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go/src/cmd/link/internal/loadelf/ldelf.go
Mark Ryan 12e5efd710 cmd/link: fix cgo on riscv64 when building with gcc-15 
It's not currently possible to build cgo programs that are partially
compiled with gcc-15 on riscv64 using the internal linker. There are
two reasons for this.

1. When gcc-15 compiles _cgo_export.c, which contains no actual code,
   for a riscv64 target, it emits a label in the .text section called
   .Letext0. This label is referred to by another section, .debug_line,
   and an entry is generated in the symbol table for it. The Go linker
   panics when processing the .Letext0 symbol in _cgo_export.o, as it
   occurs in an empty section.
2. GCC-15 is generating additional debug symbols with the .LVUS
   prefix, e.g., .LVUS33, that need to be ignored.

We fix the issue by removing the check in
cmd/link/internal/loader/loader.go that panics if we encounter a
symbol in an empty section (the comments preceding this check suggest
it's safe to remove it) and by adding .LVUS to the list of symbol
prefixes to ignore.

Fixes #72840

Change-Id: I00658b6bdd01606dde1581b5bc2f42edfc37de82
Reviewed-on: https://go-review.googlesource.com/c/go/+/668276
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
2025-04-30 11:40:17 -07:00

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// 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 loadelf implements an ELF file reader.
package loadelf
import (
"bytes"
"cmd/internal/bio"
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/loader"
"cmd/link/internal/sym"
"debug/elf"
"encoding/binary"
"fmt"
"io"
"log"
"strings"
)
/*
Derived from Plan 9 from User Space's src/libmach/elf.h, elf.c
https://github.com/9fans/plan9port/tree/master/src/libmach/
Copyright © 2004 Russ Cox.
Portions Copyright © 2008-2010 Google Inc.
Portions Copyright © 2010 The Go Authors.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
const (
SHT_ARM_ATTRIBUTES = 0x70000003
)
type ElfSect struct {
name string
nameoff uint32
type_ elf.SectionType
flags elf.SectionFlag
addr uint64
off uint64
size uint64
link uint32
info uint32
align uint64
entsize uint64
base []byte
readOnlyMem bool // Is this section in readonly memory?
sym loader.Sym
}
type ElfObj struct {
f *bio.Reader
base int64 // offset in f where ELF begins
length int64 // length of ELF
is64 int
name string
e binary.ByteOrder
sect []ElfSect
nsect uint
nsymtab int
symtab *ElfSect
symstr *ElfSect
type_ uint32
machine uint32
version uint32
entry uint64
phoff uint64
shoff uint64
flags uint32
ehsize uint32
phentsize uint32
phnum uint32
shentsize uint32
shnum uint32
shstrndx uint32
}
type ElfSym struct {
name string
value uint64
size uint64
bind elf.SymBind
type_ elf.SymType
other uint8
shndx elf.SectionIndex
sym loader.Sym
}
const (
TagFile = 1
TagCPUName = 4
TagCPURawName = 5
TagCompatibility = 32
TagNoDefaults = 64
TagAlsoCompatibleWith = 65
TagABIVFPArgs = 28
)
type elfAttribute struct {
tag uint64
sval string
ival uint64
}
type elfAttributeList struct {
data []byte
err error
}
func (a *elfAttributeList) string() string {
if a.err != nil {
return ""
}
nul := bytes.IndexByte(a.data, 0)
if nul < 0 {
a.err = io.EOF
return ""
}
s := string(a.data[:nul])
a.data = a.data[nul+1:]
return s
}
func (a *elfAttributeList) uleb128() uint64 {
if a.err != nil {
return 0
}
v, size := binary.Uvarint(a.data)
a.data = a.data[size:]
return v
}
// Read an elfAttribute from the list following the rules used on ARM systems.
func (a *elfAttributeList) armAttr() elfAttribute {
attr := elfAttribute{tag: a.uleb128()}
switch {
case attr.tag == TagCompatibility:
attr.ival = a.uleb128()
attr.sval = a.string()
case attr.tag == TagNoDefaults: // Tag_nodefaults has no argument
case attr.tag == TagAlsoCompatibleWith:
// Not really, but we don't actually care about this tag.
attr.sval = a.string()
// Tag with string argument
case attr.tag == TagCPUName || attr.tag == TagCPURawName || (attr.tag >= 32 && attr.tag&1 != 0):
attr.sval = a.string()
default: // Tag with integer argument
attr.ival = a.uleb128()
}
return attr
}
func (a *elfAttributeList) done() bool {
if a.err != nil || len(a.data) == 0 {
return true
}
return false
}
// Look for the attribute that indicates the object uses the hard-float ABI (a
// file-level attribute with tag Tag_VFP_arch and value 1). Unfortunately the
// format used means that we have to parse all of the file-level attributes to
// find the one we are looking for. This format is slightly documented in "ELF
// for the ARM Architecture" but mostly this is derived from reading the source
// to gold and readelf.
