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cmd/link: move Plt, Got fields in sym.Symbol to cold section
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The sym.Symbol 'Plt' and 'Got' field are used only with cgo and/or
external linking and are not needed for most symbols. Relocate them to
sym.AuxSymbol so as to shrink the main Symbol struct.

Updates #26186

Change-Id: I170d628a760be300a0c1f738f0998970e91ce3d6
Reviewed-on: https://go-review.googlesource.com/125478
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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@thanm
thanm committed Aug 30, 2018
1 parent 2975914 commit f78cc13
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Showing 10 changed files with 100 additions and 68 deletions.
28 changes: 14 additions & 14 deletions src/cmd/link/internal/amd64/asm.go
View file
Expand Up @@ -139,7 +139,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
if targ.Type == sym.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add += int64(targ.Plt)
r.Add += int64(targ.Plt())
}

return true
Expand All @@ -164,7 +164,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
r.Type = objabi.R_PCREL
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += 4
r.Add += int64(targ.Got)
r.Add += int64(targ.Got())
return true

case 256 + objabi.RelocType(elf.R_X86_64_64):
Expand All @@ -190,7 +190,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
if targ.Type == sym.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
r.Type = objabi.R_PCREL
return true
}
Expand Down Expand Up @@ -230,7 +230,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
addgotsym(ctxt, targ)
r.Type = objabi.R_PCREL
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += int64(targ.Got)
r.Add += int64(targ.Got())
return true
}

Expand All @@ -249,15 +249,15 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
// Build a PLT entry and change the relocation target to that entry.
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
return true

case objabi.R_ADDR:
if s.Type == sym.STEXT && ctxt.IsELF {
if ctxt.HeadType == objabi.Hsolaris {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add += int64(targ.Plt)
r.Add += int64(targ.Plt())
return true
}
// The code is asking for the address of an external
Expand All @@ -266,7 +266,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
addgotsym(ctxt, targ)

r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += int64(targ.Got)
r.Add += int64(targ.Got())
return true
}

Expand Down Expand Up @@ -567,7 +567,7 @@ func elfsetupplt(ctxt *ld.Link) {
}

func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
if s.Plt >= 0 {
if s.Plt() >= 0 {
return
}

Expand Down Expand Up @@ -606,7 +606,7 @@ func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
rela.AddUint64(ctxt.Arch, ld.ELF64_R_INFO(uint32(s.Dynid), uint32(elf.R_X86_64_JMP_SLOT)))
rela.AddUint64(ctxt.Arch, 0)

s.Plt = int32(plt.Size - 16)
s.SetPlt(int32(plt.Size - 16))
} else if ctxt.HeadType == objabi.Hdarwin {
// To do lazy symbol lookup right, we're supposed
// to tell the dynamic loader which library each
Expand All @@ -624,29 +624,29 @@ func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
ctxt.Syms.Lookup(".linkedit.plt", 0).AddUint32(ctxt.Arch, uint32(s.Dynid))

// jmpq *got+size(IP)
s.Plt = int32(plt.Size)
s.SetPlt(int32(plt.Size))

plt.AddUint8(0xff)
plt.AddUint8(0x25)
plt.AddPCRelPlus(ctxt.Arch, ctxt.Syms.Lookup(".got", 0), int64(s.Got))
plt.AddPCRelPlus(ctxt.Arch, ctxt.Syms.Lookup(".got", 0), int64(s.Got()))
} else {
ld.Errorf(s, "addpltsym: unsupported binary format")
}
}

func addgotsym(ctxt *ld.Link, s *sym.Symbol) {
if s.Got >= 0 {
if s.Got() >= 0 {
return
}

ld.Adddynsym(ctxt, s)
got := ctxt.Syms.Lookup(".got", 0)
s.Got = int32(got.Size)
s.SetGot(int32(got.Size))
got.AddUint64(ctxt.Arch, 0)

