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Source file src/cmd/link/internal/ld/ldelf.go

Documentation: cmd/link/internal/ld

  package ld
  
  import (
  	"bytes"
  	"cmd/internal/bio"
  	"cmd/internal/objabi"
  	"cmd/internal/sys"
  	"encoding/binary"
  	"fmt"
  	"io"
  	"log"
  	"sort"
  	"strings"
  )
  
  /*
  Derived from Plan 9 from User Space's src/libmach/elf.h, elf.c
  http://code.swtch.com/plan9port/src/tip/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 (
  	ElfClassNone = 0
  	ElfClass32   = 1
  	ElfClass64   = 2
  )
  
  const (
  	ElfDataNone = 0
  	ElfDataLsb  = 1
  	ElfDataMsb  = 2
  )
  
  const (
  	ElfTypeNone         = 0
  	ElfTypeRelocatable  = 1
  	ElfTypeExecutable   = 2
  	ElfTypeSharedObject = 3
  	ElfTypeCore         = 4
  )
  
  const (
  	ElfMachNone        = 0
  	ElfMach32100       = 1
  	ElfMachSparc       = 2
  	ElfMach386         = 3
  	ElfMach68000       = 4
  	ElfMach88000       = 5
  	ElfMach486         = 6
  	ElfMach860         = 7
  	ElfMachMips        = 8
  	ElfMachS370        = 9
  	ElfMachMipsLe      = 10
  	ElfMachParisc      = 15
  	ElfMachVpp500      = 17
  	ElfMachSparc32Plus = 18
  	ElfMach960         = 19
  	ElfMachPower       = 20
  	ElfMachPower64     = 21
  	ElfMachS390        = 22
  	ElfMachV800        = 36
  	ElfMachFr20        = 37
  	ElfMachRh32        = 38
  	ElfMachRce         = 39
  	ElfMachArm         = 40
  	ElfMachAlpha       = 41
  	ElfMachSH          = 42
  	ElfMachSparc9      = 43
  	ElfMachAmd64       = 62
  	ElfMachArm64       = 183
  )
  
  const (
  	ElfAbiNone     = 0
  	ElfAbiSystemV  = 0
  	ElfAbiHPUX     = 1
  	ElfAbiNetBSD   = 2
  	ElfAbiLinux    = 3
  	ElfAbiSolaris  = 6
  	ElfAbiAix      = 7
  	ElfAbiIrix     = 8
  	ElfAbiFreeBSD  = 9
  	ElfAbiTru64    = 10
  	ElfAbiModesto  = 11
  	ElfAbiOpenBSD  = 12
  	ElfAbiARM      = 97
  	ElfAbiEmbedded = 255
  )
  
  const (
  	ElfSectNone      = 0
  	ElfSectProgbits  = 1
  	ElfSectSymtab    = 2
  	ElfSectStrtab    = 3
  	ElfSectRela      = 4
  	ElfSectHash      = 5
  	ElfSectDynamic   = 6
  	ElfSectNote      = 7
  	ElfSectNobits    = 8
  	ElfSectRel       = 9
  	ElfSectShlib     = 10
  	ElfSectDynsym    = 11
  	ElfSectFlagWrite = 0x1
  	ElfSectFlagAlloc = 0x2
  	ElfSectFlagExec  = 0x4
  )
  
  const (
  	ElfSymBindLocal  = 0
  	ElfSymBindGlobal = 1
  	ElfSymBindWeak   = 2
  )
  
  const (
  	ElfSymTypeNone    = 0
  	ElfSymTypeObject  = 1
  	ElfSymTypeFunc    = 2
  	ElfSymTypeSection = 3
  	ElfSymTypeFile    = 4
  	ElfSymTypeCommon  = 5
  	ElfSymTypeTLS     = 6
  )
  
  const (
  	ElfSymShnNone   = 0
  	ElfSymShnAbs    = 0xFFF1
  	ElfSymShnCommon = 0xFFF2
  )
  
