Golang程序
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// Copyright 2009 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 ld
import (
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/sym"
"sort"
"strings"
)
type MachoHdr struct {
cpu uint32
subcpu uint32
}
type MachoSect struct {
name string
segname string
addr uint64
size uint64
off uint32
align uint32
reloc uint32
nreloc uint32
flag uint32
res1 uint32
res2 uint32
}
type MachoSeg struct {
name string
vsize uint64
vaddr uint64
fileoffset uint64
filesize uint64
prot1 uint32
prot2 uint32
nsect uint32
msect uint32
sect []MachoSect
flag uint32
}
type MachoLoad struct {
type_ uint32
data []uint32
}
/*
* Total amount of space to reserve at the start of the file
* for Header, PHeaders, and SHeaders.
* May waste some.
*/
const (
INITIAL_MACHO_HEADR = 4 * 1024
)
const (
MACHO_CPU_AMD64 = 1<<24 | 7
MACHO_CPU_386 = 7
MACHO_SUBCPU_X86 = 3
MACHO_CPU_ARM = 12
MACHO_SUBCPU_ARM = 0
MACHO_SUBCPU_ARMV7 = 9
MACHO_CPU_ARM64 = 1<<24 | 12
MACHO_SUBCPU_ARM64_ALL = 0
MACHO32SYMSIZE = 12
MACHO64SYMSIZE = 16
MACHO_X86_64_RELOC_UNSIGNED = 0
MACHO_X86_64_RELOC_SIGNED = 1
MACHO_X86_64_RELOC_BRANCH = 2
MACHO_X86_64_RELOC_GOT_LOAD = 3
MACHO_X86_64_RELOC_GOT = 4
MACHO_X86_64_RELOC_SUBTRACTOR = 5
MACHO_X86_64_RELOC_SIGNED_1 = 6
MACHO_X86_64_RELOC_SIGNED_2 = 7
MACHO_X86_64_RELOC_SIGNED_4 = 8
MACHO_ARM_RELOC_VANILLA = 0
MACHO_ARM_RELOC_PAIR = 1
MACHO_ARM_RELOC_SECTDIFF = 2
MACHO_ARM_RELOC_BR24 = 5
MACHO_ARM64_RELOC_UNSIGNED = 0
MACHO_ARM64_RELOC_BRANCH26 = 2
MACHO_ARM64_RELOC_PAGE21 = 3
MACHO_ARM64_RELOC_PAGEOFF12 = 4
MACHO_ARM64_RELOC_ADDEND = 10
MACHO_GENERIC_RELOC_VANILLA = 0
MACHO_FAKE_GOTPCREL = 100
)
const (
MH_MAGIC = 0xfeedface
MH_MAGIC_64 = 0xfeedfacf
MH_OBJECT = 0x1
MH_EXECUTE = 0x2
MH_NOUNDEFS = 0x1
)
const (
LC_SEGMENT = 0x1
LC_SYMTAB = 0x2
LC_UNIXTHREAD = 0x5
LC_DYSYMTAB = 0xb
LC_LOAD_DYLIB = 0xc
LC_ID_DYLIB = 0xd
LC_LOAD_DYLINKER = 0xe
LC_PREBOUND_DYLIB = 0x10
LC_LOAD_WEAK_DYLIB = 0x18
LC_SEGMENT_64 = 0x19
LC_UUID = 0x1b
LC_RPATH = 0x8000001c
LC_CODE_SIGNATURE = 0x1d
LC_SEGMENT_SPLIT_INFO = 0x1e
LC_REEXPORT_DYLIB = 0x8000001f
LC_ENCRYPTION_INFO = 0x21
LC_DYLD_INFO = 0x22
LC_DYLD_INFO_ONLY = 0x80000022
LC_VERSION_MIN_MACOSX = 0x24
LC_VERSION_MIN_IPHONEOS = 0x25
LC_FUNCTION_STARTS = 0x26
LC_MAIN = 0x80000028
LC_DATA_IN_CODE = 0x29
LC_SOURCE_VERSION = 0x2A
LC_DYLIB_CODE_SIGN_DRS = 0x2B
LC_ENCRYPTION_INFO_64 = 0x2C
)
const (
S_REGULAR = 0x0
S_ZEROFILL = 0x1
S_NON_LAZY_SYMBOL_POINTERS = 0x6
S_SYMBOL_STUBS = 0x8
S_MOD_INIT_FUNC_POINTERS = 0x9
S_ATTR_PURE_INSTRUCTIONS = 0x80000000
S_ATTR_DEBUG = 0x02000000
S_ATTR_SOME_INSTRUCTIONS = 0x00000400
)
// Copyright 2009 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.
