1 files changed, 440 insertions, 0 deletions
diff --git a/src/cmd/link/internal/loader/symbolbuilder.go b/src/cmd/link/internal/loader/symbolbuilder.go
new file mode 100644
index 0000000..5d37da8
--- /dev/null
+++ b/src/cmd/link/internal/loader/symbolbuilder.go
@@ -0,0 +1,440 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package loader
+
+import (
+	"cmd/internal/goobj"
+	"cmd/internal/objabi"
+	"cmd/internal/sys"
+	"cmd/link/internal/sym"
+	"sort"
+)
+
+// SymbolBuilder is a helper designed to help with the construction
+// of new symbol contents.
+type SymbolBuilder struct {
+	*extSymPayload         // points to payload being updated
+	symIdx         Sym     // index of symbol being updated/constructed
+	l              *Loader // loader
+}
+
+// MakeSymbolBuilder creates a symbol builder for use in constructing
+// an entirely new symbol.
+func (l *Loader) MakeSymbolBuilder(name string) *SymbolBuilder {
+	// for now assume that any new sym is intended to be static
+	symIdx := l.CreateStaticSym(name)
+	sb := &SymbolBuilder{l: l, symIdx: symIdx}
+	sb.extSymPayload = l.getPayload(symIdx)
+	return sb
+}
+
+// MakeSymbolUpdater creates a symbol builder helper for an existing
+// symbol 'symIdx'. If 'symIdx' is not an external symbol, then create
+// a clone of it (copy name, properties, etc) fix things up so that
+// the lookup tables and caches point to the new version, not the old
+// version.
+func (l *Loader) MakeSymbolUpdater(symIdx Sym) *SymbolBuilder {
+	if symIdx == 0 {
+		panic("can't update the null symbol")
+	}
+	if !l.IsExternal(symIdx) {
+		// Create a clone with the same name/version/kind etc.
+		l.cloneToExternal(symIdx)
+	}
+
+	// Construct updater and return.
+	sb := &SymbolBuilder{l: l, symIdx: symIdx}
+	sb.extSymPayload = l.getPayload(symIdx)
+	return sb
+}
+
+// CreateSymForUpdate creates a symbol with given name and version,
+// returns a CreateSymForUpdate for update. If the symbol already
+// exists, it will update in-place.
+func (l *Loader) CreateSymForUpdate(name string, version int) *SymbolBuilder {
+	s := l.LookupOrCreateSym(name, version)
+	l.SetAttrReachable(s, true)
+	return l.MakeSymbolUpdater(s)
+}
+
+// Getters for properties of the symbol we're working on.
+
+func (sb *SymbolBuilder) Sym() Sym               { return sb.symIdx }
+func (sb *SymbolBuilder) Name() string           { return sb.name }
+func (sb *SymbolBuilder) Version() int           { return sb.ver }
+func (sb *SymbolBuilder) Type() sym.SymKind      { return sb.kind }
+func (sb *SymbolBuilder) Size() int64            { return sb.size }
+func (sb *SymbolBuilder) Data() []byte           { return sb.data }
+func (sb *SymbolBuilder) Value() int64           { return sb.l.SymValue(sb.symIdx) }
+func (sb *SymbolBuilder) Align() int32           { return sb.l.SymAlign(sb.symIdx) }
+func (sb *SymbolBuilder) Localentry() uint8      { return sb.l.SymLocalentry(sb.symIdx) }
+func (sb *SymbolBuilder) OnList() bool           { return sb.l.AttrOnList(sb.symIdx) }
+func (sb *SymbolBuilder) External() bool         { return sb.l.AttrExternal(sb.symIdx) }
+func (sb *SymbolBuilder) Extname() string        { return sb.l.SymExtname(sb.symIdx) }
+func (sb *SymbolBuilder) CgoExportDynamic() bool { return sb.l.AttrCgoExportDynamic(sb.symIdx) }
+func (sb *SymbolBuilder) Dynimplib() string      { return sb.l.SymDynimplib(sb.symIdx) }
+func (sb *SymbolBuilder) Dynimpvers() string     { return sb.l.SymDynimpvers(sb.symIdx) }
+func (sb *SymbolBuilder) SubSym() Sym            { return sb.l.SubSym(sb.symIdx) }
+func (sb *SymbolBuilder) GoType() Sym            { return sb.l.SymGoType(sb.symIdx) }
+func (sb *SymbolBuilder) VisibilityHidden() bool { return sb.l.AttrVisibilityHidden(sb.symIdx) }
+func (sb *SymbolBuilder) Sect() *sym.Section     { return sb.l.SymSect(sb.symIdx) }
+
+// Setters for symbol properties.
