sym.go

Documentation: cmd/internal/obj

     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 obj
    33  
    34  import (
    35  	"cmd/internal/goobj"
    36  	"cmd/internal/notsha256"
    37  	"cmd/internal/objabi"
    38  	"encoding/base64"
    39  	"encoding/binary"
    40  	"fmt"
    41  	"internal/buildcfg"
    42  	"log"
    43  	"math"
    44  	"sort"
    45  )
    46  
    47  func Linknew(arch *LinkArch) *Link {
    48  	ctxt := new(Link)
    49  	ctxt.hash = make(map[string]*LSym)
    50  	ctxt.funchash = make(map[string]*LSym)
    51  	ctxt.statichash = make(map[string]*LSym)
    52  	ctxt.Arch = arch
    53  	ctxt.Pathname = objabi.WorkingDir()
    54  
    55  	if err := ctxt.Headtype.Set(buildcfg.GOOS); err != nil {
    56  		log.Fatalf("unknown goos %s", buildcfg.GOOS)
    57  	}
    58  
    59  	ctxt.Flag_optimize = true
    60  	return ctxt
    61  }
    62  
    63  // LookupDerived looks up or creates the symbol with name derived from symbol s.
    64  // The resulting symbol will be static iff s is.
    65  func (ctxt *Link) LookupDerived(s *LSym, name string) *LSym {
    66  	if s.Static() {
    67  		return ctxt.LookupStatic(name)
    68  	}
    69  	return ctxt.Lookup(name)
    70  }
    71  
    72  // LookupStatic looks up the static symbol with name name.
    73  // If it does not exist, it creates it.
    74  func (ctxt *Link) LookupStatic(name string) *LSym {
    75  	s := ctxt.statichash[name]
    76  	if s == nil {
    77  		s = &LSym{Name: name, Attribute: AttrStatic}
    78  		ctxt.statichash[name] = s
    79  	}
    80  	return s
    81  }
    82  
    83  // LookupABI looks up a symbol with the given ABI.
    84  // If it does not exist, it creates it.
    85  func (ctxt *Link) LookupABI(name string, abi ABI) *LSym {
    86  	return ctxt.LookupABIInit(name, abi, nil)
    87  }
    88  
    89  // LookupABIInit looks up a symbol with the given ABI.
    90  // If it does not exist, it creates it and
    91  // passes it to init for one-time initialization.
    92  func (ctxt *Link) LookupABIInit(name string, abi ABI, init func(s *LSym)) *LSym {
    93  	var hash map[string]*LSym
    94  	switch abi {
    95  	case ABI0:
    96  		hash = ctxt.hash
    97  	case ABIInternal:
    98  		hash = ctxt.funchash
    99  	default:
   100  		panic("unknown ABI")
   101  	}
   102  
   103  	ctxt.hashmu.Lock()
   104  	s := hash[name]
   105  	if s == nil {
   106  		s = &LSym{Name: name}
   107  		s.SetABI(abi)
   108  		hash[name] = s
   109  		if init != nil {
   110  			init(s)
   111  		}
   112  	}
   113  	ctxt.hashmu.Unlock()
   114  	return s
   115  }
   116  
   117  // Lookup looks up the symbol with name name.
   118  // If it does not exist, it creates it.
   119  func (ctxt *Link) Lookup(name string) *LSym {
   120  	return ctxt.LookupInit(name, nil)
   121  }
   122  
   123  // LookupInit looks up the symbol with name name.
   124  // If it does not exist, it creates it and
   125  // passes it to init for one-time initialization.