// Mach-O file writing
// http://developer.apple.com/mac/library/DOCUMENTATION/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html
var machohdr MachoHdr
var load []MachoLoad
var seg [16]MachoSeg
var nseg int
var ndebug int
var nsect int
const (
SymKindLocal = 0 + iota
SymKindExtdef
SymKindUndef
NumSymKind
)
var nkind [NumSymKind]int
var sortsym []*sym.Symbol
var nsortsym int
// Amount of space left for adding load commands
// that refer to dynamic libraries. Because these have
// to go in the Mach-O header, we can't just pick a
// "big enough" header size. The initial header is
// one page, the non-dynamic library stuff takes
// up about 1300 bytes; we overestimate that as 2k.
var loadBudget = INITIAL_MACHO_HEADR - 2*1024
func getMachoHdr() *MachoHdr {
return &machohdr
}
func newMachoLoad(arch *sys.Arch, type_ uint32, ndata uint32) *MachoLoad {
if arch.PtrSize == 8 && (ndata&1 != 0) {
ndata++
}
load = append(load, MachoLoad{})
l := &load[len(load)-1]
l.type_ = type_
l.data = make([]uint32, ndata)
return l
}
func newMachoSeg(name string, msect int) *MachoSeg {
if nseg >= len(seg) {
Exitf("too many segs")
}
s := &seg[nseg]
nseg++
s.name = name
s.msect = uint32(msect)
s.sect = make([]MachoSect, msect)
return s
}
func newMachoSect(seg *MachoSeg, name string, segname string) *MachoSect {
if seg.nsect >= seg.msect {
Exitf("too many sects in segment %s", seg.name)
}
s := &seg.sect[seg.nsect]
seg.nsect++
s.name = name
s.segname = segname
nsect++
return s
}
// Generic linking code.
var dylib []string
var linkoff int64
func machowrite(arch *sys.Arch, out *OutBuf, linkmode LinkMode) int {
o1 := out.Offset()
loadsize := 4 * 4 * ndebug
for i := 0; i < len(load); i++ {
loadsize += 4 * (len(load[i].data) + 2)
}
if arch.PtrSize == 8 {
loadsize += 18 * 4 * nseg
loadsize += 20 * 4 * nsect
} else {
loadsize += 14 * 4 * nseg
loadsize += 17 * 4 * nsect
}
if arch.PtrSize == 8 {
out.Write32(MH_MAGIC_64)
} else {
out.Write32(MH_MAGIC)
}
out.Write32(machohdr.cpu)
out.Write32(machohdr.subcpu)
if linkmode == LinkExternal {
out.Write32(MH_OBJECT) /* file type - mach object */
} else {
out.Write32(MH_EXECUTE) /* file type - mach executable */
}
out.Write32(uint32(len(load)) + uint32(nseg) + uint32(ndebug))
out.Write32(uint32(loadsize))
if nkind[SymKindUndef] == 0 {
out.Write32(MH_NOUNDEFS) /* flags - no undefines */
} else {
out.Write32(0) /* flags */
}
if arch.PtrSize == 8 {
out.Write32(0) /* reserved */
}
for i := 0; i < nseg; i++ {
s := &seg[i]
if arch.PtrSize == 8 {
out.Write32(LC_SEGMENT_64)
out.Write32(72 + 80*s.nsect)