+
+func (sb *SymbolBuilder) SetType(kind sym.SymKind)   { sb.kind = kind }
+func (sb *SymbolBuilder) SetSize(size int64)         { sb.size = size }
+func (sb *SymbolBuilder) SetData(data []byte)        { sb.data = data }
+func (sb *SymbolBuilder) SetOnList(v bool)           { sb.l.SetAttrOnList(sb.symIdx, v) }
+func (sb *SymbolBuilder) SetExternal(v bool)         { sb.l.SetAttrExternal(sb.symIdx, v) }
+func (sb *SymbolBuilder) SetValue(v int64)           { sb.l.SetSymValue(sb.symIdx, v) }
+func (sb *SymbolBuilder) SetAlign(align int32)       { sb.l.SetSymAlign(sb.symIdx, align) }
+func (sb *SymbolBuilder) SetLocalentry(value uint8)  { sb.l.SetSymLocalentry(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetExtname(value string)    { sb.l.SetSymExtname(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetDynimplib(value string)  { sb.l.SetSymDynimplib(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetDynimpvers(value string) { sb.l.SetSymDynimpvers(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetPlt(value int32)         { sb.l.SetPlt(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetGot(value int32)         { sb.l.SetGot(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetSpecial(value bool)      { sb.l.SetAttrSpecial(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetLocal(value bool)        { sb.l.SetAttrLocal(sb.symIdx, value) }
+func (sb *SymbolBuilder) SetVisibilityHidden(value bool) {
+	sb.l.SetAttrVisibilityHidden(sb.symIdx, value)
+}
+func (sb *SymbolBuilder) SetNotInSymbolTable(value bool) {
+	sb.l.SetAttrNotInSymbolTable(sb.symIdx, value)
+}
+func (sb *SymbolBuilder) SetSect(sect *sym.Section) { sb.l.SetSymSect(sb.symIdx, sect) }
+
+func (sb *SymbolBuilder) AddBytes(data []byte) {
+	if sb.kind == 0 {
+		sb.kind = sym.SDATA
+	}
+	sb.data = append(sb.data, data...)
+	sb.size = int64(len(sb.data))
+}
+
+func (sb *SymbolBuilder) Relocs() Relocs {
+	return sb.l.Relocs(sb.symIdx)
+}
+
+// ResetRelocs removes all relocations on this symbol.
+func (sb *SymbolBuilder) ResetRelocs() {
+	sb.relocs = sb.relocs[:0]
+	sb.reltypes = sb.reltypes[:0]
+}
+
+// SetRelocType sets the type of the 'i'-th relocation on this sym to 't'
+func (sb *SymbolBuilder) SetRelocType(i int, t objabi.RelocType) {
+	sb.relocs[i].SetType(0)
+	sb.reltypes[i] = t
+}
+
+// SetRelocSym sets the target sym of the 'i'-th relocation on this sym to 's'
+func (sb *SymbolBuilder) SetRelocSym(i int, tgt Sym) {
+	sb.relocs[i].SetSym(goobj.SymRef{PkgIdx: 0, SymIdx: uint32(tgt)})
+}
+
+// SetRelocAdd sets the addend of the 'i'-th relocation on this sym to 'a'
+func (sb *SymbolBuilder) SetRelocAdd(i int, a int64) {
+	sb.relocs[i].SetAdd(a)
+}
+
+// Add n relocations, return a handle to the relocations.