func parseArmAttributes(e binary.ByteOrder, data []byte) (found bool, ehdrFlags uint32, err error) {
found = false
if data[0] != 'A' {
return false, 0, fmt.Errorf(".ARM.attributes has unexpected format %c\n", data[0])
}
data = data[1:]
for len(data) != 0 {
sectionlength := e.Uint32(data)
sectiondata := data[4:sectionlength]
data = data[sectionlength:]
nulIndex := bytes.IndexByte(sectiondata, 0)
if nulIndex < 0 {
return false, 0, fmt.Errorf("corrupt .ARM.attributes (section name not NUL-terminated)\n")
}
name := string(sectiondata[:nulIndex])
sectiondata = sectiondata[nulIndex+1:]
if name != "aeabi" {
continue
}
for len(sectiondata) != 0 {
subsectiontag, sz := binary.Uvarint(sectiondata)
subsectionsize := e.Uint32(sectiondata[sz:])
subsectiondata := sectiondata[sz+4 : subsectionsize]
sectiondata = sectiondata[subsectionsize:]
if subsectiontag != TagFile {
continue
}
attrList := elfAttributeList{data: subsectiondata}
for !attrList.done() {
attr := attrList.armAttr()
if attr.tag == TagABIVFPArgs && attr.ival == 1 {
found = true
ehdrFlags = 0x5000402 // has entry point, Version5 EABI, hard-float ABI
}
}
if attrList.err != nil {
return false, 0, fmt.Errorf("could not parse .ARM.attributes\n")
}
}
}
return found, ehdrFlags, nil
}
// Load loads the ELF file pn from f.
// Symbols are installed into the loader, and a slice of the text symbols is returned.
//
// On ARM systems, Load will attempt to determine what ELF header flags to
// emit by scanning the attributes in the ELF file being loaded. The
// parameter initEhdrFlags contains the current header flags for the output
// object, and the returned ehdrFlags contains what this Load function computes.
// TODO: find a better place for this logic.
func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader, pkg string, length int64, pn string, initEhdrFlags uint32) (textp []loader.Sym, ehdrFlags uint32, err error) {
errorf := func(str string, args ...interface{}) ([]loader.Sym, uint32, error) {
return nil, 0, fmt.Errorf("loadelf: %s: %v", pn, fmt.Sprintf(str, args...))
}
ehdrFlags = initEhdrFlags
base := f.Offset()
var hdrbuf [64]byte
if _, err := io.ReadFull(f, hdrbuf[:]); err != nil {
return errorf("malformed elf file: %v", err)
}
var e binary.ByteOrder
switch elf.Data(hdrbuf[elf.EI_DATA]) {
case elf.ELFDATA2LSB:
e = binary.LittleEndian
case elf.ELFDATA2MSB:
e = binary.BigEndian
default:
return errorf("malformed elf file, unknown header")
}
hdr := new(elf.Header32)
binary.Read(bytes.NewReader(hdrbuf[:]), e, hdr)
if string(hdr.Ident[:elf.EI_CLASS]) != elf.ELFMAG {
return errorf("malformed elf file, bad header")
}
// read header
elfobj := new(ElfObj)
elfobj.e = e
elfobj.f = f
elfobj.base = base
elfobj.length = length
elfobj.name = pn
is64 := 0
class := elf.Class(hdrbuf[elf.EI_CLASS])
if class == elf.ELFCLASS64 {
is64 = 1
hdr := new(elf.Header64)
binary.Read(bytes.NewReader(hdrbuf[:]), e, hdr)
elfobj.type_ = uint32(hdr.Type)
elfobj.machine = uint32(hdr.Machine)
elfobj.version = hdr.Version
elfobj.entry = hdr.Entry
elfobj.phoff = hdr.Phoff
elfobj.shoff = hdr.Shoff
elfobj.flags = hdr.Flags
elfobj.ehsize = uint32(hdr.Ehsize)
elfobj.phentsize = uint32(hdr.Phentsize)
elfobj.phnum = uint32(hdr.Phnum)
elfobj.shentsize = uint32(hdr.Shentsize)
elfobj.shnum = uint32(hdr.Shnum)
elfobj.shstrndx = uint32(hdr.Shstrndx)
} else {
elfobj.type_ = uint32(hdr.Type)
elfobj.machine = uint32(hdr.Machine)
elfobj.version = hdr.Version
elfobj.entry = uint64(hdr.Entry)
elfobj.phoff = uint64(hdr.Phoff)
elfobj.shoff = uint64(hdr.Shoff)
elfobj.flags = hdr.Flags
elfobj.ehsize = uint32(hdr.Ehsize)
elfobj.phentsize = uint32(hdr.Phentsize)
elfobj.phnum = uint32(hdr.Phnum)
elfobj.shentsize = uint32(hdr.Shentsize)
elfobj.shnum = uint32(hdr.Shnum)
elfobj.shstrndx = uint32(hdr.Shstrndx)
}
elfobj.is64 = is64
if v := uint32(hdrbuf[elf.EI_VERSION]); v != elfobj.version {
return errorf("malformed elf version: got %d, want %d", v, elfobj.version)
}
if elf.Type(elfobj.type_) != elf.ET_REL {
return errorf("elf but not elf relocatable object")
}
mach := elf.Machine(elfobj.machine)
switch arch.Family {
default:
return errorf("elf %s unimplemented", arch.Name)
case sys.MIPS:
if mach != elf.EM_MIPS || class != elf.ELFCLASS32 {
return errorf("elf object but not mips")
}
case sys.MIPS64:
if mach != elf.EM_MIPS || class != elf.ELFCLASS64 {
return errorf("elf object but not mips64")
}
case sys.Loong64:
if mach != elf.EM_LOONGARCH || class != elf.ELFCLASS64 {
return errorf("elf object but not loong64")
}
case sys.ARM:
if e != binary.LittleEndian || mach != elf.EM_ARM || class != elf.ELFCLASS32 {
return errorf("elf object but not arm")
}
case sys.AMD64:
if e != binary.LittleEndian || mach != elf.EM_X86_64 || class != elf.ELFCLASS64 {
return errorf("elf object but not amd64")
}
case sys.ARM64:
if e != binary.LittleEndian || mach != elf.EM_AARCH64 || class != elf.ELFCLASS64 {
return errorf("elf object but not arm64")
}
case sys.I386:
if e != binary.LittleEndian || mach != elf.EM_386 || class != elf.ELFCLASS32 {
return errorf("elf object but not 386")
}
case sys.PPC64:
if mach != elf.EM_PPC64 || class != elf.ELFCLASS64 {
return errorf("elf object but not ppc64")
}
case sys.RISCV64:
if mach != elf.EM_RISCV || class != elf.ELFCLASS64 {
return errorf("elf object but not riscv64")
}
case sys.S390X:
if mach != elf.EM_S390 || class != elf.ELFCLASS64 {
return errorf("elf object but not s390x")
}
}
// load section list into memory.