   126  func (ctxt *Link) LookupInit(name string, init func(s *LSym)) *LSym {
   127  	ctxt.hashmu.Lock()
   128  	s := ctxt.hash[name]
   129  	if s == nil {
   130  		s = &LSym{Name: name}
   131  		ctxt.hash[name] = s
   132  		if init != nil {
   133  			init(s)
   134  		}
   135  	}
   136  	ctxt.hashmu.Unlock()
   137  	return s
   138  }
   139  
   140  func (ctxt *Link) Float32Sym(f float32) *LSym {
   141  	i := math.Float32bits(f)
   142  	name := fmt.Sprintf("$f32.%08x", i)
   143  	return ctxt.LookupInit(name, func(s *LSym) {
   144  		s.Size = 4
   145  		s.WriteFloat32(ctxt, 0, f)
   146  		s.Type = objabi.SRODATA
   147  		s.Set(AttrLocal, true)
   148  		s.Set(AttrContentAddressable, true)
   149  		ctxt.constSyms = append(ctxt.constSyms, s)
   150  	})
   151  }
   152  
   153  func (ctxt *Link) Float64Sym(f float64) *LSym {
   154  	i := math.Float64bits(f)
   155  	name := fmt.Sprintf("$f64.%016x", i)
   156  	return ctxt.LookupInit(name, func(s *LSym) {
   157  		s.Size = 8
   158  		s.WriteFloat64(ctxt, 0, f)
   159  		s.Type = objabi.SRODATA
   160  		s.Set(AttrLocal, true)
   161  		s.Set(AttrContentAddressable, true)
   162  		ctxt.constSyms = append(ctxt.constSyms, s)
   163  	})
   164  }
   165  
   166  func (ctxt *Link) Int32Sym(i int64) *LSym {
   167  	name := fmt.Sprintf("$i32.%08x", uint64(i))
   168  	return ctxt.LookupInit(name, func(s *LSym) {
   169  		s.Size = 4
   170  		s.WriteInt(ctxt, 0, 4, i)
   171  		s.Type = objabi.SRODATA
   172  		s.Set(AttrLocal, true)
   173  		s.Set(AttrContentAddressable, true)
   174  		ctxt.constSyms = append(ctxt.constSyms, s)
   175  	})
   176  }
   177  
   178  func (ctxt *Link) Int64Sym(i int64) *LSym {
   179  	name := fmt.Sprintf("$i64.%016x", uint64(i))
   180  	return ctxt.LookupInit(name, func(s *LSym) {
   181  		s.Size = 8
   182  		s.WriteInt(ctxt, 0, 8, i)
   183  		s.Type = objabi.SRODATA
   184  		s.Set(AttrLocal, true)
   185  		s.Set(AttrContentAddressable, true)
   186  		ctxt.constSyms = append(ctxt.constSyms, s)
   187  	})
   188  }
   189  
   190  func (ctxt *Link) Int128Sym(hi, lo int64) *LSym {
   191  	name := fmt.Sprintf("$i128.%016x%016x", uint64(hi), uint64(lo))
   192  	return ctxt.LookupInit(name, func(s *LSym) {
   193  		s.Size = 16
   194  		if ctxt.Arch.ByteOrder == binary.LittleEndian {
   195  			s.WriteInt(ctxt, 0, 8, lo)
   196  			s.WriteInt(ctxt, 8, 8, hi)
   197  		} else {
   198  			s.WriteInt(ctxt, 0, 8, hi)
   199  			s.WriteInt(ctxt, 8, 8, lo)
   200  		}
   201  		s.Type = objabi.SRODATA
   202  		s.Set(AttrLocal, true)
   203  		s.Set(AttrContentAddressable, true)
   204  		ctxt.constSyms = append(ctxt.constSyms, s)
   205  	})
   206  }
   207  
   208  // GCLocalsSym generates a content-addressable sym containing data.
   209  func (ctxt *Link) GCLocalsSym(data []byte) *LSym {
   210  	sum := notsha256.Sum256(data)
   211  	str := base64.StdEncoding.EncodeToString(sum[:16])
   212  	return ctxt.LookupInit(fmt.Sprintf("gclocals·%s", str), func(lsym *LSym) {
   213  		lsym.P = data
   214  		lsym.Set(AttrContentAddressable, true)
   215  	})
   216  }
   217  
   218  // Assign index to symbols.
   219  // asm is set to true if this is called by the assembler (i.e. not the compiler),
   220  // in which case all the symbols are non-package (for now).