  const (
  	ElfProgNone      = 0
  	ElfProgLoad      = 1
  	ElfProgDynamic   = 2
  	ElfProgInterp    = 3
  	ElfProgNote      = 4
  	ElfProgShlib     = 5
  	ElfProgPhdr      = 6
  	ElfProgFlagExec  = 0x1
  	ElfProgFlagWrite = 0x2
  	ElfProgFlagRead  = 0x4
  )
  
  const (
  	ElfNotePrStatus     = 1
  	ElfNotePrFpreg      = 2
  	ElfNotePrPsinfo     = 3
  	ElfNotePrTaskstruct = 4
  	ElfNotePrAuxv       = 6
  	ElfNotePrXfpreg     = 0x46e62b7f
  )
  
  type ElfHdrBytes struct {
  	Ident     [16]uint8
  	Type      [2]uint8
  	Machine   [2]uint8
  	Version   [4]uint8
  	Entry     [4]uint8
  	Phoff     [4]uint8
  	Shoff     [4]uint8
  	Flags     [4]uint8
  	Ehsize    [2]uint8
  	Phentsize [2]uint8
  	Phnum     [2]uint8
  	Shentsize [2]uint8
  	Shnum     [2]uint8
  	Shstrndx  [2]uint8
  }
  
  type ElfSectBytes struct {
  	Name    [4]uint8
  	Type    [4]uint8
  	Flags   [4]uint8
  	Addr    [4]uint8
  	Off     [4]uint8
  	Size    [4]uint8
  	Link    [4]uint8
  	Info    [4]uint8
  	Align   [4]uint8
  	Entsize [4]uint8
  }
  
  type ElfProgBytes struct {
  }
  
  type ElfSymBytes struct {
  	Name  [4]uint8
  	Value [4]uint8
  	Size  [4]uint8
  	Info  uint8
  	Other uint8
  	Shndx [2]uint8
  }
  
  type ElfHdrBytes64 struct {
  	Ident     [16]uint8
  	Type      [2]uint8
  	Machine   [2]uint8
  	Version   [4]uint8
  	Entry     [8]uint8
  	Phoff     [8]uint8
  	Shoff     [8]uint8
  	Flags     [4]uint8
  	Ehsize    [2]uint8
  	Phentsize [2]uint8
  	Phnum     [2]uint8
  	Shentsize [2]uint8
  	Shnum     [2]uint8
  	Shstrndx  [2]uint8
  }
  
  type ElfSectBytes64 struct {
  	Name    [4]uint8
  	Type    [4]uint8
  	Flags   [8]uint8
  	Addr    [8]uint8
  	Off     [8]uint8
  	Size    [8]uint8
  	Link    [4]uint8
  	Info    [4]uint8
  	Align   [8]uint8
  	Entsize [8]uint8
  }
  
  type ElfProgBytes64 struct {
  }
  
  type ElfSymBytes64 struct {
  	Name  [4]uint8
  	Info  uint8
  	Other uint8
  	Shndx [2]uint8
  	Value [8]uint8
  	Size  [8]uint8
  }
  
  type ElfSect struct {
  	name    string
  	nameoff uint32
  	type_   uint32
  	flags   uint64
  	addr    uint64
  	off     uint64
  	size    uint64
  	link    uint32
  	info    uint32
  	align   uint64
  	entsize uint64
  	base    []byte
  	sym     *Symbol
  }
  
