symbolbuilder.go

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