symbolbuilder.go

Documentation: cmd/link/internal/loader

     1  // Copyright 2019 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 loader
     6  
     7  import (
     8  	"cmd/internal/goobj"
     9  	"cmd/internal/objabi"
    10  	"cmd/internal/sys"
    11  	"cmd/link/internal/sym"
    12  	"sort"
    13  )
    14  
    15  // SymbolBuilder is a helper designed to help with the construction
    16  // of new symbol contents.
    17  type SymbolBuilder struct {
    18  	*extSymPayload         // points to payload being updated
    19  	symIdx         Sym     // index of symbol being updated/constructed
    20  	l              *Loader // loader
    21  }
    22  
    23  // MakeSymbolBuilder creates a symbol builder for use in constructing
    24  // an entirely new symbol.
    25  func (l *Loader) MakeSymbolBuilder(name string) *SymbolBuilder {
    26  	// for now assume that any new sym is intended to be static
    27  	symIdx := l.CreateStaticSym(name)
    28  	sb := &SymbolBuilder{l: l, symIdx: symIdx}
    29  	sb.extSymPayload = l.getPayload(symIdx)
    30  	return sb
    31  }
    32  
    33  // MakeSymbolUpdater creates a symbol builder helper for an existing
    34  // symbol 'symIdx'. If 'symIdx' is not an external symbol, then create
    35  // a clone of it (copy name, properties, etc) fix things up so that
    36  // the lookup tables and caches point to the new version, not the old
    37  // version.
    38  func (l *Loader) MakeSymbolUpdater(symIdx Sym) *SymbolBuilder {
    39  	if symIdx == 0 {
    40  		panic("can't update the null symbol")
    41  	}
    42  	if !l.IsExternal(symIdx) {
    43  		// Create a clone with the same name/version/kind etc.
    44  		l.cloneToExternal(symIdx)
    45  	}
    46  
    47  	// Construct updater and return.
    48  	sb := &SymbolBuilder{l: l, symIdx: symIdx}
    49  	sb.extSymPayload = l.getPayload(symIdx)
    50  	return sb
    51  }
    52  
    53  // CreateSymForUpdate creates a symbol with given name and version,
    54  // returns a CreateSymForUpdate for update. If the symbol already
    55  // exists, it will update in-place.
    56  func (l *Loader) CreateSymForUpdate(name string, version int) *SymbolBuilder {
    57  	s := l.LookupOrCreateSym(name, version)
    58  	l.SetAttrReachable(s, true)
    59  	return l.MakeSymbolUpdater(s)
    60  }
    61  
    62  // Getters for properties of the symbol we're working on.
    63  
    64  func (sb *SymbolBuilder) Sym() Sym               { return sb.symIdx }
    65  func (sb *SymbolBuilder) Name() string           { return sb.name }
    66  func (sb *SymbolBuilder) Version() int           { return sb.ver }
    67  func (sb *SymbolBuilder) Type() sym.SymKind      { return sb.kind }
    68  func (sb *SymbolBuilder) Size() int64            { return sb.size }
    69  func (sb *SymbolBuilder) Data() []byte           { return sb.data }
    70  func (sb *SymbolBuilder) Value() int64           { return sb.l.SymValue(sb.symIdx) }
    71  func (sb *SymbolBuilder) Align() int32           { return sb.l.SymAlign(sb.symIdx) }
    72  func (sb *SymbolBuilder) Localentry() uint8      { return sb.l.SymLocalentry(sb.symIdx) }
    73  func (sb *SymbolBuilder) OnList() bool           { return sb.l.AttrOnList(sb.symIdx) }
    74  func (sb *SymbolBuilder) External() bool         { return sb.l.AttrExternal(sb.symIdx) }
    75  func (sb *SymbolBuilder) Extname() string        { return sb.l.SymExtname(sb.symIdx) }
    76  func (sb *SymbolBuilder) CgoExportDynamic() bool { return sb.l.AttrCgoExportDynamic(sb.symIdx) }
    77  func (sb *SymbolBuilder) Dynimplib() string      { return sb.l.SymDynimplib(sb.symIdx) }
    78  func (sb *SymbolBuilder) Dynimpvers() string     { return sb.l.SymDynimpvers(sb.symIdx) }
    79  func (sb *SymbolBuilder) SubSym() Sym            { return sb.l.SubSym(sb.symIdx) }
    80  func (sb *SymbolBuilder) GoType() Sym            { return sb.l.SymGoType(sb.symIdx) }
    81  func (sb *SymbolBuilder) VisibilityHidden() bool { return sb.l.AttrVisibilityHidden(sb.symIdx) }
    82  func (sb *SymbolBuilder) Sect() *sym.Section     { return sb.l.SymSect(sb.symIdx) }
    83  
    84  // Setters for symbol properties.