  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
  	shstrtab  string
  	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  uint8
  	type_ uint8
  	other uint8
  	shndx uint16
  	sym   *Symbol
  }
  
  var ElfMagic = [4]uint8{0x7F, 'E', 'L', 'F'}
  
  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 == 64: // Tag_nodefaults has no argument
  
  	case attr.tag == 65: // Tag_also_compatible_with
  		// 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(ctxt *Link, e binary.ByteOrder, data []byte) {
  	// We assume the soft-float ABI unless we see a tag indicating otherwise.
  	if ehdr.flags == 0x5000002 {
  		ehdr.flags = 0x5000202
  	}
  	if data[0] != 'A' {
  		// TODO(dfc) should this be ctxt.Diag ?
  		ctxt.Logf(".ARM.attributes has unexpected format %c\n", data[0])
  		return
  	}
  	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 {
  			// TODO(dfc) should this be ctxt.Diag ?
  			ctxt.Logf("corrupt .ARM.attributes (section name not NUL-terminated)\n")
  			return
  		}
  		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 {
  				attrList := elfAttributeList{data: subsectiondata}
  				for !attrList.done() {
  					attr := attrList.armAttr()
  					if attr.tag == TagABIVFPArgs && attr.ival == 1 {
  						ehdr.flags = 0x5000402 // has entry point, Version5 EABI, hard-float ABI
  					}
  				}
  				if attrList.err != nil {
  					// TODO(dfc) should this be ctxt.Diag ?
  					ctxt.Logf("could not parse .ARM.attributes\n")
  				}
  			}
  		}
  	}
  }
  
  func ldelf(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f ldelf %s\n", Cputime(), pn)
  	}
  
  	localSymVersion := ctxt.Syms.IncVersion()
  	base := f.Offset()
  
  	var add uint64
  	var e binary.ByteOrder
  	var elfobj *ElfObj
  	var flag int
  	var hdr *ElfHdrBytes
  	var hdrbuf [64]uint8
  	var info uint64
  	var is64 int
  	var j int
  	var n int
  	var name string
  	var p []byte
  	var r []Reloc
  	var rela int
  	var rp *Reloc
  	var rsect *ElfSect
  	var s *Symbol
  	var sect *ElfSect
  	var sym ElfSym
  	var symbols []*Symbol
  	if _, err := io.ReadFull(f, hdrbuf[:]); err != nil {
  		Errorf(nil, "%s: malformed elf file: %v", pn, err)
  		return
  	}
  	hdr = new(ElfHdrBytes)
  	binary.Read(bytes.NewReader(hdrbuf[:]), binary.BigEndian, hdr) // only byte arrays; byte order doesn't matter
  	if string(hdr.Ident[:4]) != "\x7FELF" {
  		Errorf(nil, "%s: malformed elf file", pn)
  		return
  	}
  	switch hdr.Ident[5] {
  	case ElfDataLsb:
  		e = binary.LittleEndian
  
  	case ElfDataMsb:
  		e = binary.BigEndian
  
  	default:
  		Errorf(nil, "%s: malformed elf file", pn)
  		return
  	}
  
  	// read header
  	elfobj = new(ElfObj)
  
  	elfobj.e = e
  	elfobj.f = f
  	elfobj.base = base
  	elfobj.length = length
  	elfobj.name = pn
  