out.WriteStringN(s.name, 16)
out.Write64(s.vaddr)
out.Write64(s.vsize)
out.Write64(s.fileoffset)
out.Write64(s.filesize)
out.Write32(s.prot1)
out.Write32(s.prot2)
out.Write32(s.nsect)
out.Write32(s.flag)
} else {
out.Write32(LC_SEGMENT)
out.Write32(56 + 68*s.nsect)
out.WriteStringN(s.name, 16)
out.Write32(uint32(s.vaddr))
out.Write32(uint32(s.vsize))
out.Write32(uint32(s.fileoffset))
out.Write32(uint32(s.filesize))
out.Write32(s.prot1)
out.Write32(s.prot2)
out.Write32(s.nsect)
out.Write32(s.flag)
}
for j := uint32(0); j < s.nsect; j++ {
t := &s.sect[j]
if arch.PtrSize == 8 {
out.WriteStringN(t.name, 16)
out.WriteStringN(t.segname, 16)
out.Write64(t.addr)
out.Write64(t.size)
out.Write32(t.off)
out.Write32(t.align)
out.Write32(t.reloc)
out.Write32(t.nreloc)
out.Write32(t.flag)
out.Write32(t.res1) /* reserved */
out.Write32(t.res2) /* reserved */
out.Write32(0) /* reserved */
} else {
out.WriteStringN(t.name, 16)
out.WriteStringN(t.segname, 16)
out.Write32(uint32(t.addr))
out.Write32(uint32(t.size))
out.Write32(t.off)
out.Write32(t.align)
out.Write32(t.reloc)
out.Write32(t.nreloc)
out.Write32(t.flag)
out.Write32(t.res1) /* reserved */
out.Write32(t.res2) /* reserved */
}
}
}
for i := 0; i < len(load); i++ {
l := &load[i]
out.Write32(l.type_)
out.Write32(4 * (uint32(len(l.data)) + 2))
for j := 0; j < len(l.data); j++ {
out.Write32(l.data[j])
}
}
return int(out.Offset() - o1)
}
func (ctxt *Link) domacho() {
if *FlagD {
return
}
// empirically, string table must begin with " \x00".
s := ctxt.Syms.Lookup(".machosymstr", 0)
s.Type = sym.SMACHOSYMSTR
s.Attr |= sym.AttrReachable
s.AddUint8(' ')
s.AddUint8('\x00')
s = ctxt.Syms.Lookup(".machosymtab", 0)
s.Type = sym.SMACHOSYMTAB
s.Attr |= sym.AttrReachable
if ctxt.LinkMode != LinkExternal {
s := ctxt.Syms.Lookup(".plt", 0) // will be __symbol_stub
s.Type = sym.SMACHOPLT
s.Attr |= sym.AttrReachable
s = ctxt.Syms.Lookup(".got", 0) // will be __nl_symbol_ptr
s.Type = sym.SMACHOGOT
s.Attr |= sym.AttrReachable
s.Align = 4
s = ctxt.Syms.Lookup(".linkedit.plt", 0) // indirect table for .plt
s.Type = sym.SMACHOINDIRECTPLT
s.Attr |= sym.AttrReachable
s = ctxt.Syms.Lookup(".linkedit.got", 0) // indirect table for .got
s.Type = sym.SMACHOINDIRECTGOT
s.Attr |= sym.AttrReachable
}
}
func machoadddynlib(lib string, linkmode LinkMode) {
if seenlib[lib] || linkmode == LinkExternal {
return
}
seenlib[lib] = true
// Will need to store the library name rounded up
// and 24 bytes of header metadata. If not enough
// space, grab another page of initial space at the
// beginning of the output file.