    85  
    86  func (sb *SymbolBuilder) SetType(kind sym.SymKind)   { sb.kind = kind }
    87  func (sb *SymbolBuilder) SetSize(size int64)         { sb.size = size }
    88  func (sb *SymbolBuilder) SetData(data []byte)        { sb.data = data }
    89  func (sb *SymbolBuilder) SetOnList(v bool)           { sb.l.SetAttrOnList(sb.symIdx, v) }
    90  func (sb *SymbolBuilder) SetExternal(v bool)         { sb.l.SetAttrExternal(sb.symIdx, v) }
    91  func (sb *SymbolBuilder) SetValue(v int64)           { sb.l.SetSymValue(sb.symIdx, v) }
    92  func (sb *SymbolBuilder) SetAlign(align int32)       { sb.l.SetSymAlign(sb.symIdx, align) }
    93  func (sb *SymbolBuilder) SetLocalentry(value uint8)  { sb.l.SetSymLocalentry(sb.symIdx, value) }
    94  func (sb *SymbolBuilder) SetExtname(value string)    { sb.l.SetSymExtname(sb.symIdx, value) }
    95  func (sb *SymbolBuilder) SetDynimplib(value string)  { sb.l.SetSymDynimplib(sb.symIdx, value) }
    96  func (sb *SymbolBuilder) SetDynimpvers(value string) { sb.l.SetSymDynimpvers(sb.symIdx, value) }
    97  func (sb *SymbolBuilder) SetPlt(value int32)         { sb.l.SetPlt(sb.symIdx, value) }
    98  func (sb *SymbolBuilder) SetGot(value int32)         { sb.l.SetGot(sb.symIdx, value) }
    99  func (sb *SymbolBuilder) SetSpecial(value bool)      { sb.l.SetAttrSpecial(sb.symIdx, value) }
   100  func (sb *SymbolBuilder) SetLocal(value bool)        { sb.l.SetAttrLocal(sb.symIdx, value) }
   101  func (sb *SymbolBuilder) SetVisibilityHidden(value bool) {
   102  	sb.l.SetAttrVisibilityHidden(sb.symIdx, value)
   103  }
   104  func (sb *SymbolBuilder) SetNotInSymbolTable(value bool) {
   105  	sb.l.SetAttrNotInSymbolTable(sb.symIdx, value)
   106  }
   107  func (sb *SymbolBuilder) SetSect(sect *sym.Section) { sb.l.SetSymSect(sb.symIdx, sect) }
   108  
   109  func (sb *SymbolBuilder) AddBytes(data []byte) {
   110  	if sb.kind == 0 {
   111  		sb.kind = sym.SDATA
   112  	}
   113  	sb.data = append(sb.data, data...)
   114  	sb.size = int64(len(sb.data))
   115  }
   116  
   117  func (sb *SymbolBuilder) Relocs() Relocs {
   118  	return sb.l.Relocs(sb.symIdx)
   119  }
   120  
   121  // ResetRelocs removes all relocations on this symbol.
   122  func (sb *SymbolBuilder) ResetRelocs() {
   123  	sb.relocs = sb.relocs[:0]
   124  }
   125  
   126  // SetRelocType sets the type of the 'i'-th relocation on this sym to 't'
   127  func (sb *SymbolBuilder) SetRelocType(i int, t objabi.RelocType) {
   128  	sb.relocs[i].SetType(uint16(t))
   129  }
   130  
   131  // SetRelocSym sets the target sym of the 'i'-th relocation on this sym to 's'
   132  func (sb *SymbolBuilder) SetRelocSym(i int, tgt Sym) {
   133  	sb.relocs[i].SetSym(goobj.SymRef{PkgIdx: 0, SymIdx: uint32(tgt)})
   134  }
   135  
   136  // SetRelocAdd sets the addend of the 'i'-th relocation on this sym to 'a'
   137  func (sb *SymbolBuilder) SetRelocAdd(i int, a int64) {
   138  	sb.relocs[i].SetAdd(a)
   139  }
   140  
   141  // Add n relocations, return a handle to the relocations.
