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[dev.link] cmd/link: add SymbolBuilder helper

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Add SymbolBuilder helper type -- this type provides a set of methods
intended to make it easy to manipulate the content of a symbol (type,
relocations, data, etc).

Change-Id: I579bf8d04650e66d33a9780a6c2347a576c94c6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/210178
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2019-12-11 14:36:17 -05:00
parent c6fea80b95
commit b720014743
4 changed files with 491 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/cmd/link/internal/ld/lib.go
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@ -388,7 +388,7 @@ func (ctxt *Link) loadlib() {
default:
log.Fatalf("invalid -strictdups flag value %d", *FlagStrictDups)
}
ctxt.loader = loader.NewLoader(flags)
ctxt.loader = loader.NewLoader(flags, elfsetstring)
ctxt.cgo_export_static = make(map[string]bool)
ctxt.cgo_export_dynamic = make(map[string]bool)

22
src/cmd/link/internal/loader/loader.go
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@ -211,8 +211,12 @@ type Loader struct {
flags uint32
strictDupMsgs int // number of strict-dup warning/errors, when FlagStrictDups is enabled
elfsetstring elfsetstringFunc
}
type elfsetstringFunc func(s *sym.Symbol, str string, off int)
// extSymPayload holds the payload (data + relocations) for linker-synthesized
// external symbols (note that symbol value is stored in a separate slice).
type extSymPayload struct {
@ -229,7 +233,7 @@ const (
FlagStrictDups = 1 << iota
)
func NewLoader(flags uint32) *Loader {
func NewLoader(flags uint32, elfsetstring elfsetstringFunc) *Loader {
nbuiltin := goobj2.NBuiltin()
return &Loader{
start: make(map[*oReader]Sym),
@ -252,6 +256,7 @@ func NewLoader(flags uint32) *Loader {
extStaticSyms: make(map[nameVer]Sym),
builtinSyms: make([]Sym, nbuiltin),
flags: flags,
elfsetstring: elfsetstring,
}
}
@ -392,6 +397,21 @@ func (l *Loader) getPayload(i Sym) *extSymPayload {
return &l.payloads[pi]
}
func (ms *extSymPayload) Grow(siz int64) {
if int64(int(siz)) != siz {
log.Fatalf("symgrow size %d too long", siz)
}
if int64(len(ms.data)) >= siz {
return
}
if cap(ms.data) < int(siz) {
cl := len(ms.data)
ms.data = append(ms.data, make([]byte, int(siz)+1-cl)...)
ms.data = ms.data[0:cl]
}
ms.data = ms.data[:siz]
}
// Ensure Syms slice has enough space, as well as growing the
// 'payloads' slice.
func (l *Loader) growSyms(i int) {