loadBudget -= (len(lib)+7)/8*8 + 24
if loadBudget < 0 {
HEADR += 4096
*FlagTextAddr += 4096
loadBudget += 4096
}
dylib = append(dylib, lib)
}
func machoshbits(ctxt *Link, mseg *MachoSeg, sect *sym.Section, segname string) {
buf := "__" + strings.Replace(sect.Name[1:], ".", "_", -1)
var msect *MachoSect
if sect.Rwx&1 == 0 && segname != "__DWARF" && (ctxt.Arch.Family == sys.ARM64 ||
(ctxt.Arch.Family == sys.AMD64 && ctxt.BuildMode != BuildModeExe) ||
(ctxt.Arch.Family == sys.ARM && ctxt.BuildMode != BuildModeExe)) {
// Darwin external linker on arm64 and on amd64 and arm in c-shared/c-archive buildmode
// complains about absolute relocs in __TEXT, so if the section is not
// executable, put it in __DATA segment.
msect = newMachoSect(mseg, buf, "__DATA")
} else {
msect = newMachoSect(mseg, buf, segname)
}
if sect.Rellen > 0 {
msect.reloc = uint32(sect.Reloff)
msect.nreloc = uint32(sect.Rellen / 8)
}
for 1<<msect.align < sect.Align {
msect.align++
}
msect.addr = sect.Vaddr
msect.size = sect.Length
if sect.Vaddr < sect.Seg.Vaddr+sect.Seg.Filelen {
// data in file
if sect.Length > sect.Seg.Vaddr+sect.Seg.Filelen-sect.Vaddr {
Errorf(nil, "macho cannot represent section %s crossing data and bss", sect.Name)
}
msect.off = uint32(sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr)
} else {
msect.off = 0
msect.flag |= S_ZEROFILL
}
if sect.Rwx&1 != 0 {
msect.flag |= S_ATTR_SOME_INSTRUCTIONS
}
if sect.Name == ".plt" {
msect.name = "__symbol_stub1"
msect.flag = S_ATTR_PURE_INSTRUCTIONS | S_ATTR_SOME_INSTRUCTIONS | S_SYMBOL_STUBS
msect.res1 = 0 //nkind[SymKindLocal];
msect.res2 = 6
}
if sect.Name == ".got" {
msect.name = "__nl_symbol_ptr"
msect.flag = S_NON_LAZY_SYMBOL_POINTERS
msect.res1 = uint32(ctxt.Syms.Lookup(".linkedit.plt", 0).Size / 4) /* offset into indirect symbol table */
}
if sect.Name == ".init_array" {
msect.name = "__mod_init_func"
msect.flag = S_MOD_INIT_FUNC_POINTERS
}
if segname == "__DWARF" {
msect.flag |= S_ATTR_DEBUG
}
}
func Asmbmacho(ctxt *Link) {
/* apple MACH */
va := *FlagTextAddr - int64(HEADR)
mh := getMachoHdr()
switch ctxt.Arch.Family {
default:
Exitf("unknown macho architecture: %v", ctxt.Arch.Family)
case sys.ARM:
mh.cpu = MACHO_CPU_ARM
mh.subcpu = MACHO_SUBCPU_ARMV7
case sys.AMD64:
mh.cpu = MACHO_CPU_AMD64
mh.subcpu = MACHO_SUBCPU_X86
case sys.ARM64:
mh.cpu = MACHO_CPU_ARM64
mh.subcpu = MACHO_SUBCPU_ARM64_ALL
case sys.I386:
mh.cpu = MACHO_CPU_386
mh.subcpu = MACHO_SUBCPU_X86
}
var ms *MachoSeg
if ctxt.LinkMode == LinkExternal {
/* segment for entire file */
ms = newMachoSeg("", 40)
ms.fileoffset = Segtext.Fileoff
if ctxt.Arch.Family == sys.ARM || ctxt.BuildMode == BuildModeCArchive {
ms.filesize = Segdata.Fileoff + Segdata.Filelen - Segtext.Fileoff
} else {
ms.filesize = Segdwarf.Fileoff + Segdwarf.Filelen - Segtext.Fileoff
ms.vsize = Segdwarf.Vaddr + Segdwarf.Length - Segtext.Vaddr
}
}
/* segment for zero page */
if ctxt.LinkMode != LinkExternal {
ms = newMachoSeg("__PAGEZERO", 0)
ms.vsize = uint64(va)
}
/* text */
v := Rnd(int64(uint64(HEADR)+Segtext.Length), int64(*FlagRound))
if ctxt.LinkMode != LinkExternal {
ms = newMachoSeg("__TEXT", 20)
ms.vaddr = uint64(va)
ms.vsize = uint64(v)
ms.fileoffset = 0