elfobj.sect = make([]ElfSect, elfobj.shnum)
elfobj.nsect = uint(elfobj.shnum)
for i := 0; uint(i) < elfobj.nsect; i++ {
f.MustSeek(int64(uint64(base)+elfobj.shoff+uint64(int64(i)*int64(elfobj.shentsize))), 0)
sect := &elfobj.sect[i]
if is64 != 0 {
var b elf.Section64
if err := binary.Read(f, e, &b); err != nil {
return errorf("malformed elf file: %v", err)
}
sect.nameoff = b.Name
sect.type_ = elf.SectionType(b.Type)
sect.flags = elf.SectionFlag(b.Flags)
sect.addr = b.Addr
sect.off = b.Off
sect.size = b.Size
sect.link = b.Link
sect.info = b.Info
sect.align = b.Addralign
sect.entsize = b.Entsize
} else {
var b elf.Section32
if err := binary.Read(f, e, &b); err != nil {
return errorf("malformed elf file: %v", err)
}
sect.nameoff = b.Name
sect.type_ = elf.SectionType(b.Type)
sect.flags = elf.SectionFlag(b.Flags)
sect.addr = uint64(b.Addr)
sect.off = uint64(b.Off)
sect.size = uint64(b.Size)
sect.link = b.Link
sect.info = b.Info
sect.align = uint64(b.Addralign)
sect.entsize = uint64(b.Entsize)
}
}
// read section string table and translate names
if elfobj.shstrndx >= uint32(elfobj.nsect) {
return errorf("malformed elf file: shstrndx out of range %d >= %d", elfobj.shstrndx, elfobj.nsect)
}
sect := &elfobj.sect[elfobj.shstrndx]
if err := elfmap(elfobj, sect); err != nil {
return errorf("malformed elf file: %v", err)
}
for i := 0; uint(i) < elfobj.nsect; i++ {
if elfobj.sect[i].nameoff != 0 {
elfobj.sect[i].name = cstring(sect.base[elfobj.sect[i].nameoff:])
}
}
// load string table for symbols into memory.
elfobj.symtab = section(elfobj, ".symtab")
if elfobj.symtab == nil {
// our work is done here - no symbols means nothing can refer to this file
return
}
if elfobj.symtab.link <= 0 || elfobj.symtab.link >= uint32(elfobj.nsect) {
return errorf("elf object has symbol table with invalid string table link")
}
elfobj.symstr = &elfobj.sect[elfobj.symtab.link]
if is64 != 0 {
elfobj.nsymtab = int(elfobj.symtab.size / elf.Sym64Size)
} else {
elfobj.nsymtab = int(elfobj.symtab.size / elf.Sym32Size)
}
if err := elfmap(elfobj, elfobj.symtab); err != nil {
return errorf("malformed elf file: %v", err)
}
if err := elfmap(elfobj, elfobj.symstr); err != nil {
return errorf("malformed elf file: %v", err)
}
// load text and data segments into memory.
// they are not as small as the section lists, but we'll need
// the memory anyway for the symbol images, so we might
// as well use one large chunk.
// create symbols for elfmapped sections
sectsymNames := make(map[string]bool)
counter := 0
for i := 0; uint(i) < elfobj.nsect; i++ {
sect = &elfobj.sect[i]
if sect.type_ == SHT_ARM_ATTRIBUTES && sect.name == ".ARM.attributes" {
if err := elfmap(elfobj, sect); err != nil {
return errorf("%s: malformed elf file: %v", pn, err)
}
// We assume the soft-float ABI unless we see a tag indicating otherwise.
if initEhdrFlags == 0x5000002 {
ehdrFlags = 0x5000202
} else {
ehdrFlags = initEhdrFlags
}
found, newEhdrFlags, err := parseArmAttributes(e, sect.base[:sect.size])
if err != nil {
// TODO(dfc) should this return an error?