223
src/cmd/link/internal/loader/loader_test.go
View File

@ -5,6 +5,9 @@
package loader
import (
"bytes"
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/sym"
"fmt"
"testing"
@ -26,14 +29,15 @@ func addDummyObjSym(t *testing.T, ldr *Loader, or *oReader, name string) Sym {
}
func TestAddMaterializedSymbol(t *testing.T) {
ldr := NewLoader(0)
edummy := func(s *sym.Symbol, str string, off int) {}
ldr := NewLoader(0, edummy)
dummyOreader := oReader{version: -1}
or := &dummyOreader
// Create some syms from a dummy object file symbol to get things going.
addDummyObjSym(t, ldr, or, "type.uint8")
ts1 := addDummyObjSym(t, ldr, or, "type.uint8")
ts2 := addDummyObjSym(t, ldr, or, "mumble")
addDummyObjSym(t, ldr, or, "type.string")
ts3 := addDummyObjSym(t, ldr, or, "type.string")
// Create some external symbols.
es1 := ldr.AddExtSym("extnew1", 0)
@ -54,6 +58,22 @@ func TestAddMaterializedSymbol(t *testing.T) {
t.Fatalf("CreateExtSym failed for nameless sym")
}
// Grab symbol builder pointers
sb1 := ldr.MakeSymbolUpdater(es1)
sb2 := ldr.MakeSymbolUpdater(es2)
sb3 := ldr.MakeSymbolUpdater(es3)
// Check get/set symbol type
es3typ := sb3.Type()
if es3typ != sym.Sxxx {
t.Errorf("SymType(es3): expected %d, got %d", sym.Sxxx, es3typ)
}
sb2.SetType(sym.SRODATA)
es3typ = sb2.Type()
if es3typ != sym.SRODATA {
t.Errorf("SymType(es3): expected %d, got %d", sym.SRODATA, es3typ)
}
// New symbols should not initially be reachable.
if ldr.AttrReachable(es1) || ldr.AttrReachable(es2) || ldr.AttrReachable(es3) {
t.Errorf("newly materialized symbols should not be reachable")
@ -88,6 +108,9 @@ func TestAddMaterializedSymbol(t *testing.T) {
}
}
sb1 = ldr.MakeSymbolUpdater(es1)
sb2 = ldr.MakeSymbolUpdater(es2)
// Get/set a few other attributes
if ldr.AttrVisibilityHidden(es3) {
t.Errorf("expected initially not hidden")
@ -120,10 +143,202 @@ func TestAddMaterializedSymbol(t *testing.T) {
if es3al != 128 {
t.Errorf("SymAlign(es3): expected 128, got %d", es3al)
}
// Add some relocations to the new symbols.
r1 := Reloc{0, 1, objabi.R_ADDR, 0, ts1}
r2 := Reloc{3, 8, objabi.R_CALL, 0, ts2}
r3 := Reloc{7, 1, objabi.R_USETYPE, 0, ts3}
sb1.AddReloc(r1)
sb1.AddReloc(r2)
sb2.AddReloc(r3)
// Add some data to the symbols.
d1 := []byte{1, 2, 3}
d2 := []byte{4, 5, 6, 7}
sb1.AddBytes(d1)
sb2.AddBytes(d2)
// Now invoke the usual loader interfaces to make sure
// we're getting the right things back for these symbols.
// First relocations...
expRel := [][]Reloc{[]Reloc{r1, r2}, []Reloc{r3}}
for k, sb := range []*SymbolBuilder{sb1, sb2} {
rsl := sb.Relocs()
exp := expRel[k]
if !sameRelocSlice(rsl, exp) {
t.Errorf("expected relocs %v, got %v", exp, rsl)
}
relocs := ldr.Relocs(sb.Sym())
r0 := relocs.At(0)
if r0 != exp[0] {
t.Errorf("expected reloc %v, got %v", exp[0], r0)
}
}
// ... then data.
dat := sb2.Data()
if bytes.Compare(dat, d2) != 0 {
t.Errorf("expected es2 data %v, got %v", d2, dat)
}
// Nameless symbol should still be nameless.
es3name := ldr.RawSymName(es3)
if "" != es3name {
t.Errorf("expected es3 name of '', got '%s'", es3name)
}
// Read value of materialized symbol.
es1val := sb1.Value()
if 0 != es1val {
t.Errorf("expected es1 value of 0, got %v", es1val)
}
// Test other misc methods
irm := ldr.IsReflectMethod(es1)
if 0 != es1val {
t.Errorf("expected IsReflectMethod(es1) value of 0, got %v", irm)
}