   142  func (sb *SymbolBuilder) AddRelocs(n int) Relocs {
   143  	sb.relocs = append(sb.relocs, make([]goobj.Reloc, n)...)
   144  	return sb.l.Relocs(sb.symIdx)
   145  }
   146  
   147  // Add a relocation with given type, return its handle and index
   148  // (to set other fields).
   149  func (sb *SymbolBuilder) AddRel(typ objabi.RelocType) (Reloc, int) {
   150  	j := len(sb.relocs)
   151  	sb.relocs = append(sb.relocs, goobj.Reloc{})
   152  	sb.relocs[j].SetType(uint16(typ))
   153  	relocs := sb.Relocs()
   154  	return relocs.At(j), j
   155  }
   156  
   157  // Sort relocations by offset.
   158  func (sb *SymbolBuilder) SortRelocs() {
   159  	sort.Sort((*relocsByOff)(sb.extSymPayload))
   160  }
   161  
   162  // Implement sort.Interface
   163  type relocsByOff extSymPayload
   164  
   165  func (p *relocsByOff) Len() int           { return len(p.relocs) }
   166  func (p *relocsByOff) Less(i, j int) bool { return p.relocs[i].Off() < p.relocs[j].Off() }
   167  func (p *relocsByOff) Swap(i, j int) {
   168  	p.relocs[i], p.relocs[j] = p.relocs[j], p.relocs[i]
   169  }
   170  
   171  func (sb *SymbolBuilder) Reachable() bool {
   172  	return sb.l.AttrReachable(sb.symIdx)
   173  }
   174  
   175  func (sb *SymbolBuilder) SetReachable(v bool) {
   176  	sb.l.SetAttrReachable(sb.symIdx, v)
   177  }
   178  
   179  func (sb *SymbolBuilder) ReadOnly() bool {
   180  	return sb.l.AttrReadOnly(sb.symIdx)
   181  }
   182  
   183  func (sb *SymbolBuilder) SetReadOnly(v bool) {
   184  	sb.l.SetAttrReadOnly(sb.symIdx, v)
   185  }
   186  
   187  func (sb *SymbolBuilder) DuplicateOK() bool {
   188  	return sb.l.AttrDuplicateOK(sb.symIdx)
   189  }
   190  
   191  func (sb *SymbolBuilder) SetDuplicateOK(v bool) {
   192  	sb.l.SetAttrDuplicateOK(sb.symIdx, v)
   193  }
   194  
   195  func (sb *SymbolBuilder) Outer() Sym {
   196  	return sb.l.OuterSym(sb.symIdx)
   197  }
   198  
   199  func (sb *SymbolBuilder) Sub() Sym {
   200  	return sb.l.SubSym(sb.symIdx)
   201  }
   202  
   203  func (sb *SymbolBuilder) SortSub() {
   204  	sb.l.SortSub(sb.symIdx)
   205  }
   206  
   207  func (sb *SymbolBuilder) AddInteriorSym(sub Sym) {
   208  	sb.l.AddInteriorSym(sb.symIdx, sub)
   209  }
   210  
   211  func (sb *SymbolBuilder) AddUint8(v uint8) int64 {
   212  	off := sb.size
   213  	if sb.kind == 0 {
   214  		sb.kind = sym.SDATA
   215  	}
   216  	sb.size++
   217  	sb.data = append(sb.data, v)
   218  	return off
   219  }
   220  
   221  func (sb *SymbolBuilder) AddUintXX(arch *sys.Arch, v uint64, wid int) int64 {
   222  	off := sb.size
   223  	sb.setUintXX(arch, off, v, int64(wid))
   224  	return off
   225  }
   226  
   227  func (sb *SymbolBuilder) setUintXX(arch *sys.Arch, off int64, v uint64, wid int64) int64 {
   228  	if sb.kind == 0 {
   229  		sb.kind = sym.SDATA
   230  	}
   231  	if sb.size < off+wid {
   232  		sb.size = off + wid
   233  		sb.Grow(sb.size)
   234  	}
   235  
   236  	switch wid {
   237  	case 1:
   238  		sb.data[off] = uint8(v)
   239  	case 2:
   240  		arch.ByteOrder.PutUint16(sb.data[off:], uint16(v))
   241  	case 4:
   242  		arch.ByteOrder.PutUint32(sb.data[off:], uint32(v))
   243  	case 8:
   244  		arch.ByteOrder.PutUint64(sb.data[off:], v)
   245  	}
   246  
   247  	return off + wid
   248  }
   249  
   250  func (sb *SymbolBuilder) AddUint16(arch *sys.Arch, v uint16) int64 {
   251  	return sb.AddUintXX(arch, uint64(v), 2)
   252  }
   253  
   254  func (sb *SymbolBuilder) AddUint32(arch *sys.Arch, v uint32) int64 {
   255  	return sb.AddUintXX(arch, uint64(v), 4)
   256  }
   257  
   258  func (sb *SymbolBuilder) AddUint64(arch *sys.Arch, v uint64) int64 {
   259  	return sb.AddUintXX(arch, v, 8)
   260  }
   261  
   262  func (sb *SymbolBuilder) AddUint(arch *sys.Arch, v uint64) int64 {
   263  	return sb.AddUintXX(arch, v, arch.PtrSize)
   264  }
   265  
   266  func (sb *SymbolBuilder) SetUint8(arch *sys.Arch, r int64, v uint8) int64 {
   267  	return sb.setUintXX(arch, r, uint64(v), 1)
   268  }
   269  
   270  func (sb *SymbolBuilder) SetUint16(arch *sys.Arch, r int64, v uint16) int64 {
   271  	return sb.setUintXX(arch, r, uint64(v), 2)
   272  }
   273  
   274  func (sb *SymbolBuilder) SetUint32(arch *sys.Arch, r int64, v uint32) int64 {
   275  	return sb.setUintXX(arch, r, uint64(v), 4)
   276  }
   277  
   278  func (sb *SymbolBuilder) SetUint(arch *sys.Arch, r int64, v uint64) int64 {
   279  	return sb.setUintXX(arch, r, v, int64(arch.PtrSize))
   280  }
   281  
   282  func (sb *SymbolBuilder) SetUintptr(arch *sys.Arch, r int64, v uintptr) int64 {
   283  	return sb.setUintXX(arch, r, uint64(v), int64(arch.PtrSize))
   284  }
   285  
   286  func (sb *SymbolBuilder) SetAddrPlus(arch *sys.Arch, off int64, tgt Sym, add int64) int64 {
   287  	if sb.Type() == 0 {
   288  		sb.SetType(sym.SDATA)
   289  	}
   290  	if off+int64(arch.PtrSize) > sb.size {
   291  		sb.size = off + int64(arch.PtrSize)
   292  		sb.Grow(sb.size)
   293  	}
   294  	r, _ := sb.AddRel(objabi.R_ADDR)
   295  	r.SetSym(tgt)
   296  	r.SetOff(int32(off))
   297  	r.SetSiz(uint8(arch.PtrSize))
   298  	r.SetAdd(add)
   299  	return off + int64(r.Siz())
   300  }
   301  
   302  func (sb *SymbolBuilder) SetAddr(arch *sys.Arch, off int64, tgt Sym) int64 {
   303  	return sb.SetAddrPlus(arch, off, tgt, 0)
   304  }
   305  
   306  func (sb *SymbolBuilder) AddStringAt(off int64, str string) int64 {
   307  	strLen := int64(len(str))
   308  	if off+strLen > int64(len(sb.data)) {
   309  		panic("attempt to write past end of buffer")
   310  	}
   311  	copy(sb.data[off:off+strLen], str)
   312  	return off + strLen
   313  }
   314  
   315  // AddCStringAt adds str plus a null terminating byte.
   316  func (sb *SymbolBuilder) AddCStringAt(off int64, str string) int64 {
   317  	strLen := int64(len(str))
   318  	if off+strLen+1 > int64(len(sb.data)) {
   319  		panic("attempt to write past end of buffer")
   320  	}
   321  	copy(sb.data[off:off+strLen], str)
   322  	sb.data[off+strLen] = 0
   323  	return off + strLen + 1
   324  }
   325  
   326  func (sb *SymbolBuilder) Addstring(str string) int64 {
   327  	if sb.kind == 0 {
   328  		sb.kind = sym.SNOPTRDATA
   329  	}
   330  	r := sb.size
   331  	sb.data = append(sb.data, str...)