  	is64 = 0
  	if hdr.Ident[4] == ElfClass64 {
  		is64 = 1
  		hdr := new(ElfHdrBytes64)
  		binary.Read(bytes.NewReader(hdrbuf[:]), binary.BigEndian, hdr) // only byte arrays; byte order doesn't matter
  		elfobj.type_ = uint32(e.Uint16(hdr.Type[:]))
  		elfobj.machine = uint32(e.Uint16(hdr.Machine[:]))
  		elfobj.version = e.Uint32(hdr.Version[:])
  		elfobj.phoff = e.Uint64(hdr.Phoff[:])
  		elfobj.shoff = e.Uint64(hdr.Shoff[:])
  		elfobj.flags = e.Uint32(hdr.Flags[:])
  		elfobj.ehsize = uint32(e.Uint16(hdr.Ehsize[:]))
  		elfobj.phentsize = uint32(e.Uint16(hdr.Phentsize[:]))
  		elfobj.phnum = uint32(e.Uint16(hdr.Phnum[:]))
  		elfobj.shentsize = uint32(e.Uint16(hdr.Shentsize[:]))
  		elfobj.shnum = uint32(e.Uint16(hdr.Shnum[:]))
  		elfobj.shstrndx = uint32(e.Uint16(hdr.Shstrndx[:]))
  	} else {
  		elfobj.type_ = uint32(e.Uint16(hdr.Type[:]))
  		elfobj.machine = uint32(e.Uint16(hdr.Machine[:]))
  		elfobj.version = e.Uint32(hdr.Version[:])
  		elfobj.entry = uint64(e.Uint32(hdr.Entry[:]))
  		elfobj.phoff = uint64(e.Uint32(hdr.Phoff[:]))
  		elfobj.shoff = uint64(e.Uint32(hdr.Shoff[:]))
  		elfobj.flags = e.Uint32(hdr.Flags[:])
  		elfobj.ehsize = uint32(e.Uint16(hdr.Ehsize[:]))
  		elfobj.phentsize = uint32(e.Uint16(hdr.Phentsize[:]))
  		elfobj.phnum = uint32(e.Uint16(hdr.Phnum[:]))
  		elfobj.shentsize = uint32(e.Uint16(hdr.Shentsize[:]))
  		elfobj.shnum = uint32(e.Uint16(hdr.Shnum[:]))
  		elfobj.shstrndx = uint32(e.Uint16(hdr.Shstrndx[:]))
  	}
  
  	elfobj.is64 = is64
  
  	if v := uint32(hdr.Ident[6]); v != elfobj.version {
  		Errorf(nil, "%s: malformed elf version: got %d, want %d", pn, v, elfobj.version)
  		return
  	}
  
  	if e.Uint16(hdr.Type[:]) != ElfTypeRelocatable {
  		Errorf(nil, "%s: elf but not elf relocatable object", pn)
  		return
  	}
  
  	switch SysArch.Family {
  	default:
  		Errorf(nil, "%s: elf %s unimplemented", pn, SysArch.Name)
  		return
  
  	case sys.MIPS:
  		if elfobj.machine != ElfMachMips || hdr.Ident[4] != ElfClass32 {
  			Errorf(nil, "%s: elf object but not mips", pn)
  			return
  		}
  
  	case sys.MIPS64:
  		if elfobj.machine != ElfMachMips || hdr.Ident[4] != ElfClass64 {
  			Errorf(nil, "%s: elf object but not mips64", pn)
  			return
  		}
  
  	case sys.ARM:
  		if e != binary.LittleEndian || elfobj.machine != ElfMachArm || hdr.Ident[4] != ElfClass32 {
  			Errorf(nil, "%s: elf object but not arm", pn)
  			return
  		}
  
  	case sys.AMD64:
  		if e != binary.LittleEndian || elfobj.machine != ElfMachAmd64 || hdr.Ident[4] != ElfClass64 {
  			Errorf(nil, "%s: elf object but not amd64", pn)
  			return
  		}
  
  	case sys.ARM64:
  		if e != binary.LittleEndian || elfobj.machine != ElfMachArm64 || hdr.Ident[4] != ElfClass64 {
  			Errorf(nil, "%s: elf object but not arm64", pn)
  			return
  		}
  
  	case sys.I386:
  		if e != binary.LittleEndian || elfobj.machine != ElfMach386 || hdr.Ident[4] != ElfClass32 {
  			Errorf(nil, "%s: elf object but not 386", pn)
  			return
  		}
  
  	case sys.PPC64:
  		if elfobj.machine != ElfMachPower64 || hdr.Ident[4] != ElfClass64 {
  			Errorf(nil, "%s: elf object but not ppc64", pn)
  			return
  		}
  
  	case sys.S390X:
  		if elfobj.machine != ElfMachS390 || hdr.Ident[4] != ElfClass64 {
  			Errorf(nil, "%s: elf object but not s390x", pn)
  			return
  		}
  	}
  