// Writing data to a materialized symbol should mark it reachable.
if !sb1.Reachable() || !sb2.Reachable() {
t.Fatalf("written-to materialized symbols should be reachable")
}
}
func sameRelocSlice(s1 []Reloc, s2 []Reloc) bool {
if len(s1) != len(s2) {
return false
}
for i := 0; i < len(s1); i++ {
if s1[i] != s2[i] {
return false
}
}
return true
}
type addFunc func(l *Loader, s Sym, s2 Sym)
func TestAddDataMethods(t *testing.T) {
edummy := func(s *sym.Symbol, str string, off int) {}
ldr := NewLoader(0, edummy)
dummyOreader := oReader{version: -1}
or := &dummyOreader
// Populate loader with some symbols.
addDummyObjSym(t, ldr, or, "type.uint8")
ldr.AddExtSym("hello", 0)
arch := sys.ArchAMD64
var testpoints = []struct {
which string
addDataFunc addFunc
expData []byte
expKind sym.SymKind
expRel []Reloc
}{
{
which: "AddUint8",
addDataFunc: func(l *Loader, s Sym, _ Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddUint8('a')
},
expData: []byte{'a'},
expKind: sym.SDATA,
},
{
which: "AddUintXX",
addDataFunc: func(l *Loader, s Sym, _ Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddUintXX(arch, 25185, 2)
},
expData: []byte{'a', 'b'},
expKind: sym.SDATA,
},
{
which: "SetUint8",
addDataFunc: func(l *Loader, s Sym, _ Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddUint8('a')
sb.AddUint8('b')
sb.SetUint8(arch, 1, 'c')
},
expData: []byte{'a', 'c'},
expKind: sym.SDATA,
},
{
which: "AddString",
addDataFunc: func(l *Loader, s Sym, _ Sym) {
sb := l.MakeSymbolUpdater(s)
sb.Addstring("hello")
},
expData: []byte{'h', 'e', 'l', 'l', 'o', 0},
expKind: sym.SNOPTRDATA,
},
{
which: "AddAddrPlus",
addDataFunc: func(l *Loader, s Sym, s2 Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddAddrPlus(arch, s2, 3)
},
expData: []byte{0, 0, 0, 0, 0, 0, 0, 0},
expKind: sym.SDATA,
expRel: []Reloc{Reloc{Type: objabi.R_ADDR, Size: 8, Add: 3, Sym: 6}},
},
{
which: "AddAddrPlus4",
addDataFunc: func(l *Loader, s Sym, s2 Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddAddrPlus4(arch, s2, 3)
},
expData: []byte{0, 0, 0, 0},
expKind: sym.SDATA,
expRel: []Reloc{Reloc{Type: objabi.R_ADDR, Size: 4, Add: 3, Sym: 7}},
},
{
which: "AddCURelativeAddrPlus",
addDataFunc: func(l *Loader, s Sym, s2 Sym) {
sb := l.MakeSymbolUpdater(s)
sb.AddCURelativeAddrPlus(arch, s2, 7)
},
expData: []byte{0, 0, 0, 0, 0, 0, 0, 0},
expKind: sym.SDATA,
expRel: []Reloc{Reloc{Type: objabi.R_ADDRCUOFF, Size: 8, Add: 7, Sym: 8}},
},
}
var pmi Sym
for k, tp := range testpoints {
name := fmt.Sprintf("new%d", k+1)
mi := ldr.AddExtSym(name, 0)
if mi == 0 {
t.Fatalf("AddExtSym failed for '" + name + "'")
}
tp.addDataFunc(ldr, mi, pmi)
if ldr.SymType(mi) != tp.expKind {
t.Errorf("testing Loader.%s: expected kind %s got %s",
tp.which, tp.expKind, ldr.SymType(mi))
}
if bytes.Compare(ldr.Data(mi), tp.expData) != 0 {
t.Errorf("testing Loader.%s: expected data %v got %v",
tp.which, tp.expData, ldr.Data(mi))
}
if !ldr.AttrReachable(mi) {
t.Fatalf("testing Loader.%s: sym updated should be reachable", tp.which)
}
relocs := ldr.Relocs(mi)
rsl := relocs.ReadAll(nil)
if !sameRelocSlice(rsl, tp.expRel) {
t.Fatalf("testing Loader.%s: got relocslice %+v wanted %+v",
tp.which, rsl, tp.expRel)
}
pmi = mi
}
}
func TestOuterSub(t *testing.T) {
ldr := NewLoader(0)
edummy := func(s *sym.Symbol, str string, off int) {}
ldr := NewLoader(0, edummy)
dummyOreader := oReader{version: -1}
or := &dummyOreader