+func (sb *SymbolBuilder) AddRelocs(n int) Relocs {
+	sb.relocs = append(sb.relocs, make([]goobj.Reloc, n)...)
+	sb.reltypes = append(sb.reltypes, make([]objabi.RelocType, n)...)
+	return sb.l.Relocs(sb.symIdx)
+}
+
+// Add a relocation with given type, return its handle and index
+// (to set other fields).
+func (sb *SymbolBuilder) AddRel(typ objabi.RelocType) (Reloc, int) {
+	j := len(sb.relocs)
+	sb.relocs = append(sb.relocs, goobj.Reloc{})
+	sb.reltypes = append(sb.reltypes, typ)
+	relocs := sb.Relocs()
+	return relocs.At(j), j
+}
+
+// Sort relocations by offset.
+func (sb *SymbolBuilder) SortRelocs() {
+	sort.Sort((*relocsByOff)(sb.extSymPayload))
+}
+
+// Implement sort.Interface
+type relocsByOff extSymPayload
+
+func (p *relocsByOff) Len() int           { return len(p.relocs) }
+func (p *relocsByOff) Less(i, j int) bool { return p.relocs[i].Off() < p.relocs[j].Off() }
+func (p *relocsByOff) Swap(i, j int) {
+	p.relocs[i], p.relocs[j] = p.relocs[j], p.relocs[i]
+	p.reltypes[i], p.reltypes[j] = p.reltypes[j], p.reltypes[i]
+}
+
+func (sb *SymbolBuilder) Reachable() bool {
+	return sb.l.AttrReachable(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) SetReachable(v bool) {
+	sb.l.SetAttrReachable(sb.symIdx, v)
+}
+
+func (sb *SymbolBuilder) setReachable() {
+	sb.SetReachable(true)
+}
+
+func (sb *SymbolBuilder) ReadOnly() bool {
+	return sb.l.AttrReadOnly(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) SetReadOnly(v bool) {
+	sb.l.SetAttrReadOnly(sb.symIdx, v)
+}
+
+func (sb *SymbolBuilder) DuplicateOK() bool {
+	return sb.l.AttrDuplicateOK(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) SetDuplicateOK(v bool) {
+	sb.l.SetAttrDuplicateOK(sb.symIdx, v)
+}
+
+func (sb *SymbolBuilder) Outer() Sym {
+	return sb.l.OuterSym(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) Sub() Sym {
+	return sb.l.SubSym(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) SortSub() {
+	sb.l.SortSub(sb.symIdx)
+}
+
+func (sb *SymbolBuilder) AddInteriorSym(sub Sym) {
+	sb.l.AddInteriorSym(sb.symIdx, sub)
+}
+
+func (sb *SymbolBuilder) AddUint8(v uint8) int64 {
+	off := sb.size
+	if sb.kind == 0 {
+		sb.kind = sym.SDATA
+	}
+	sb.size++
+	sb.data = append(sb.data, v)
+	return off
+}
+
+func (sb *SymbolBuilder) AddUintXX(arch *sys.Arch, v uint64, wid int) int64 {
+	off := sb.size
+	sb.setUintXX(arch, off, v, int64(wid))
+	return off
+}
+
+func (sb *SymbolBuilder) setUintXX(arch *sys.Arch, off int64, v uint64, wid int64) int64 {
+	if sb.kind == 0 {
+		sb.kind = sym.SDATA
+	}
+	if sb.size < off+wid {