log.Printf("%s: %v", pn, err)
}
if found {
ehdrFlags = newEhdrFlags
}
}
if (sect.type_ != elf.SHT_PROGBITS && sect.type_ != elf.SHT_NOBITS) || sect.flags&elf.SHF_ALLOC == 0 {
continue
}
if sect.type_ != elf.SHT_NOBITS {
if err := elfmap(elfobj, sect); err != nil {
return errorf("%s: malformed elf file: %v", pn, err)
}
}
name := fmt.Sprintf("%s(%s)", pkg, sect.name)
for sectsymNames[name] {
counter++
name = fmt.Sprintf("%s(%s%d)", pkg, sect.name, counter)
}
sectsymNames[name] = true
sb := l.MakeSymbolUpdater(l.LookupOrCreateCgoExport(name, localSymVersion))
switch sect.flags & (elf.SHF_ALLOC | elf.SHF_WRITE | elf.SHF_EXECINSTR) {
default:
return errorf("%s: unexpected flags for ELF section %s", pn, sect.name)
case elf.SHF_ALLOC:
sb.SetType(sym.SRODATA)
case elf.SHF_ALLOC + elf.SHF_WRITE:
if sect.type_ == elf.SHT_NOBITS {
sb.SetType(sym.SNOPTRBSS)
} else {
sb.SetType(sym.SNOPTRDATA)
}
case elf.SHF_ALLOC + elf.SHF_EXECINSTR:
sb.SetType(sym.STEXT)
}
if sect.name == ".got" || sect.name == ".toc" {
sb.SetType(sym.SELFGOT)
}
if sect.type_ == elf.SHT_PROGBITS {
sb.SetData(sect.base[:sect.size])
sb.SetExternal(true)
}
sb.SetSize(int64(sect.size))
sb.SetAlign(int32(sect.align))
sb.SetReadOnly(sect.readOnlyMem)
sect.sym = sb.Sym()
}
// enter sub-symbols into symbol table.
// symbol 0 is the null symbol.
symbols := make([]loader.Sym, elfobj.nsymtab)
for i := 1; i < elfobj.nsymtab; i++ {
var elfsym ElfSym
if err := readelfsym(l, arch, elfobj, i, &elfsym, 1, localSymVersion); err != nil {
return errorf("%s: malformed elf file: %v", pn, err)
}
symbols[i] = elfsym.sym
if elfsym.type_ != elf.STT_FUNC && elfsym.type_ != elf.STT_OBJECT && elfsym.type_ != elf.STT_NOTYPE && elfsym.type_ != elf.STT_COMMON {
continue
}
if elfsym.shndx == elf.SHN_COMMON || elfsym.type_ == elf.STT_COMMON {
sb := l.MakeSymbolUpdater(elfsym.sym)
if uint64(sb.Size()) < elfsym.size {
sb.SetSize(int64(elfsym.size))
}
if sb.Type() == 0 || sb.Type() == sym.SXREF {
sb.SetType(sym.SNOPTRBSS)
}
continue
}
if uint(elfsym.shndx) >= elfobj.nsect || elfsym.shndx == 0 {
continue
}
// even when we pass needSym == 1 to readelfsym, it might still return nil to skip some unwanted symbols
if elfsym.sym == 0 {
continue
}
sect = &elfobj.sect[elfsym.shndx]
if sect.sym == 0 {
if elfsym.type_ == 0 {
if strings.HasPrefix(sect.name, ".debug_") && elfsym.name == "" {
// clang on arm and riscv64.
// This reportedly happens with clang 3.7 on ARM.
// See issue 13139.
continue
}
if strings.HasPrefix(elfsym.name, ".Ldebug_") || elfsym.name == ".L0 " {
// gcc on riscv64.
continue
}
if elfsym.name == ".Lline_table_start0" {
// clang on riscv64.
continue
}
if strings.HasPrefix(elfsym.name, "$d") && sect.name == ".debug_frame" {
// "$d" is a marker, not a real symbol.
// This happens with gcc on ARM64.
// See https://sourceware.org/bugzilla/show_bug.cgi?id=21809
continue
}
}
if strings.HasPrefix(elfsym.name, ".Linfo_string") {
// clang does this
continue
}
if strings.HasPrefix(elfsym.name, ".LASF") || strings.HasPrefix(elfsym.name, ".LLRL") || strings.HasPrefix(elfsym.name, ".LLST") || strings.HasPrefix(elfsym.name, ".LVUS") {
// gcc on s390x and riscv64 does this.
continue
}
return errorf("%v: sym#%d (%q): ignoring symbol in section %d (%q) (type %d)", elfsym.sym, i, elfsym.name, elfsym.shndx, sect.name, elfsym.type_)
}
s := elfsym.sym
if l.OuterSym(s) != 0 {
if l.AttrDuplicateOK(s) {
continue
}
return errorf("duplicate symbol reference: %s in both %s and %s",
l.SymName(s), l.SymName(l.OuterSym(s)), l.SymName(sect.sym))
}
sectsb := l.MakeSymbolUpdater(sect.sym)
sb := l.MakeSymbolUpdater(s)
sb.SetType(sectsb.Type())
sectsb.AddInteriorSym(s)
if !l.AttrCgoExportDynamic(s) {
sb.SetDynimplib("") // satisfy dynimport
}
sb.SetValue(int64(elfsym.value))
sb.SetSize(int64(elfsym.size))
if sectsb.Type().IsText() {
if l.AttrExternal(s) && !l.AttrDuplicateOK(s) {
return errorf("%s: duplicate symbol definition", sb.Name())
}
l.SetAttrExternal(s, true)
}
if elf.Machine(elfobj.machine) == elf.EM_PPC64 {
flag := int(elfsym.other) >> 5
switch flag {
case 0:
// No local entry. R2 is preserved.
case 1:
// This is kind of a hack, but pass the hint about this symbol's
// usage of R2 (R2 is a caller-save register not a TOC pointer, and
// this function does not have a distinct local entry) by setting
// its SymLocalentry to 1.
l.SetSymLocalentry(s, 1)
case 7:
return errorf("%s: invalid sym.other 0x%x", sb.Name(), elfsym.other)
default:
// Convert the word sized offset into bytes.
l.SetSymLocalentry(s, 4<<uint(flag-2))
}
}
}
// Sort outer lists by address, adding to textp.