  	// load section list into memory.
  	elfobj.sect = make([]ElfSect, elfobj.shnum)
  
  	elfobj.nsect = uint(elfobj.shnum)
  	for i := 0; uint(i) < elfobj.nsect; i++ {
  		if f.Seek(int64(uint64(base)+elfobj.shoff+uint64(int64(i)*int64(elfobj.shentsize))), 0) < 0 {
  			Errorf(nil, "%s: malformed elf file", pn)
  			return
  		}
  		sect = &elfobj.sect[i]
  		if is64 != 0 {
  			var b ElfSectBytes64
  
  			if err := binary.Read(f, e, &b); err != nil {
  				Errorf(nil, "%s: malformed elf file: %v", pn, err)
  				return
  			}
  
  			sect.nameoff = e.Uint32(b.Name[:])
  			sect.type_ = e.Uint32(b.Type[:])
  			sect.flags = e.Uint64(b.Flags[:])
  			sect.addr = e.Uint64(b.Addr[:])
  			sect.off = e.Uint64(b.Off[:])
  			sect.size = e.Uint64(b.Size[:])
  			sect.link = e.Uint32(b.Link[:])
  			sect.info = e.Uint32(b.Info[:])
  			sect.align = e.Uint64(b.Align[:])
  			sect.entsize = e.Uint64(b.Entsize[:])
  		} else {
  			var b ElfSectBytes
  
  			if err := binary.Read(f, e, &b); err != nil {
  				Errorf(nil, "%s: malformed elf file: %v", pn, err)
  				return
  			}
  
  			sect.nameoff = e.Uint32(b.Name[:])
  			sect.type_ = e.Uint32(b.Type[:])
  			sect.flags = uint64(e.Uint32(b.Flags[:]))
  			sect.addr = uint64(e.Uint32(b.Addr[:]))
  			sect.off = uint64(e.Uint32(b.Off[:]))
  			sect.size = uint64(e.Uint32(b.Size[:]))
  			sect.link = e.Uint32(b.Link[:])
  			sect.info = e.Uint32(b.Info[:])
  			sect.align = uint64(e.Uint32(b.Align[:]))
  			sect.entsize = uint64(e.Uint32(b.Entsize[:]))
  		}
  	}
  
  	// read section string table and translate names
  	if elfobj.shstrndx >= uint32(elfobj.nsect) {
  		Errorf(nil, "%s: malformed elf file: shstrndx out of range %d >= %d", pn, elfobj.shstrndx, elfobj.nsect)
  		return
  	}
  
  	sect = &elfobj.sect[elfobj.shstrndx]
  	if err := elfmap(elfobj, sect); err != nil {
  		Errorf(nil, "%s: malformed elf file: %v", pn, err)
  		return
  	}
  	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) {
  		Errorf(nil, "%s: elf object has symbol table with invalid string table link", pn)
  		return
  	}
  
  	elfobj.symstr = &elfobj.sect[elfobj.symtab.link]
  	if is64 != 0 {
  		elfobj.nsymtab = int(elfobj.symtab.size / ELF64SYMSIZE)
  	} else {
  		elfobj.nsymtab = int(elfobj.symtab.size / ELF32SYMSIZE)
  	}
  
  	if err := elfmap(elfobj, elfobj.symtab); err != nil {
  		Errorf(nil, "%s: malformed elf file: %v", pn, err)
  		return
  	}
  	if err := elfmap(elfobj, elfobj.symstr); err != nil {
  		Errorf(nil, "%s: malformed elf file: %v", pn, err)
  		return
  	}
  