ms.filesize = uint64(v)
ms.prot1 = 7
ms.prot2 = 5
}
for _, sect := range Segtext.Sections {
machoshbits(ctxt, ms, sect, "__TEXT")
}
/* data */
if ctxt.LinkMode != LinkExternal {
w := int64(Segdata.Length)
ms = newMachoSeg("__DATA", 20)
ms.vaddr = uint64(va) + uint64(v)
ms.vsize = uint64(w)
ms.fileoffset = uint64(v)
ms.filesize = Segdata.Filelen
ms.prot1 = 3
ms.prot2 = 3
}
for _, sect := range Segdata.Sections {
machoshbits(ctxt, ms, sect, "__DATA")
}
/* dwarf */
if !*FlagW {
if ctxt.LinkMode != LinkExternal {
ms = newMachoSeg("__DWARF", 20)
ms.vaddr = Segdwarf.Vaddr
ms.vsize = 0
ms.fileoffset = Segdwarf.Fileoff
ms.filesize = Segdwarf.Filelen
}
for _, sect := range Segdwarf.Sections {
machoshbits(ctxt, ms, sect, "__DWARF")
}
}
if ctxt.LinkMode != LinkExternal {
switch ctxt.Arch.Family {
default:
Exitf("unknown macho architecture: %v", ctxt.Arch.Family)
case sys.ARM:
ml := newMachoLoad(ctxt.Arch, LC_UNIXTHREAD, 17+2)
ml.data[0] = 1 /* thread type */
ml.data[1] = 17 /* word count */
ml.data[2+15] = uint32(Entryvalue(ctxt)) /* start pc */
case sys.AMD64:
ml := newMachoLoad(ctxt.Arch, LC_UNIXTHREAD, 42+2)
ml.data[0] = 4 /* thread type */
ml.data[1] = 42 /* word count */
ml.data[2+32] = uint32(Entryvalue(ctxt)) /* start pc */
ml.data[2+32+1] = uint32(Entryvalue(ctxt) >> 32)
case sys.ARM64:
ml := newMachoLoad(ctxt.Arch, LC_UNIXTHREAD, 68+2)
ml.data[0] = 6 /* thread type */
ml.data[1] = 68 /* word count */
ml.data[2+64] = uint32(Entryvalue(ctxt)) /* start pc */
ml.data[2+64+1] = uint32(Entryvalue(ctxt) >> 32)
case sys.I386:
ml := newMachoLoad(ctxt.Arch, LC_UNIXTHREAD, 16+2)
ml.data[0] = 1 /* thread type */
ml.data[1] = 16 /* word count */
ml.data[2+10] = uint32(Entryvalue(ctxt)) /* start pc */
}
}
if !*FlagD {
// must match domacholink below
s1 := ctxt.Syms.Lookup(".machosymtab", 0)
s2 := ctxt.Syms.Lookup(".linkedit.plt", 0)
s3 := ctxt.Syms.Lookup(".linkedit.got", 0)
s4 := ctxt.Syms.Lookup(".machosymstr", 0)
if ctxt.LinkMode != LinkExternal {
ms := newMachoSeg("__LINKEDIT", 0)
ms.vaddr = uint64(va) + uint64(v) + uint64(Rnd(int64(Segdata.Length), int64(*FlagRound)))
ms.vsize = uint64(s1.Size) + uint64(s2.Size) + uint64(s3.Size) + uint64(s4.Size)
ms.fileoffset = uint64(linkoff)
ms.filesize = ms.vsize
ms.prot1 = 7
ms.prot2 = 3
}
ml := newMachoLoad(ctxt.Arch, LC_SYMTAB, 4)
ml.data[0] = uint32(linkoff) /* symoff */
ml.data[1] = uint32(nsortsym) /* nsyms */
ml.data[2] = uint32(linkoff + s1.Size + s2.Size + s3.Size) /* stroff */
ml.data[3] = uint32(s4.Size) /* strsize */
machodysymtab(ctxt)
if ctxt.LinkMode != LinkExternal {
ml := newMachoLoad(ctxt.Arch, LC_LOAD_DYLINKER, 6)
ml.data[0] = 12 /* offset to string */
stringtouint32(ml.data[1:], "/usr/lib/dyld")
for i := 0; i < len(dylib); i++ {
ml = newMachoLoad(ctxt.Arch, LC_LOAD_DYLIB, 4+(uint32(len(dylib[i]))+1+7)/8*2)
ml.data[0] = 24 /* offset of string from beginning of load */
ml.data[1] = 0 /* time stamp */
ml.data[2] = 0 /* version */
ml.data[3] = 0 /* compatibility version */
stringtouint32(ml.data[4:], dylib[i])
}
}
}
if ctxt.LinkMode == LinkInternal {
// For lldb, must say LC_VERSION_MIN_MACOSX or else
// it won't know that this Mach-O binary is from OS X
// (could be iOS or WatchOS instead).