// This keeps textp in increasing address order.
for i := uint(0); i < elfobj.nsect; i++ {
s := elfobj.sect[i].sym
if s == 0 {
continue
}
sb := l.MakeSymbolUpdater(s)
if l.SubSym(s) != 0 {
sb.SortSub()
}
if sb.Type().IsText() {
if l.AttrOnList(s) {
return errorf("symbol %s listed multiple times",
l.SymName(s))
}
l.SetAttrOnList(s, true)
textp = append(textp, s)
for ss := l.SubSym(s); ss != 0; ss = l.SubSym(ss) {
if l.AttrOnList(ss) {
return errorf("symbol %s listed multiple times",
l.SymName(ss))
}
l.SetAttrOnList(ss, true)
textp = append(textp, ss)
}
}
}
// load relocations
for i := uint(0); i < elfobj.nsect; i++ {
rsect := &elfobj.sect[i]
if rsect.type_ != elf.SHT_RELA && rsect.type_ != elf.SHT_REL {
continue
}
if rsect.info >= uint32(elfobj.nsect) || elfobj.sect[rsect.info].base == nil {
continue
}
sect = &elfobj.sect[rsect.info]
if err := elfmap(elfobj, rsect); err != nil {
return errorf("malformed elf file: %v", err)
}
rela := 0
if rsect.type_ == elf.SHT_RELA {
rela = 1
}
n := int(rsect.size / uint64(4+4*is64) / uint64(2+rela))
p := rsect.base
sb := l.MakeSymbolUpdater(sect.sym)
for j := 0; j < n; j++ {
var add uint64
var symIdx int
var relocType uint64
var rOff int32
var rAdd int64
var rSym loader.Sym
if is64 != 0 {
// 64-bit rel/rela
rOff = int32(e.Uint64(p))
p = p[8:]
switch arch.Family {
case sys.MIPS64:
// https://www.linux-mips.org/pub/linux/mips/doc/ABI/elf64-2.4.pdf
// The doc shows it's different with general Linux ELF
symIdx = int(e.Uint32(p))
relocType = uint64(p[7])
default:
info := e.Uint64(p)
relocType = info & 0xffffffff
symIdx = int(info >> 32)
}
p = p[8:]
if rela != 0 {
add = e.Uint64(p)
p = p[8:]
}
} else {
// 32-bit rel/rela
rOff = int32(e.Uint32(p))
p = p[4:]
info := e.Uint32(p)
relocType = uint64(info & 0xff)
symIdx = int(info >> 8)
p = p[4:]
if rela != 0 {
add = uint64(e.Uint32(p))
p = p[4:]
}
}
if relocType == 0 { // skip R_*_NONE relocation
j--
n--
continue
}
if symIdx == 0 { // absolute relocation, don't bother reading the null symbol
rSym = 0
} else {
var elfsym ElfSym
if err := readelfsym(l, arch, elfobj, int(symIdx), &elfsym, 0, 0); err != nil {
return errorf("malformed elf file: %v", err)
}
elfsym.sym = symbols[symIdx]
if elfsym.sym == 0 {
return errorf("malformed elf file: %s#%d: reloc of invalid sym #%d %s shndx=%d type=%d", l.SymName(sect.sym), j, int(symIdx), elfsym.name, elfsym.shndx, elfsym.type_)
}
rSym = elfsym.sym
}
rType := objabi.ElfRelocOffset + objabi.RelocType(relocType)
rSize, addendSize, err := relSize(arch, pn, uint32(relocType))
if err != nil {
return nil, 0, err
}
if rela != 0 {
rAdd = int64(add)
} else {
// load addend from image
if rSize == 4 {
rAdd = int64(e.Uint32(sect.base[rOff:]))
} else if rSize == 8 {
rAdd = int64(e.Uint64(sect.base[rOff:]))
} else {
return errorf("invalid rela size %d", rSize)
}
}
if addendSize == 2 {
rAdd = int64(int16(rAdd))
}
if addendSize == 4 {
rAdd = int64(int32(rAdd))
}
r, _ := sb.AddRel(rType)
r.SetOff(rOff)
r.SetSiz(rSize)
r.SetSym(rSym)
r.SetAdd(rAdd)
}
sb.SortRelocs() // just in case
}
return textp, ehdrFlags, nil
}
func section(elfobj *ElfObj, name string) *ElfSect {
for i := 0; uint(i) < elfobj.nsect; i++ {
if elfobj.sect[i].name != "" && name != "" && elfobj.sect[i].name == name {
return &elfobj.sect[i]
}
}
return nil
}
func elfmap(elfobj *ElfObj, sect *ElfSect) (err error) {
if sect.base != nil {
return nil
}
if sect.off+sect.size > uint64(elfobj.length) {
err = fmt.Errorf("elf section past end of file")
return err
}
elfobj.f.MustSeek(int64(uint64(elfobj.base)+sect.off), 0)
sect.base, sect.readOnlyMem, err = elfobj.f.Slice(uint64(sect.size))
if err != nil {
return fmt.Errorf("short read: %v", err)
}
return nil
}
func readelfsym(l *loader.Loader, arch *sys.Arch, elfobj *ElfObj, i int, elfsym *ElfSym, needSym int, localSymVersion int) (err error) {
if i >= elfobj.nsymtab || i < 0 {
err = fmt.Errorf("invalid elf symbol index")
return err
}
if i == 0 {
return fmt.Errorf("readym: read null symbol!")