if ctxt.IsELF {
rela := ctxt.Syms.Lookup(".rela", 0)
rela.AddAddrPlus(ctxt.Arch, got, int64(s.Got))
rela.AddAddrPlus(ctxt.Arch, got, int64(s.Got()))
rela.AddUint64(ctxt.Arch, ld.ELF64_R_INFO(uint32(s.Dynid), uint32(elf.R_X86_64_GLOB_DAT)))
rela.AddUint64(ctxt.Arch, 0)
} else if ctxt.HeadType == objabi.Hdarwin {
Expand Down
32 changes: 16 additions & 16 deletions src/cmd/link/internal/arm/asm.go
View file
Expand Up @@ -132,7 +132,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
if targ.Type == sym.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
}

return true
Expand All @@ -150,7 +150,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {

r.Type = objabi.R_CONST // write r->add during relocsym
r.Sym = nil
r.Add += int64(targ.Got)
r.Add += int64(targ.Got())
return true

case 256 + objabi.RelocType(elf.R_ARM_GOT_PREL): // GOT(nil) + A - nil
Expand All @@ -162,7 +162,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {

r.Type = objabi.R_PCREL
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += int64(targ.Got) + 4
r.Add += int64(targ.Got()) + 4
return true

case 256 + objabi.RelocType(elf.R_ARM_GOTOFF): // R_ARM_GOTOFF32
Expand All @@ -182,7 +182,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
if targ.Type == sym.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
}

return true
Expand Down Expand Up @@ -216,7 +216,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
if targ.Type == sym.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
}

return true
Expand All @@ -235,7 +235,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
}
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
return true

case objabi.R_ADDR:
Expand Down Expand Up @@ -678,15 +678,15 @@ func addpltreloc(ctxt *ld.Link, plt *sym.Symbol, got *sym.Symbol, s *sym.Symbol,
r.Off = int32(plt.Size)
r.Siz = 4
r.Type = typ
r.Add = int64(s.Got) - 8
r.Add = int64(s.Got()) - 8

plt.Attr |= sym.AttrReachable
plt.Size += 4
plt.Grow(plt.Size)
}

func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
if s.Plt >= 0 {
if s.Plt() >= 0 {
return
}

Expand All @@ -701,22 +701,22 @@ func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
}

// .got entry
s.Got = int32(got.Size)
s.SetGot(int32(got.Size))

// In theory, all GOT should point to the first PLT entry,
// Linux/ARM's dynamic linker will do that for us, but FreeBSD/ARM's
// dynamic linker won't, so we'd better do it ourselves.
got.AddAddrPlus(ctxt.Arch, plt, 0)

// .plt entry, this depends on the .got entry
s.Plt = int32(plt.Size)
s.SetPlt(int32(plt.Size))

addpltreloc(ctxt, plt, got, s, objabi.R_PLT0) // add lr, pc, #0xXX00000
addpltreloc(ctxt, plt, got, s, objabi.R_PLT1) // add lr, lr, #0xYY000
addpltreloc(ctxt, plt, got, s, objabi.R_PLT2) // ldr pc, [lr, #0xZZZ]!

// rel
rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got))
rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got()))

rel.AddUint32(ctxt.Arch, ld.ELF32_R_INFO(uint32(s.Dynid), uint32(elf.R_ARM_JUMP_SLOT)))
} else {
Expand All @@ -725,12 +725,12 @@ func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
}

func addgotsyminternal(ctxt *ld.Link, s *sym.Symbol) {
if s.Got >= 0 {
if s.Got() >= 0 {
return
}

got := ctxt.Syms.Lookup(".got", 0)
s.Got = int32(got.Size)
s.SetGot(int32(got.Size))

got.AddAddrPlus(ctxt.Arch, s, 0)