// Go on iOS uses linkmode=external, and linkmode=external
// adds this itself. So we only need this code for linkmode=internal
// and we can assume OS X.
//
// See golang.org/issues/12941.
ml := newMachoLoad(ctxt.Arch, LC_VERSION_MIN_MACOSX, 2)
ml.data[0] = 10<<16 | 7<<8 | 0<<0 // OS X version 10.7.0
ml.data[1] = 10<<16 | 7<<8 | 0<<0 // SDK 10.7.0
}
a := machowrite(ctxt.Arch, ctxt.Out, ctxt.LinkMode)
if int32(a) > HEADR {
Exitf("HEADR too small: %d > %d", a, HEADR)
}
}
func symkind(s *sym.Symbol) int {
if s.Type == sym.SDYNIMPORT {
return SymKindUndef
}
if s.Attr.CgoExport() {
return SymKindExtdef
}
return SymKindLocal
}
func addsym(ctxt *Link, s *sym.Symbol, name string, type_ SymbolType, addr int64, gotype *sym.Symbol) {
if s == nil {
return
}
switch type_ {
default:
return
case DataSym, BSSSym, TextSym:
break
}
if sortsym != nil {
sortsym[nsortsym] = s
nkind[symkind(s)]++
}
nsortsym++
}
type machoscmp []*sym.Symbol
func (x machoscmp) Len() int {
return len(x)
}
func (x machoscmp) Swap(i, j int) {
x[i], x[j] = x[j], x[i]
}
func (x machoscmp) Less(i, j int) bool {
s1 := x[i]
s2 := x[j]
k1 := symkind(s1)
k2 := symkind(s2)
if k1 != k2 {
return k1 < k2
}
return s1.Extname < s2.Extname
}
func machogenasmsym(ctxt *Link) {
genasmsym(ctxt, addsym)
for _, s := range ctxt.Syms.Allsym {
if s.Type == sym.SDYNIMPORT || s.Type == sym.SHOSTOBJ {
if s.Attr.Reachable() {
addsym(ctxt, s, "", DataSym, 0, nil)
}
}
}
}
func machosymorder(ctxt *Link) {
// On Mac OS X Mountain Lion, we must sort exported symbols
// So we sort them here and pre-allocate dynid for them
// See https://golang.org/issue/4029
for i := 0; i < len(dynexp); i++ {
dynexp[i].Attr |= sym.AttrReachable
}
machogenasmsym(ctxt)
sortsym = make([]*sym.Symbol, nsortsym)
nsortsym = 0
machogenasmsym(ctxt)
sort.Sort(machoscmp(sortsym[:nsortsym]))
for i := 0; i < nsortsym; i++ {
sortsym[i].Dynid = int32(i)
}
}
// machoShouldExport reports whether a symbol needs to be exported.