   221  func (ctxt *Link) NumberSyms() {
   222  	if ctxt.Pkgpath == "" {
   223  		panic("NumberSyms called without package path")
   224  	}
   225  
   226  	if ctxt.Headtype == objabi.Haix {
   227  		// Data must be in a reliable order for reproducible builds.
   228  		// The original entries are in a reliable order, but the TOC symbols
   229  		// that are added in Progedit are added by different goroutines
   230  		// that can be scheduled independently. We need to reorder those
   231  		// symbols reliably. Sort by name but use a stable sort, so that
   232  		// any original entries with the same name (all DWARFVAR symbols
   233  		// have empty names but different relocation sets) are not shuffled.
   234  		// TODO: Find a better place and optimize to only sort TOC symbols.
   235  		sort.SliceStable(ctxt.Data, func(i, j int) bool {
   236  			return ctxt.Data[i].Name < ctxt.Data[j].Name
   237  		})
   238  	}
   239  
   240  	// Constant symbols are created late in the concurrent phase. Sort them
   241  	// to ensure a deterministic order.
   242  	sort.Slice(ctxt.constSyms, func(i, j int) bool {
   243  		return ctxt.constSyms[i].Name < ctxt.constSyms[j].Name
   244  	})
   245  	ctxt.Data = append(ctxt.Data, ctxt.constSyms...)
   246  	ctxt.constSyms = nil
   247  
   248  	ctxt.pkgIdx = make(map[string]int32)
   249  	ctxt.defs = []*LSym{}
   250  	ctxt.hashed64defs = []*LSym{}
   251  	ctxt.hasheddefs = []*LSym{}
   252  	ctxt.nonpkgdefs = []*LSym{}
   253  
   254  	var idx, hashedidx, hashed64idx, nonpkgidx int32
   255  	ctxt.traverseSyms(traverseDefs|traversePcdata, func(s *LSym) {
   256  		if s.ContentAddressable() {
   257  			if s.Size <= 8 && len(s.R) == 0 && contentHashSection(s) == 0 {
   258  				// We can use short hash only for symbols without relocations.
   259  				// Don't use short hash for symbols that belong in a particular section
   260  				// or require special handling (such as type symbols).
   261  				s.PkgIdx = goobj.PkgIdxHashed64
   262  				s.SymIdx = hashed64idx
   263  				if hashed64idx != int32(len(ctxt.hashed64defs)) {
   264  					panic("bad index")
   265  				}
   266  				ctxt.hashed64defs = append(ctxt.hashed64defs, s)
   267  				hashed64idx++
   268  			} else {
   269  				s.PkgIdx = goobj.PkgIdxHashed
   270  				s.SymIdx = hashedidx
   271  				if hashedidx != int32(len(ctxt.hasheddefs)) {
   272  					panic("bad index")
   273  				}
   274  				ctxt.hasheddefs = append(ctxt.hasheddefs, s)
   275  				hashedidx++
   276  			}
   277  		} else if isNonPkgSym(ctxt, s) {
   278  			s.PkgIdx = goobj.PkgIdxNone
   279  			s.SymIdx = nonpkgidx
   280  			if nonpkgidx != int32(len(ctxt.nonpkgdefs)) {
   281  				panic("bad index")
   282  			}
   283  			ctxt.nonpkgdefs = append(ctxt.nonpkgdefs, s)
   284  			nonpkgidx++
   285  		} else {
   286  			s.PkgIdx = goobj.PkgIdxSelf
   287  			s.SymIdx = idx
   288  			if idx != int32(len(ctxt.defs)) {
   289  				panic("bad index")
   290  			}
   291  			ctxt.defs = append(ctxt.defs, s)
   292  			idx++
   293  		}
   294  		s.Set(AttrIndexed, true)
   295  	})
   296  
   297  	ipkg := int32(1) // 0 is invalid index
   298  	nonpkgdef := nonpkgidx
   299  	ctxt.traverseSyms(traverseRefs|traverseAux, func(rs *LSym) {
   300  		if rs.PkgIdx != goobj.PkgIdxInvalid {
   301  			return
   302  		}
   303  		if !ctxt.Flag_linkshared {
   304  			// Assign special index for builtin symbols.