250
src/cmd/link/internal/loader/symbolbuilder.go Normal file
View File

@ -0,0 +1,250 @@
// 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/objabi"
"cmd/internal/sys"
"cmd/link/internal/sym"
)
// 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
}
// NewSymbolBuilder 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.CreateExtSym(name)
if l.Syms[symIdx] != nil {
panic("can't build if sym.Symbol already present")
}
sb := &SymbolBuilder{l: l, symIdx: symIdx}
sb.extSymPayload = &l.payloads[symIdx-l.extStart]
return sb
}
// NewSymbolBuilder creates a symbol builder helper for an already-allocated
// external symbol 'symIdx'.
func (l *Loader) MakeSymbolUpdater(symIdx Sym) *SymbolBuilder {
if !l.IsExternal(symIdx) {
panic("can't build on non-external sym")
}
if l.Syms[symIdx] != nil {
panic("can't build if sym.Symbol already present")
}
sb := &SymbolBuilder{l: l, symIdx: symIdx}
sb.extSymPayload = &l.payloads[symIdx-l.extStart]
return sb
}
// 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) Extname() string { return sb.l.SymExtname(sb.symIdx) }
func (sb *SymbolBuilder) Dynimplib() string { return sb.l.SymDynimplib(sb.symIdx) }
func (sb *SymbolBuilder) Dynimpvers() string { return sb.l.SymDynimpvers(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) 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) AddBytes(data []byte) {
sb.setReachable()
if sb.kind == 0 {
sb.kind = sym.SDATA
}
sb.data = append(sb.data, data...)
sb.size = int64(len(sb.data))
}
func (sb *SymbolBuilder) Relocs() []Reloc {
return sb.relocs
}
func (sb *SymbolBuilder) SetRelocs(rslice []Reloc) {
sb.relocs = rslice
}
func (sb *SymbolBuilder) AddReloc(r Reloc) {
sb.relocs = append(sb.relocs, r)
}
func (sb *SymbolBuilder) Reachable() bool {
return sb.l.AttrReachable(sb.symIdx)
}
func (sb *SymbolBuilder) setReachable() {
sb.l.SetAttrReachable(sb.symIdx, true)
}
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) PrependSub(sub Sym) {
sb.l.PrependSub(sb.symIdx, sub)
}
func (sb *SymbolBuilder) AddUint8(v uint8) int64 {
off := sb.size
if sb.kind == 0 {
sb.kind = sym.SDATA
}
sb.setReachable()
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.setReachable()
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 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 1)
}
func (sb *SymbolBuilder) SetUint16(arch *sys.Arch, r int64, v uint16) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 2)
}
func (sb *SymbolBuilder) SetUint32(arch *sys.Arch, r int64, v uint32) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 4)
}
func (sb *SymbolBuilder) SetUint(arch *sys.Arch, r int64, v uint64) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, v, int64(arch.PtrSize))
}
func (sb *SymbolBuilder) Addstring(str string) int64 {
sb.setReachable()
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(nil, 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) addRel() *Reloc {
sb.relocs = append(sb.relocs, Reloc{})
return &sb.relocs[len(sb.relocs)-1]
}
func (sb *SymbolBuilder) addAddrPlus(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()
r.Sym = tgt
r.Off = int32(i)
r.Size = uint8(rsize)
r.Type = typ
r.Add = add
return i + int64(r.Size)
}
func (sb *SymbolBuilder) AddAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addAddrPlus(tgt, add, objabi.R_ADDR, arch.PtrSize)
}
func (sb *SymbolBuilder) AddAddrPlus4(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addAddrPlus(tgt, add, objabi.R_ADDR, 4)
}
func (sb *SymbolBuilder) AddCURelativeAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addAddrPlus(tgt, add, objabi.R_ADDRCUOFF, arch.PtrSize)
}