//
// When dynamically linking, all non-local variables and plugin-exported
// symbols need to be exported.
func machoShouldExport(ctxt *Link, s *sym.Symbol) bool {
if !ctxt.DynlinkingGo() || s.Attr.Local() {
return false
}
if ctxt.BuildMode == BuildModePlugin && strings.HasPrefix(s.Extname, objabi.PathToPrefix(*flagPluginPath)) {
return true
}
if strings.HasPrefix(s.Name, "go.itab.") {
return true
}
if strings.HasPrefix(s.Name, "type.") && !strings.HasPrefix(s.Name, "type..") {
// reduce runtime typemap pressure, but do not
// export alg functions (type..*), as these
// appear in pclntable.
return true
}
if strings.HasPrefix(s.Name, "go.link.pkghash") {
return true
}
return s.Type >= sym.SELFSECT // only writable sections
}
func machosymtab(ctxt *Link) {
symtab := ctxt.Syms.Lookup(".machosymtab", 0)
symstr := ctxt.Syms.Lookup(".machosymstr", 0)
for i := 0; i < nsortsym; i++ {
s := sortsym[i]
symtab.AddUint32(ctxt.Arch, uint32(symstr.Size))
export := machoShouldExport(ctxt, s)
// In normal buildmodes, only add _ to C symbols, as
// Go symbols have dot in the name.
//
// Do not export C symbols in plugins, as runtime C
// symbols like crosscall2 are in pclntab and end up
// pointing at the host binary, breaking unwinding.
// See Issue #18190.
cexport := !strings.Contains(s.Extname, ".") && (ctxt.BuildMode != BuildModePlugin || onlycsymbol(s))
if cexport || export {
symstr.AddUint8('_')
}
// replace "·" as ".", because DTrace cannot handle it.
Addstring(symstr, strings.Replace(s.Extname, "·", ".", -1))
if s.Type == sym.SDYNIMPORT || s.Type == sym.SHOSTOBJ {
symtab.AddUint8(0x01) // type N_EXT, external symbol
symtab.AddUint8(0) // no section
symtab.AddUint16(ctxt.Arch, 0) // desc
symtab.AddUintXX(ctxt.Arch, 0, ctxt.Arch.PtrSize) // no value
} else {
if s.Attr.CgoExport() || export {
symtab.AddUint8(0x0f)
} else {
symtab.AddUint8(0x0e)
}
o := s
for o.Outer != nil {
o = o.Outer
}
if o.Sect == nil {
Errorf(s, "missing section for symbol")
symtab.AddUint8(0)
} else {
symtab.AddUint8(uint8(o.Sect.Extnum))
}
symtab.AddUint16(ctxt.Arch, 0) // desc
symtab.AddUintXX(ctxt.Arch, uint64(Symaddr(s)), ctxt.Arch.PtrSize)
}
}
}
func machodysymtab(ctxt *Link) {
ml := newMachoLoad(ctxt.Arch, LC_DYSYMTAB, 18)
n := 0
ml.data[0] = uint32(n) /* ilocalsym */
ml.data[1] = uint32(nkind[SymKindLocal]) /* nlocalsym */
n += nkind[SymKindLocal]
ml.data[2] = uint32(n) /* iextdefsym */
ml.data[3] = uint32(nkind[SymKindExtdef]) /* nextdefsym */
n += nkind[SymKindExtdef]
ml.data[4] = uint32(n) /* iundefsym */
ml.data[5] = uint32(nkind[SymKindUndef]) /* nundefsym */
ml.data[6] = 0 /* tocoffset */
ml.data[7] = 0 /* ntoc */
ml.data[8] = 0 /* modtaboff */
ml.data[9] = 0 /* nmodtab */
ml.data[10] = 0 /* extrefsymoff */
ml.data[11] = 0 /* nextrefsyms */
// must match domacholink below
s1 := ctxt.Syms.Lookup(".machosymtab", 0)
s2 := ctxt.Syms.Lookup(".linkedit.plt", 0)
s3 := ctxt.Syms.Lookup(".linkedit.got", 0)
ml.data[12] = uint32(linkoff + s1.Size) /* indirectsymoff */
ml.data[13] = uint32((s2.Size + s3.Size) / 4) /* nindirectsyms */
ml.data[14] = 0 /* extreloff */
ml.data[15] = 0 /* nextrel */
ml.data[16] = 0 /* locreloff */
ml.data[17] = 0 /* nlocrel */
}
func Domacholink(ctxt *Link) int64 {
machosymtab(ctxt)
// write data that will be linkedit section
s1 := ctxt.Syms.Lookup(".machosymtab", 0)
s2 := ctxt.Syms.Lookup(".linkedit.plt", 0)
s3 := ctxt.Syms.Lookup(".linkedit.got", 0)
s4 := ctxt.Syms.Lookup(".machosymstr", 0)
// Force the linkedit section to end on a 16-byte
// boundary. This allows pure (non-cgo) Go binaries
// to be code signed correctly.
