and go:funcrel.*.
   724  		funcdata = funcData(ldr, s, fi, inlSyms[s], funcdata)
   725  		// Missing funcdata will be ^0. See runtime/symtab.go:funcdata.
   726  		off = int64(startLocations[i] + funcSize + numPCData(ldr, s, fi)*4)
   727  		for j := range funcdata {
   728  			dataoff := off + int64(4*j)
   729  			fdsym := funcdata[j]
   730  
   731  			// cmd/internal/obj optimistically populates ArgsPointerMaps and
   732  			// ArgInfo for assembly functions, hoping that the compiler will
   733  			// emit appropriate symbols from their Go stub declarations. If
   734  			// it didn't though, just ignore it.
   735  			//
   736  			// TODO(cherryyz): Fix arg map generation (see discussion on CL 523335).
   737  			if fdsym != 0 && (j == abi.FUNCDATA_ArgsPointerMaps || j == abi.FUNCDATA_ArgInfo) && ldr.IsFromAssembly(s) && ldr.Data(fdsym) == nil {
   738  				fdsym = 0
   739  			}
   740  
   741  			if fdsym == 0 {
   742  				sb.SetUint32(ctxt.Arch, dataoff, ^uint32(0)) // ^0 is a sentinel for "no value"
   743  				continue
   744  			}
   745  
   746  			if outer := ldr.OuterSym(fdsym); outer != gofunc {
   747  				panic(fmt.Sprintf("bad carrier sym for symbol %s (funcdata %s#%d), want go:func.* got %s", ldr.SymName(fdsym), ldr.SymName(s), j, ldr.SymName(outer)))
   748  			}
   749  			sb.SetUint32(ctxt.Arch, dataoff, uint32(ldr.SymValue(fdsym)-gofuncBase))
   750  		}
   751  	}
   752  }
   753  
   754  // pclntab initializes the pclntab symbol with
   755  // runtime function and file name information.
   756  
   757  // pclntab generates the pcln table for the link output.
   758  func (ctxt *Link) pclntab(container loader.Bitmap) *pclntab {
   759  	// Go 1.2's symtab layout is documented in golang.org/s/go12symtab, but the
   760  	// layout and data has changed since that time.
   761  	//
   762  	// As of August 2020, here's the layout of pclntab:
   763  	//
   764  	//  .gopclntab/__gopclntab [elf/macho section]
   765  	//    runtime.pclntab
   766  	//      Carrier symbol for the entire pclntab section.
   767  	//
   768  	//      runtime.pcheader  (see: runtime/symtab.go:pcHeader)
   769  	//        8-byte magic
   770  	//        nfunc [thearch.ptrsize bytes]
   771  	//        offset to runtime.funcnametab from the beginning of runtime.pcheader
   772  	//        offset to runtime.pclntab_old from beginning of runtime.pcheader
   773  	//
   774  	//      runtime.funcnametab
   775  	//        []list of null terminated function names
   776  	//
   777  	//      runtime.cutab
   778  	//        for i=0..#CUs
   779  	//          for j=0..#max used file index in CU[i]
   780  	//            uint32 offset into runtime.filetab for the filename[j]
   781  	//
   782  	//      runtime.filetab
   783  	//        []null terminated filename strings
   784  	//
   785  	//      runtime.pctab
   786  	//        []byte of deduplicated pc data.
   787  	//
   788  	//      runtime.functab
   789  	//        function table, alternating PC and offset to func struct [each entry thearch.ptrsize bytes]
   790  	//        end PC [thearch.ptrsize bytes]
   791  	//        func structures, pcdata offsets, func data.
   792  
   793  	state, compUnits, funcs := makePclntab(ctxt, container)
   794  
   795  	ldr := ctxt.loader
   796  	state.carrier = ldr.LookupOrCreateSym("runtime.pclntab", 0)
   797  	ldr.MakeSymbolUpdater(state.carrier).SetType(sym.SPCLNTAB)
   798  	ldr.SetAttrReachable(state.carrier, true)
   799  	setCarrierSym(sym.SPCLNTAB, state.carrier)
   800  
   801  	state.generatePCHeader(ctxt)
   802  	nameOffsets := state.generateFuncnametab(ctxt, funcs)
   803  	cuOffsets := state.generateFilenameTabs(ctxt, compUnits, funcs)
   804  	state.generatePctab(ctxt, funcs)
   805  	inlSyms := makeInlSyms(ctxt, funcs, nameOffsets)
   806  	state.generateFunctab(ctxt, funcs, inlSyms, cuOffsets, nameOffsets)
   807  
   808  	return state
   809  }
   810  
   811  func gorootFinal() string {
   812  	root := buildcfg.GOROOT
   813  	if final := os.Getenv("GOROOT_FINAL"); final != "" {
   814  		root = final
   815  	}
   816  	return root
   817  }
   818  
   819  func expandGoroot(s string) string {
   820  	const n = len("$GOROOT")
   821  	if len(s) >= n+1 && s[:n] == "$GOROOT" && (s[n] == '/' || s[n] == '\\') {
   822  		if final := gorootFinal(); final != "" {
   823  			return filepath.ToSlash(filepath.Join(final, s[n:]))
   824  		}
   825  	}
   826  	return s
   827  }
   828  
   829  const (
   830  	BUCKETSIZE    = 256 * MINFUNC
   831  	SUBBUCKETS    = 16
   832  	SUBBUCKETSIZE = BUCKETSIZE / SUBBUCKETS
   833  	NOIDX         = 0x7fffffff
   834  )
   835  
   836  // findfunctab generates a lookup table to quickly find the containing
   837  // function for a pc. See src/runtime/symtab.go:findfunc for details.