+		sb.size = off + wid
+		sb.Grow(sb.size)
+	}
+
+	switch wid {
+	case 1:
+		sb.data[off] = uint8(v)
+	case 2:
+		arch.ByteOrder.PutUint16(sb.data[off:], uint16(v))
+	case 4:
+		arch.ByteOrder.PutUint32(sb.data[off:], uint32(v))
+	case 8:
+		arch.ByteOrder.PutUint64(sb.data[off:], v)
+	}
+
+	return off + wid
+}
+
+func (sb *SymbolBuilder) AddUint16(arch *sys.Arch, v uint16) int64 {
+	return sb.AddUintXX(arch, uint64(v), 2)
+}
+
+func (sb *SymbolBuilder) AddUint32(arch *sys.Arch, v uint32) int64 {
+	return sb.AddUintXX(arch, uint64(v), 4)
+}
+
+func (sb *SymbolBuilder) AddUint64(arch *sys.Arch, v uint64) int64 {
+	return sb.AddUintXX(arch, v, 8)
+}
+
+func (sb *SymbolBuilder) AddUint(arch *sys.Arch, v uint64) int64 {
+	return sb.AddUintXX(arch, v, arch.PtrSize)
+}
+
+func (sb *SymbolBuilder) SetUint8(arch *sys.Arch, r int64, v uint8) int64 {
+	return sb.setUintXX(arch, r, uint64(v), 1)
+}
+
+func (sb *SymbolBuilder) SetUint16(arch *sys.Arch, r int64, v uint16) int64 {
+	return sb.setUintXX(arch, r, uint64(v), 2)
+}
+
+func (sb *SymbolBuilder) SetUint32(arch *sys.Arch, r int64, v uint32) int64 {
+	return sb.setUintXX(arch, r, uint64(v), 4)
+}
+
+func (sb *SymbolBuilder) SetUint(arch *sys.Arch, r int64, v uint64) int64 {
+	return sb.setUintXX(arch, r, v, int64(arch.PtrSize))
+}
+
+func (sb *SymbolBuilder) SetUintptr(arch *sys.Arch, r int64, v uintptr) int64 {
+	return sb.setUintXX(arch, r, uint64(v), int64(arch.PtrSize))
+}
+
+func (sb *SymbolBuilder) SetAddrPlus(arch *sys.Arch, off int64, tgt Sym, add int64) int64 {
+	if sb.Type() == 0 {
+		sb.SetType(sym.SDATA)
+	}
+	if off+int64(arch.PtrSize) > sb.size {
+		sb.size = off + int64(arch.PtrSize)
+		sb.Grow(sb.size)
+	}
+	r, _ := sb.AddRel(objabi.R_ADDR)
+	r.SetSym(tgt)
+	r.SetOff(int32(off))
+	r.SetSiz(uint8(arch.PtrSize))
+	r.SetAdd(add)
+	return off + int64(r.Siz())
+}
+
+func (sb *SymbolBuilder) SetAddr(arch *sys.Arch, off int64, tgt Sym) int64 {
+	return sb.SetAddrPlus(arch, off, tgt, 0)
+}
+
+func (sb *SymbolBuilder) AddStringAt(off int64, str string) int64 {
+	strLen := int64(len(str))
+	if off+strLen+1 > int64(len(sb.data)) {
+		panic("attempt to write past end of buffer")
+	}
+	copy(sb.data[off:off+strLen], str)
+	sb.data[off+strLen] = 0
+	return off + strLen + 1
+}
+
+func (sb *SymbolBuilder) Addstring(str string) int64 {
+	if sb.kind == 0 {
+		sb.kind = sym.SNOPTRDATA
+	}
+	r := sb.size
+	if sb.name == ".shstrtab" {
+		// FIXME: find a better mechanism for this
+		sb.l.elfsetstring(str, int(r))
+	}
+	sb.data = append(sb.data, str...)