}
if elfobj.is64 != 0 {
b := new(elf.Sym64)
binary.Read(bytes.NewReader(elfobj.symtab.base[i*elf.Sym64Size:(i+1)*elf.Sym64Size]), elfobj.e, b)
elfsym.name = cstring(elfobj.symstr.base[b.Name:])
elfsym.value = b.Value
elfsym.size = b.Size
elfsym.shndx = elf.SectionIndex(b.Shndx)
elfsym.bind = elf.ST_BIND(b.Info)
elfsym.type_ = elf.ST_TYPE(b.Info)
elfsym.other = b.Other
} else {
b := new(elf.Sym32)
binary.Read(bytes.NewReader(elfobj.symtab.base[i*elf.Sym32Size:(i+1)*elf.Sym32Size]), elfobj.e, b)
elfsym.name = cstring(elfobj.symstr.base[b.Name:])
elfsym.value = uint64(b.Value)
elfsym.size = uint64(b.Size)
elfsym.shndx = elf.SectionIndex(b.Shndx)
elfsym.bind = elf.ST_BIND(b.Info)
elfsym.type_ = elf.ST_TYPE(b.Info)
elfsym.other = b.Other
}
var s loader.Sym
if elfsym.name == "_GLOBAL_OFFSET_TABLE_" {
elfsym.name = ".got"
}
if elfsym.name == ".TOC." {
// Magic symbol on ppc64. Will be set to this object
// file's .got+0x8000.
elfsym.bind = elf.STB_LOCAL
}
switch elfsym.type_ {
case elf.STT_SECTION:
s = elfobj.sect[elfsym.shndx].sym
case elf.STT_OBJECT, elf.STT_FUNC, elf.STT_NOTYPE, elf.STT_COMMON:
switch elfsym.bind {
case elf.STB_GLOBAL:
if needSym != 0 {
s = l.LookupOrCreateCgoExport(elfsym.name, 0)
// for global scoped hidden symbols we should insert it into
// symbol hash table, but mark them as hidden.
// __i686.get_pc_thunk.bx is allowed to be duplicated, to
// workaround that we set dupok.
// TODO(minux): correctly handle __i686.get_pc_thunk.bx without
// set dupok generally. See https://golang.org/cl/5823055
// comment #5 for details.
if s != 0 && elfsym.other == 2 {
if !l.IsExternal(s) {
l.MakeSymbolUpdater(s)
}
l.SetAttrDuplicateOK(s, true)
l.SetAttrVisibilityHidden(s, true)
}
}
case elf.STB_LOCAL:
if (arch.Family == sys.ARM || arch.Family == sys.ARM64) && (strings.HasPrefix(elfsym.name, "$a") || strings.HasPrefix(elfsym.name, "$d") || strings.HasPrefix(elfsym.name, "$x")) {
// binutils for arm and arm64 generate these mapping
// symbols, ignore these
break
}
if elfsym.name == ".TOC." {
// We need to be able to look this up,
// so put it in the hash table.
if needSym != 0 {
s = l.LookupOrCreateCgoExport(elfsym.name, localSymVersion)
l.SetAttrVisibilityHidden(s, true)
}
break
}
if needSym != 0 {
// local names and hidden global names are unique
// and should only be referenced by their index, not name, so we
// don't bother to add them into the hash table
// FIXME: pass empty string here for name? This would
// reduce mem use, but also (possibly) make it harder
// to debug problems.
s = l.CreateStaticSym(elfsym.name)
l.SetAttrVisibilityHidden(s, true)
}
case elf.STB_WEAK:
if needSym != 0 {
s = l.LookupOrCreateCgoExport(elfsym.name, 0)
if elfsym.other == 2 {
l.SetAttrVisibilityHidden(s, true)
}
// Allow weak symbols to be duplicated when already defined.
if l.OuterSym(s) != 0 {
l.SetAttrDuplicateOK(s, true)
}
}
default:
err = fmt.Errorf("%s: invalid symbol binding %d", elfsym.name, elfsym.bind)
return err
}
}
if s != 0 && l.SymType(s) == 0 && elfsym.type_ != elf.STT_SECTION {
sb := l.MakeSymbolUpdater(s)
sb.SetType(sym.SXREF)
}
elfsym.sym = s
return nil
}
// Return the size of the relocated field, and the size of the addend as the first
// and second values. Note, the addend may be larger than the relocation field in
// some cases when a relocated value is split across multiple relocations.
func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, uint8, error) {
// TODO(mdempsky): Replace this with a struct-valued switch statement
// once golang.org/issue/15164 is fixed or found to not impair cmd/link
// performance.