   332  	sb.data = append(sb.data, 0)
   333  	sb.size = int64(len(sb.data))
   334  	return r
   335  }
   336  
   337  func (sb *SymbolBuilder) SetBytesAt(off int64, b []byte) int64 {
   338  	datLen := int64(len(b))
   339  	if off+datLen > int64(len(sb.data)) {
   340  		panic("attempt to write past end of buffer")
   341  	}
   342  	copy(sb.data[off:off+datLen], b)
   343  	return off + datLen
   344  }
   345  
   346  func (sb *SymbolBuilder) addSymRef(tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
   347  	if sb.kind == 0 {
   348  		sb.kind = sym.SDATA
   349  	}
   350  	i := sb.size
   351  
   352  	sb.size += int64(rsize)
   353  	sb.Grow(sb.size)
   354  
   355  	r, _ := sb.AddRel(typ)
   356  	r.SetSym(tgt)
   357  	r.SetOff(int32(i))
   358  	r.SetSiz(uint8(rsize))
   359  	r.SetAdd(add)
   360  
   361  	return i + int64(rsize)
   362  }
   363  
   364  // Add a symbol reference (relocation) with given type, addend, and size
   365  // (the most generic form).
   366  func (sb *SymbolBuilder) AddSymRef(arch *sys.Arch, tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
   367  	return sb.addSymRef(tgt, add, typ, rsize)
   368  }
   369  
   370  func (sb *SymbolBuilder) AddAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
   371  	return sb.addSymRef(tgt, add, objabi.R_ADDR, arch.PtrSize)
   372  }
   373  
   374  func (sb *SymbolBuilder) AddAddrPlus4(arch *sys.Arch, tgt Sym, add int64) int64 {
   375  	return sb.addSymRef(tgt, add, objabi.R_ADDR, 4)
   376  }
   377  
   378  func (sb *SymbolBuilder) AddAddr(arch *sys.Arch, tgt Sym) int64 {
   379  	return sb.AddAddrPlus(arch, tgt, 0)
   380  }
   381  
   382  func (sb *SymbolBuilder) AddPEImageRelativeAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
   383  	return sb.addSymRef(tgt, add, objabi.R_PEIMAGEOFF, 4)
   384  }
   385  
   386  func (sb *SymbolBuilder) AddPCRelPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
   387  	return sb.addSymRef(tgt, add, objabi.R_PCREL, 4)
   388  }
   389  
   390  func (sb *SymbolBuilder) AddCURelativeAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
   391  	return sb.addSymRef(tgt, add, objabi.R_ADDRCUOFF, arch.PtrSize)
   392  }
   393  
   394  func (sb *SymbolBuilder) AddSize(arch *sys.Arch, tgt Sym) int64 {
   395  	return sb.addSymRef(tgt, 0, objabi.R_SIZE, arch.PtrSize)
   396  }
   397  
   398  // GenAddAddrPlusFunc returns a function to be called when capturing
   399  // a function symbol's address. In later stages of the link (when
   400  // address assignment is done) when doing internal linking and
   401  // targeting an executable, we can just emit the address of a function
   402  // directly instead of generating a relocation. Clients can call
   403  // this function (setting 'internalExec' based on build mode and target)
   404  // and then invoke the returned function in roughly the same way that
   405  // loader.*SymbolBuilder.AddAddrPlus would be used.
   406  func GenAddAddrPlusFunc(internalExec bool) func(s *SymbolBuilder, arch *sys.Arch, tgt Sym, add int64) int64 {
   407  	if internalExec {
   408  		return func(s *SymbolBuilder, arch *sys.Arch, tgt Sym, add int64) int64 {
   409  			if v := s.l.SymValue(tgt); v != 0 {
   410  				return s.AddUint(arch, uint64(v+add))
   411  			}
   412  			return s.AddAddrPlus(arch, tgt, add)
   413  		}
   414  	} else {
   415  		return (*SymbolBuilder).AddAddrPlus
   416  	}
   417  }
   418  
   419  func (sb *SymbolBuilder) MakeWritable() {
   420  	if sb.ReadOnly() {
   421  		sb.data = append([]byte(nil), sb.data...)
   422  		sb.l.SetAttrReadOnly(sb.symIdx, false)
   423  	}
   424  }
   425  
   426  func (sb *SymbolBuilder) AddUleb(v uint64) {
   427  	if v < 128 { // common case: 1 byte
   428  		sb.AddUint8(uint8(v))
   429  		return
   430  	}
   431  	for {
   432  		c := uint8(v & 0x7f)
   433  		v >>= 7
   434  		if v != 0 {
   435  			c |= 0x80
   436  		}
   437  		sb.AddUint8(c)
   438  		if c&0x80 == 0 {
   439  			break
   440  		}
   441  	}
   442  }
   443
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