   838  func (ctxt *Link) findfunctab(state *pclntab, container loader.Bitmap) {
   839  	ldr := ctxt.loader
   840  
   841  	// find min and max address
   842  	min := ldr.SymValue(ctxt.Textp[0])
   843  	lastp := ctxt.Textp[len(ctxt.Textp)-1]
   844  	max := ldr.SymValue(lastp) + ldr.SymSize(lastp)
   845  
   846  	// for each subbucket, compute the minimum of all symbol indexes
   847  	// that map to that subbucket.
   848  	n := int32((max - min + SUBBUCKETSIZE - 1) / SUBBUCKETSIZE)
   849  
   850  	nbuckets := int32((max - min + BUCKETSIZE - 1) / BUCKETSIZE)
   851  
   852  	size := 4*int64(nbuckets) + int64(n)
   853  
   854  	writeFindFuncTab := func(_ *Link, s loader.Sym) {
   855  		t := ldr.MakeSymbolUpdater(s)
   856  
   857  		indexes := make([]int32, n)
   858  		for i := int32(0); i < n; i++ {
   859  			indexes[i] = NOIDX
   860  		}
   861  		idx := int32(0)
   862  		for i, s := range ctxt.Textp {
   863  			if !emitPcln(ctxt, s, container) {
   864  				continue
   865  			}
   866  			p := ldr.SymValue(s)
   867  			var e loader.Sym
   868  			i++
   869  			if i < len(ctxt.Textp) {
   870  				e = ctxt.Textp[i]
   871  			}
   872  			for e != 0 && !emitPcln(ctxt, e, container) && i < len(ctxt.Textp) {
   873  				e = ctxt.Textp[i]
   874  				i++
   875  			}
   876  			q := max
   877  			if e != 0 {
   878  				q = ldr.SymValue(e)
   879  			}
   880  
   881  			//print("%d: [%lld %lld] %s\n", idx, p, q, s->name);
   882  			for ; p < q; p += SUBBUCKETSIZE {
   883  				i = int((p - min) / SUBBUCKETSIZE)
   884  				if indexes[i] > idx {
   885  					indexes[i] = idx
   886  				}
   887  			}
   888  
   889  			i = int((q - 1 - min) / SUBBUCKETSIZE)
   890  			if indexes[i] > idx {
   891  				indexes[i] = idx
   892  			}
   893  			idx++
   894  		}
   895  
   896  		// fill in table
   897  		for i := int32(0); i < nbuckets; i++ {
   898  			base := indexes[i*SUBBUCKETS]
   899  			if base == NOIDX {
   900  				Errorf(nil, "hole in findfunctab")
   901  			}
   902  			t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
   903  			for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
   904  				idx = indexes[i*SUBBUCKETS+j]
   905  				if idx == NOIDX {
   906  					Errorf(nil, "hole in findfunctab")
   907  				}
   908  				if idx-base >= 256 {
   909  					Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
   910  				}
   911  
   912  				t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
   913  			}
   914  		}
   915  	}
   916  
   917  	state.findfunctab = ctxt.createGeneratorSymbol("runtime.findfunctab", 0, sym.SRODATA, size, writeFindFuncTab)
   918  	ldr.SetAttrReachable(state.findfunctab, true)
   919  	ldr.SetAttrLocal(state.findfunctab, true)
   920  }
   921  
   922  // findContainerSyms returns a bitmap, indexed by symbol number, where there's
   923  // a 1 for every container symbol.
   924  func (ctxt *Link) findContainerSyms() loader.Bitmap {
   925  	ldr := ctxt.loader
   926  	container := loader.MakeBitmap(ldr.NSym())
   927  	// Find container symbols and mark them as such.
   928  	for _, s := range ctxt.Textp {
   929  		outer := ldr.OuterSym(s)
   930  		if outer != 0 {
   931  			container.Set(outer)
   932  		}
   933  	}
   934  	return container
   935  }
   936
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