   305  			// Don't do it when linking against shared libraries, as the runtime
   306  			// may be in a different library.
   307  			if i := goobj.BuiltinIdx(rs.Name, int(rs.ABI())); i != -1 {
   308  				rs.PkgIdx = goobj.PkgIdxBuiltin
   309  				rs.SymIdx = int32(i)
   310  				rs.Set(AttrIndexed, true)
   311  				return
   312  			}
   313  		}
   314  		pkg := rs.Pkg
   315  		if rs.ContentAddressable() {
   316  			// for now, only support content-addressable symbols that are always locally defined.
   317  			panic("hashed refs unsupported for now")
   318  		}
   319  		if pkg == "" || pkg == "\"\"" || pkg == "_" || !rs.Indexed() {
   320  			rs.PkgIdx = goobj.PkgIdxNone
   321  			rs.SymIdx = nonpkgidx
   322  			rs.Set(AttrIndexed, true)
   323  			if nonpkgidx != nonpkgdef+int32(len(ctxt.nonpkgrefs)) {
   324  				panic("bad index")
   325  			}
   326  			ctxt.nonpkgrefs = append(ctxt.nonpkgrefs, rs)
   327  			nonpkgidx++
   328  			return
   329  		}
   330  		if k, ok := ctxt.pkgIdx[pkg]; ok {
   331  			rs.PkgIdx = k
   332  			return
   333  		}
   334  		rs.PkgIdx = ipkg
   335  		ctxt.pkgIdx[pkg] = ipkg
   336  		ipkg++
   337  	})
   338  }
   339  
   340  // Returns whether s is a non-package symbol, which needs to be referenced
   341  // by name instead of by index.
   342  func isNonPkgSym(ctxt *Link, s *LSym) bool {
   343  	if ctxt.IsAsm && !s.Static() {
   344  		// asm symbols are referenced by name only, except static symbols
   345  		// which are file-local and can be referenced by index.
   346  		return true
   347  	}
   348  	if ctxt.Flag_linkshared {
   349  		// The referenced symbol may be in a different shared library so
   350  		// the linker cannot see its index.
   351  		return true
   352  	}
   353  	if s.Pkg == "_" {
   354  		// The frontend uses package "_" to mark symbols that should not
   355  		// be referenced by index, e.g. linkname'd symbols.
   356  		return true
   357  	}
   358  	if s.DuplicateOK() {
   359  		// Dupok symbol needs to be dedup'd by name.
   360  		return true
   361  	}
   362  	return false
   363  }
   364  
   365  // StaticNamePref is the prefix the front end applies to static temporary
   366  // variables. When turned into LSyms, these can be tagged as static so
   367  // as to avoid inserting them into the linker's name lookup tables.
   368  const StaticNamePref = ".stmp_"
   369  
   370  type traverseFlag uint32
   371  
   372  const (
   373  	traverseDefs traverseFlag = 1 << iota
   374  	traverseRefs
   375  	traverseAux
   376  	traversePcdata
   377  
   378  	traverseAll = traverseDefs | traverseRefs | traverseAux | traversePcdata
   379  )
   380  
   381  // Traverse symbols based on flag, call fn for each symbol.