+	sb.data = append(sb.data, 0)
+	sb.size = int64(len(sb.data))
+	return r
+}
+
+func (sb *SymbolBuilder) SetBytesAt(off int64, b []byte) int64 {
+	datLen := int64(len(b))
+	if off+datLen > int64(len(sb.data)) {
+		panic("attempt to write past end of buffer")
+	}
+	copy(sb.data[off:off+datLen], b)
+	return off + datLen
+}
+
+func (sb *SymbolBuilder) addSymRef(tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
+	if sb.kind == 0 {
+		sb.kind = sym.SDATA
+	}
+	i := sb.size
+
+	sb.size += int64(rsize)
+	sb.Grow(sb.size)
+
+	r, _ := sb.AddRel(typ)
+	r.SetSym(tgt)
+	r.SetOff(int32(i))
+	r.SetSiz(uint8(rsize))
+	r.SetAdd(add)
+
+	return i + int64(rsize)
+}
+
+// Add a symbol reference (relocation) with given type, addend, and size
+// (the most generic form).
+func (sb *SymbolBuilder) AddSymRef(arch *sys.Arch, tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
+	return sb.addSymRef(tgt, add, typ, rsize)
+}
+
+func (sb *SymbolBuilder) AddAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
+	return sb.addSymRef(tgt, add, objabi.R_ADDR, arch.PtrSize)
+}
+
+func (sb *SymbolBuilder) AddAddrPlus4(arch *sys.Arch, tgt Sym, add int64) int64 {
+	return sb.addSymRef(tgt, add, objabi.R_ADDR, 4)
+}
+
+func (sb *SymbolBuilder) AddAddr(arch *sys.Arch, tgt Sym) int64 {
+	return sb.AddAddrPlus(arch, tgt, 0)
+}
+
+func (sb *SymbolBuilder) AddPCRelPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
+	return sb.addSymRef(tgt, add, objabi.R_PCREL, 4)
+}
+
+func (sb *SymbolBuilder) AddCURelativeAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
+	return sb.addSymRef(tgt, add, objabi.R_ADDRCUOFF, arch.PtrSize)
+}
+
+func (sb *SymbolBuilder) AddSize(arch *sys.Arch, tgt Sym) int64 {
+	return sb.addSymRef(tgt, 0, objabi.R_SIZE, arch.PtrSize)
+}
+
+// GenAddAddrPlusFunc returns a function to be called when capturing
+// a function symbol's address. In later stages of the link (when
+// address assignment is done) when doing internal linking and
+// targeting an executable, we can just emit the address of a function
+// directly instead of generating a relocation. Clients can call
+// this function (setting 'internalExec' based on build mode and target)
+// and then invoke the returned function in roughly the same way that
+// loader.*SymbolBuilder.AddAddrPlus would be used.
+func GenAddAddrPlusFunc(internalExec bool) func(s *SymbolBuilder, arch *sys.Arch, tgt Sym, add int64) int64 {
+	if internalExec {
+		return func(s *SymbolBuilder, arch *sys.Arch, tgt Sym, add int64) int64 {
+			if v := s.l.SymValue(tgt); v != 0 {
+				return s.AddUint(arch, uint64(v+add))
+			}
+			return s.AddAddrPlus(arch, tgt, add)
+		}
+	} else {
+		return (*SymbolBuilder).AddAddrPlus
+	}
+}
+
+func (sb *SymbolBuilder) MakeWritable() {
+	if sb.ReadOnly() {
+		sb.data = append([]byte(nil), sb.data...)
+		sb.l.SetAttrReadOnly(sb.symIdx, false)
+	}
+}
+
+func (sb *SymbolBuilder) AddUleb(v uint64) {
+	if v < 128 { // common case: 1 byte
+		sb.AddUint8(uint8(v))
+		return
+	}
+	for {
+		c := uint8(v & 0x7f)
+		v >>= 7
+		if v != 0 {
+			c |= 0x80
+		}
+		sb.AddUint8(c)
+		if c&0x80 == 0 {
+			break
+		}
+	}
+}