Expand All @@ -741,18 +741,18 @@ func addgotsyminternal(ctxt *ld.Link, s *sym.Symbol) {
}

func addgotsym(ctxt *ld.Link, s *sym.Symbol) {
if s.Got >= 0 {
if s.Got() >= 0 {
return
}

ld.Adddynsym(ctxt, s)
got := ctxt.Syms.Lookup(".got", 0)
s.Got = int32(got.Size)
s.SetGot(int32(got.Size))
got.AddUint32(ctxt.Arch, 0)

if ctxt.IsELF {
rel := ctxt.Syms.Lookup(".rel", 0)
rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got))
rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got()))
rel.AddUint32(ctxt.Arch, ld.ELF32_R_INFO(uint32(s.Dynid), uint32(elf.R_ARM_GLOB_DAT)))
} else {
ld.Errorf(s, "addgotsym: unsupported binary format")
Expand Down
10 changes: 5 additions & 5 deletions src/cmd/link/internal/ld/data.go
View file
Expand Up @@ -546,10 +546,10 @@ func windynrelocsym(ctxt *Link, s *sym.Symbol) {
}
Errorf(s, "dynamic relocation to unreachable symbol %s", targ.Name)
}
if r.Sym.Plt == -2 && r.Sym.Got != -2 { // make dynimport JMP table for PE object files.
targ.Plt = int32(rel.Size)
if r.Sym.Plt() == -2 && r.Sym.Got() != -2 { // make dynimport JMP table for PE object files.
targ.SetPlt(int32(rel.Size))
r.Sym = rel
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())

// jmp *addr
switch ctxt.Arch.Family {
Expand All @@ -569,9 +569,9 @@ func windynrelocsym(ctxt *Link, s *sym.Symbol) {
rel.AddAddrPlus4(targ, 0)
rel.AddUint8(0x90)
}
} else if r.Sym.Plt >= 0 {
} else if r.Sym.Plt() >= 0 {
r.Sym = rel
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
}
}
}
Expand Down
4 changes: 2 additions & 2 deletions src/cmd/link/internal/loadpe/ldpe.go
View file
Expand Up @@ -358,7 +358,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng

if pesym.SectionNumber == 0 { // extern
if s.Type == sym.SDYNIMPORT {
s.Plt = -2 // flag for dynimport in PE object files.
s.SetPlt(-2) // flag for dynimport in PE object files.
}
if s.Type == sym.SXREF && pesym.Value > 0 { // global data
s.Type = sym.SNOPTRDATA
Expand Down Expand Up @@ -479,7 +479,7 @@ func readpesym(arch *sys.Arch, syms *sym.Symbols, f *pe.File, pesym *pe.COFFSymb
s.Type = sym.SXREF
}
if strings.HasPrefix(symname, "__imp_") {
s.Got = -2 // flag for __imp_
s.SetGot(-2) // flag for __imp_
}

return s, nil
Expand Down
10 changes: 5 additions & 5 deletions src/cmd/link/internal/ppc64/asm.go
View file
Expand Up @@ -236,7 +236,7 @@ func gencallstub(ctxt *ld.Link, abicase int, stub *sym.Symbol, targ *sym.Symbol)

r.Off = int32(stub.Size)
r.Sym = plt
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
r.Siz = 2
if ctxt.Arch.ByteOrder == binary.BigEndian {
r.Off += int32(r.Siz)
Expand All @@ -247,7 +247,7 @@ func gencallstub(ctxt *ld.Link, abicase int, stub *sym.Symbol, targ *sym.Symbol)
r = stub.AddRel()
r.Off = int32(stub.Size)
r.Sym = plt
r.Add = int64(targ.Plt)
r.Add = int64(targ.Plt())
r.Siz = 2
if ctxt.Arch.ByteOrder == binary.BigEndian {
r.Off += int32(r.Siz)
Expand Down Expand Up @@ -793,7 +793,7 @@ overflow:
}

func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
if s.Plt >= 0 {
if s.Plt() >= 0 {
return
}

Expand Down Expand Up @@ -825,11 +825,11 @@ func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
// JMP_SLOT dynamic relocation for it.
//
// TODO(austin): ABI v1 is different
s.Plt = int32(plt.Size)
s.SetPlt(int32(plt.Size))

plt.Size += 8

rela.AddAddrPlus(ctxt.Arch, plt, int64(s.Plt))
rela.AddAddrPlus(ctxt.Arch, plt, int64(s.Plt()))
rela.AddUint64(ctxt.Arch, ld.ELF64_R_INFO(uint32(s.Dynid), uint32(elf.R_PPC64_JMP_SLOT)))
rela.AddUint64(ctxt.Arch, 0)
} else {
Expand Down

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