const (
AMD64 = uint32(sys.AMD64)
ARM = uint32(sys.ARM)
ARM64 = uint32(sys.ARM64)
I386 = uint32(sys.I386)
LOONG64 = uint32(sys.Loong64)
MIPS = uint32(sys.MIPS)
MIPS64 = uint32(sys.MIPS64)
PPC64 = uint32(sys.PPC64)
RISCV64 = uint32(sys.RISCV64)
S390X = uint32(sys.S390X)
)
switch uint32(arch.Family) | elftype<<16 {
default:
return 0, 0, fmt.Errorf("%s: unknown relocation type %d; compiled without -fpic?", pn, elftype)
case MIPS | uint32(elf.R_MIPS_HI16)<<16,
MIPS | uint32(elf.R_MIPS_LO16)<<16,
MIPS | uint32(elf.R_MIPS_GOT16)<<16,
MIPS | uint32(elf.R_MIPS_GOT_HI16)<<16,
MIPS | uint32(elf.R_MIPS_GOT_LO16)<<16,
MIPS | uint32(elf.R_MIPS_GPREL16)<<16,
MIPS | uint32(elf.R_MIPS_GOT_PAGE)<<16,
MIPS | uint32(elf.R_MIPS_JALR)<<16,
MIPS | uint32(elf.R_MIPS_GOT_OFST)<<16,
MIPS64 | uint32(elf.R_MIPS_HI16)<<16,
MIPS64 | uint32(elf.R_MIPS_LO16)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT16)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT_HI16)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT_LO16)<<16,
MIPS64 | uint32(elf.R_MIPS_GPREL16)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT_PAGE)<<16,
MIPS64 | uint32(elf.R_MIPS_JALR)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT_OFST)<<16,
MIPS64 | uint32(elf.R_MIPS_CALL16)<<16,
MIPS64 | uint32(elf.R_MIPS_GPREL32)<<16,
MIPS64 | uint32(elf.R_MIPS_64)<<16,
MIPS64 | uint32(elf.R_MIPS_GOT_DISP)<<16,
MIPS64 | uint32(elf.R_MIPS_PC32)<<16:
return 4, 4, nil
case LOONG64 | uint32(elf.R_LARCH_ADD8)<<16,
LOONG64 | uint32(elf.R_LARCH_SUB8)<<16:
return 1, 1, nil
case LOONG64 | uint32(elf.R_LARCH_ADD16)<<16,
LOONG64 | uint32(elf.R_LARCH_SUB16)<<16:
return 2, 2, nil
case LOONG64 | uint32(elf.R_LARCH_MARK_LA)<<16,
LOONG64 | uint32(elf.R_LARCH_MARK_PCREL)<<16,
LOONG64 | uint32(elf.R_LARCH_ADD24)<<16,
LOONG64 | uint32(elf.R_LARCH_ADD32)<<16,
LOONG64 | uint32(elf.R_LARCH_SUB24)<<16,
LOONG64 | uint32(elf.R_LARCH_SUB32)<<16,
LOONG64 | uint32(elf.R_LARCH_B26)<<16,
LOONG64 | uint32(elf.R_LARCH_32_PCREL)<<16:
return 4, 4, nil
case LOONG64 | uint32(elf.R_LARCH_64)<<16,
LOONG64 | uint32(elf.R_LARCH_ADD64)<<16,
LOONG64 | uint32(elf.R_LARCH_SUB64)<<16,
LOONG64 | uint32(elf.R_LARCH_64_PCREL)<<16:
return 8, 8, nil
case S390X | uint32(elf.R_390_8)<<16:
return 1, 1, nil
case PPC64 | uint32(elf.R_PPC64_TOC16)<<16,
S390X | uint32(elf.R_390_16)<<16,
S390X | uint32(elf.R_390_GOT16)<<16,
S390X | uint32(elf.R_390_PC16)<<16,
S390X | uint32(elf.R_390_PC16DBL)<<16,
S390X | uint32(elf.R_390_PLT16DBL)<<16:
return 2, 2, nil
case ARM | uint32(elf.R_ARM_ABS32)<<16,
ARM | uint32(elf.R_ARM_GOT32)<<16,
ARM | uint32(elf.R_ARM_PLT32)<<16,
ARM | uint32(elf.R_ARM_GOTOFF)<<16,
ARM | uint32(elf.R_ARM_GOTPC)<<16,
ARM | uint32(elf.R_ARM_THM_PC22)<<16,
ARM | uint32(elf.R_ARM_REL32)<<16,
ARM | uint32(elf.R_ARM_CALL)<<16,
ARM | uint32(elf.R_ARM_V4BX)<<16,
ARM | uint32(elf.R_ARM_GOT_PREL)<<16,
ARM | uint32(elf.R_ARM_PC24)<<16,
ARM | uint32(elf.R_ARM_JUMP24)<<16,
ARM64 | uint32(elf.R_AARCH64_CALL26)<<16,
ARM64 | uint32(elf.R_AARCH64_ADR_GOT_PAGE)<<16,
ARM64 | uint32(elf.R_AARCH64_LD64_GOT_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_ADR_PREL_PG_HI21)<<16,
ARM64 | uint32(elf.R_AARCH64_ADD_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_LDST8_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_LDST16_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_LDST32_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_LDST64_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_LDST128_ABS_LO12_NC)<<16,
ARM64 | uint32(elf.R_AARCH64_PREL32)<<16,
ARM64 | uint32(elf.R_AARCH64_JUMP26)<<16,
AMD64 | uint32(elf.R_X86_64_PC32)<<16,
AMD64 | uint32(elf.R_X86_64_PLT32)<<16,