   382  func (ctxt *Link) traverseSyms(flag traverseFlag, fn func(*LSym)) {
   383  	fnNoNil := func(s *LSym) {
   384  		if s != nil {
   385  			fn(s)
   386  		}
   387  	}
   388  	lists := [][]*LSym{ctxt.Text, ctxt.Data}
   389  	files := ctxt.PosTable.FileTable()
   390  	for _, list := range lists {
   391  		for _, s := range list {
   392  			if flag&traverseDefs != 0 {
   393  				fn(s)
   394  			}
   395  			if flag&traverseRefs != 0 {
   396  				for _, r := range s.R {
   397  					fnNoNil(r.Sym)
   398  				}
   399  			}
   400  			if flag&traverseAux != 0 {
   401  				fnNoNil(s.Gotype)
   402  				if s.Type == objabi.STEXT {
   403  					f := func(parent *LSym, aux *LSym) {
   404  						fn(aux)
   405  					}
   406  					ctxt.traverseFuncAux(flag, s, f, files)
   407  				} else if v := s.VarInfo(); v != nil {
   408  					fnNoNil(v.dwarfInfoSym)
   409  				}
   410  			}
   411  			if flag&traversePcdata != 0 && s.Type == objabi.STEXT {
   412  				fi := s.Func().Pcln
   413  				fnNoNil(fi.Pcsp)
   414  				fnNoNil(fi.Pcfile)
   415  				fnNoNil(fi.Pcline)
   416  				fnNoNil(fi.Pcinline)
   417  				for _, d := range fi.Pcdata {
   418  					fnNoNil(d)
   419  				}
   420  			}
   421  		}
   422  	}
   423  }
   424  
   425  func (ctxt *Link) traverseFuncAux(flag traverseFlag, fsym *LSym, fn func(parent *LSym, aux *LSym), files []string) {
   426  	fninfo := fsym.Func()
   427  	pc := &fninfo.Pcln
   428  	if flag&traverseAux == 0 {
   429  		// NB: should it become necessary to walk aux sym reloc references
   430  		// without walking the aux syms themselves, this can be changed.
   431  		panic("should not be here")
   432  	}
   433  	for _, d := range pc.Funcdata {
   434  		if d != nil {
   435  			fn(fsym, d)
   436  		}
   437  	}
   438  	usedFiles := make([]goobj.CUFileIndex, 0, len(pc.UsedFiles))
   439  	for f := range pc.UsedFiles {
   440  		usedFiles = append(usedFiles, f)
   441  	}
   442  	sort.Slice(usedFiles, func(i, j int) bool { return usedFiles[i] < usedFiles[j] })
   443  	for _, f := range usedFiles {
   444  		if filesym := ctxt.Lookup(files[f]); filesym != nil {
   445  			fn(fsym, filesym)
   446  		}
   447  	}
   448  	for _, call := range pc.InlTree.nodes {
   449  		if call.Func != nil {
   450  			fn(fsym, call.Func)
   451  		}
   452  	}
   453  
   454  	auxsyms := []*LSym{fninfo.dwarfRangesSym, fninfo.dwarfLocSym, fninfo.dwarfDebugLinesSym, fninfo.dwarfInfoSym, fninfo.WasmImportSym, fninfo.sehUnwindInfoSym}
   455  	for _, s := range auxsyms {
   456  		if s == nil || s.Size == 0 {
   457  			continue
   458  		}
   459  		fn(fsym, s)
   460  		if flag&traverseRefs != 0 {
   461  			for _, r := range s.R {
   462  				if r.Sym != nil {
   463  					fn(s, r.Sym)
   464  				}
   465  			}
   466  		}
   467  	}
   468  }
   469  
   470  // Traverse aux symbols, calling fn for each sym/aux pair.
   471  func (ctxt *Link) traverseAuxSyms(flag traverseFlag, fn func(parent *LSym, aux *LSym)) {
   472  	lists := [][]*LSym{ctxt.Text, ctxt.Data}
   473  	files := ctxt.PosTable.FileTable()
   474  	for _, list := range lists {
   475  		for _, s := range list {
   476  			if s.Gotype != nil {
   477  				if flag&traverseDefs != 0 {
   478  					fn(s, s.Gotype)
   479  				}
   480  			}
   481  			if s.Type == objabi.STEXT {
   482  				ctxt.traverseFuncAux(flag, s, fn, files)
   483  			} else if v := s.VarInfo(); v != nil && v.dwarfInfoSym != nil {
   484  				fn(s, v.dwarfInfoSym)
   485  			}
   486  		}
   487  	}
   488  }
   489
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