//
// Apple's codesign_allocate (a helper utility for
// the codesign utility) can do this fine itself if
// it is run on a dynamic Mach-O binary. However,
// when it is run on a pure (non-cgo) Go binary, where
// the linkedit section is mostly empty, it fails to
// account for the extra padding that it itself adds
// when adding the LC_CODE_SIGNATURE load command
// (which must be aligned on a 16-byte boundary).
//
// By forcing the linkedit section to end on a 16-byte
// boundary, codesign_allocate will not need to apply
// any alignment padding itself, working around the
// issue.
for s4.Size%16 != 0 {
s4.AddUint8(0)
}
size := int(s1.Size + s2.Size + s3.Size + s4.Size)
if size > 0 {
linkoff = Rnd(int64(uint64(HEADR)+Segtext.Length), int64(*FlagRound)) + Rnd(int64(Segdata.Filelen), int64(*FlagRound)) + Rnd(int64(Segdwarf.Filelen), int64(*FlagRound))
ctxt.Out.SeekSet(linkoff)
ctxt.Out.Write(s1.P[:s1.Size])
ctxt.Out.Write(s2.P[:s2.Size])
ctxt.Out.Write(s3.P[:s3.Size])
ctxt.Out.Write(s4.P[:s4.Size])
}
return Rnd(int64(size), int64(*FlagRound))
}
func machorelocsect(ctxt *Link, sect *sym.Section, syms []*sym.Symbol) {
// If main section has no bits, nothing to relocate.
if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
return
}
sect.Reloff = uint64(ctxt.Out.Offset())
for i, s := range syms {
if !s.Attr.Reachable() {
continue
}
if uint64(s.Value) >= sect.Vaddr {
syms = syms[i:]
break
}
}
eaddr := int32(sect.Vaddr + sect.Length)
for _, s := range syms {
if !s.Attr.Reachable() {
continue
}
if s.Value >= int64(eaddr) {
break
}
for ri := 0; ri < len(s.R); ri++ {
r := &s.R[ri]
if r.Done {
continue
}
if r.Xsym == nil {
Errorf(s, "missing xsym in relocation")
continue
}
if !r.Xsym.Attr.Reachable() {
Errorf(s, "unreachable reloc %d (%s) target %v", r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Xsym.Name)
}
if !Thearch.Machoreloc1(ctxt.Arch, ctxt.Out, s, r, int64(uint64(s.Value+int64(r.Off))-sect.Vaddr)) {
Errorf(s, "unsupported obj reloc %d (%s)/%d to %s", r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Siz, r.Sym.Name)
}
}
}
sect.Rellen = uint64(ctxt.Out.Offset()) - sect.Reloff
}
func Machoemitreloc(ctxt *Link) {
for ctxt.Out.Offset()&7 != 0 {
ctxt.Out.Write8(0)
}
machorelocsect(ctxt, Segtext.Sections[0], ctxt.Textp)
for _, sect := range Segtext.Sections[1:] {
machorelocsect(ctxt, sect, datap)
}
for _, sect := range Segdata.Sections {
machorelocsect(ctxt, sect, datap)
}
for _, sect := range Segdwarf.Sections {
machorelocsect(ctxt, sect, dwarfp)
}
}