AMD64 | uint32(elf.R_X86_64_GOTPCREL)<<16,
AMD64 | uint32(elf.R_X86_64_GOTPCRELX)<<16,
AMD64 | uint32(elf.R_X86_64_REX_GOTPCRELX)<<16,
I386 | uint32(elf.R_386_32)<<16,
I386 | uint32(elf.R_386_PC32)<<16,
I386 | uint32(elf.R_386_GOT32)<<16,
I386 | uint32(elf.R_386_PLT32)<<16,
I386 | uint32(elf.R_386_GOTOFF)<<16,
I386 | uint32(elf.R_386_GOTPC)<<16,
I386 | uint32(elf.R_386_GOT32X)<<16,
PPC64 | uint32(elf.R_PPC64_REL24)<<16,
PPC64 | uint32(elf.R_PPC64_REL24_NOTOC)<<16,
PPC64 | uint32(elf.R_PPC64_REL24_P9NOTOC)<<16,
PPC64 | uint32(elf.R_PPC_REL32)<<16,
S390X | uint32(elf.R_390_32)<<16,
S390X | uint32(elf.R_390_PC32)<<16,
S390X | uint32(elf.R_390_GOT32)<<16,
S390X | uint32(elf.R_390_PLT32)<<16,
S390X | uint32(elf.R_390_PC32DBL)<<16,
S390X | uint32(elf.R_390_PLT32DBL)<<16,
S390X | uint32(elf.R_390_GOTPCDBL)<<16,
S390X | uint32(elf.R_390_GOTENT)<<16:
return 4, 4, nil
case AMD64 | uint32(elf.R_X86_64_64)<<16,
AMD64 | uint32(elf.R_X86_64_PC64)<<16,
ARM64 | uint32(elf.R_AARCH64_ABS64)<<16,
ARM64 | uint32(elf.R_AARCH64_PREL64)<<16,
PPC64 | uint32(elf.R_PPC64_ADDR64)<<16,
PPC64 | uint32(elf.R_PPC64_PCREL34)<<16,
PPC64 | uint32(elf.R_PPC64_GOT_PCREL34)<<16,
PPC64 | uint32(elf.R_PPC64_PLT_PCREL34_NOTOC)<<16,
S390X | uint32(elf.R_390_GLOB_DAT)<<16,
S390X | uint32(elf.R_390_RELATIVE)<<16,
S390X | uint32(elf.R_390_GOTOFF)<<16,
S390X | uint32(elf.R_390_GOTPC)<<16,
S390X | uint32(elf.R_390_64)<<16,
S390X | uint32(elf.R_390_PC64)<<16,
S390X | uint32(elf.R_390_GOT64)<<16,
S390X | uint32(elf.R_390_PLT64)<<16:
return 8, 8, nil
case RISCV64 | uint32(elf.R_RISCV_SET6)<<16,
RISCV64 | uint32(elf.R_RISCV_SUB6)<<16,
RISCV64 | uint32(elf.R_RISCV_SET8)<<16,
RISCV64 | uint32(elf.R_RISCV_SUB8)<<16:
return 1, 1, nil
case RISCV64 | uint32(elf.R_RISCV_RVC_BRANCH)<<16,
RISCV64 | uint32(elf.R_RISCV_RVC_JUMP)<<16,
RISCV64 | uint32(elf.R_RISCV_SET16)<<16,
RISCV64 | uint32(elf.R_RISCV_SUB16)<<16:
return 2, 2, nil
case RISCV64 | uint32(elf.R_RISCV_32)<<16,
RISCV64 | uint32(elf.R_RISCV_BRANCH)<<16,
RISCV64 | uint32(elf.R_RISCV_HI20)<<16,
RISCV64 | uint32(elf.R_RISCV_LO12_I)<<16,
RISCV64 | uint32(elf.R_RISCV_LO12_S)<<16,
RISCV64 | uint32(elf.R_RISCV_GOT_HI20)<<16,
RISCV64 | uint32(elf.R_RISCV_PCREL_HI20)<<16,
RISCV64 | uint32(elf.R_RISCV_PCREL_LO12_I)<<16,
RISCV64 | uint32(elf.R_RISCV_PCREL_LO12_S)<<16,
RISCV64 | uint32(elf.R_RISCV_ADD32)<<16,
RISCV64 | uint32(elf.R_RISCV_SET32)<<16,
RISCV64 | uint32(elf.R_RISCV_SUB32)<<16,
RISCV64 | uint32(elf.R_RISCV_32_PCREL)<<16,
RISCV64 | uint32(elf.R_RISCV_RELAX)<<16:
return 4, 4, nil
case RISCV64 | uint32(elf.R_RISCV_64)<<16,
RISCV64 | uint32(elf.R_RISCV_CALL)<<16,
RISCV64 | uint32(elf.R_RISCV_CALL_PLT)<<16:
return 8, 8, nil
case PPC64 | uint32(elf.R_PPC64_TOC16_LO)<<16,
PPC64 | uint32(elf.R_PPC64_TOC16_HI)<<16,
PPC64 | uint32(elf.R_PPC64_TOC16_HA)<<16,
PPC64 | uint32(elf.R_PPC64_TOC16_DS)<<16,
PPC64 | uint32(elf.R_PPC64_TOC16_LO_DS)<<16,
PPC64 | uint32(elf.R_PPC64_REL16_LO)<<16,
PPC64 | uint32(elf.R_PPC64_REL16_HI)<<16,
PPC64 | uint32(elf.R_PPC64_REL16_HA)<<16,
PPC64 | uint32(elf.R_PPC64_PLT16_HA)<<16,
PPC64 | uint32(elf.R_PPC64_PLT16_LO_DS)<<16:
return 2, 4, nil
// PPC64 inline PLT sequence hint relocations (-fno-plt)
// These are informational annotations to assist linker optimizations.
case PPC64 | uint32(elf.R_PPC64_PLTSEQ)<<16,
PPC64 | uint32(elf.R_PPC64_PLTCALL)<<16,
PPC64 | uint32(elf.R_PPC64_PLTCALL_NOTOC)<<16,
PPC64 | uint32(elf.R_PPC64_PLTSEQ_NOTOC)<<16:
return 0, 0, nil
}
}
func cstring(x []byte) string {
i := bytes.IndexByte(x, '\x00')
if i >= 0 {
x = x[:i]
}
return string(x)
}
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