  	// 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
  	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 {
  				Errorf(nil, "%s: malformed elf file: %v", pn, err)
  				return
  			}
  			parseArmAttributes(ctxt, e, sect.base[:sect.size])
  		}
  		if (sect.type_ != ElfSectProgbits && sect.type_ != ElfSectNobits) || sect.flags&ElfSectFlagAlloc == 0 {
  			continue
  		}
  		if sect.type_ != ElfSectNobits {
  			if err := elfmap(elfobj, sect); err != nil {
  				Errorf(nil, "%s: malformed elf file: %v", pn, err)
  				return
  			}
  		}
  
  		name = fmt.Sprintf("%s(%s)", pkg, sect.name)
  		s = ctxt.Syms.Lookup(name, localSymVersion)
  
  		switch int(sect.flags) & (ElfSectFlagAlloc | ElfSectFlagWrite | ElfSectFlagExec) {
  		default:
  			Errorf(nil, "%s: unexpected flags for ELF section %s", pn, sect.name)
  			return
  
  		case ElfSectFlagAlloc:
  			s.Type = SRODATA
  
  		case ElfSectFlagAlloc + ElfSectFlagWrite:
  			if sect.type_ == ElfSectNobits {
  				s.Type = SNOPTRBSS
  			} else {
  				s.Type = SNOPTRDATA
  			}
  
  		case ElfSectFlagAlloc + ElfSectFlagExec:
  			s.Type = STEXT
  		}
  
  		if sect.name == ".got" || sect.name == ".toc" {
  			s.Type = SELFGOT
  		}
  		if sect.type_ == ElfSectProgbits {
  			s.P = sect.base
  			s.P = s.P[:sect.size]
  		}
  
  		s.Size = int64(sect.size)
  		s.Align = int32(sect.align)
  		sect.sym = s
  	}
  
  	// enter sub-symbols into symbol table.
  	// symbol 0 is the null symbol.
  	symbols = make([]*Symbol, elfobj.nsymtab)
  
  	for i := 1; i < elfobj.nsymtab; i++ {
  		if err := readelfsym(ctxt, elfobj, i, &sym, 1, localSymVersion); err != nil {
  			Errorf(nil, "%s: malformed elf file: %v", pn, err)
  			return
  		}
  		symbols[i] = sym.sym
  		if sym.type_ != ElfSymTypeFunc && sym.type_ != ElfSymTypeObject && sym.type_ != ElfSymTypeNone && sym.type_ != ElfSymTypeCommon {
  			continue
  		}
  		if sym.shndx == ElfSymShnCommon || sym.type_ == ElfSymTypeCommon {
  			s = sym.sym
  			if uint64(s.Size) < sym.size {
  				s.Size = int64(sym.size)
  			}
  			if s.Type == 0 || s.Type == SXREF {
  				s.Type = SNOPTRBSS
  			}
  			continue
  		}
  
  		if uint(sym.shndx) >= elfobj.nsect || sym.shndx == 0 {
  			continue
  		}
  
  		// even when we pass needSym == 1 to readelfsym, it might still return nil to skip some unwanted symbols
  		if sym.sym == nil {
  			continue
  		}
  		sect = &elfobj.sect[sym.shndx]
  		if sect.sym == nil {
  			if strings.HasPrefix(sym.name, ".Linfo_string") { // clang does this
  				continue
  			}
  
  			if sym.name == "" && sym.type_ == 0 && sect.name == ".debug_str" {
  				// This reportedly happens with clang 3.7 on ARM.
  				// See issue 13139.
  				continue
  			}
  
  			if strings.HasPrefix(sym.name, ".LASF") { // gcc on s390x does this
  				continue
  			}
  			Errorf(sym.sym, "%s: sym#%d: ignoring symbol in section %d (type %d)", pn, i, sym.shndx, sym.type_)
  			continue
  		}
  
  		s = sym.sym
  		if s.Outer != nil {
  			if s.Attr.DuplicateOK() {
  				continue
  			}
  			Exitf("%s: duplicate symbol reference: %s in both %s and %s", pn, s.Name, s.Outer.Name, sect.sym.Name)
  		}
  
  		s.Sub = sect.sym.Sub
  		sect.sym.Sub = s
  		s.Type = sect.sym.Type | s.Type&^SMASK | SSUB
  		if !s.Attr.CgoExportDynamic() {
  			s.Dynimplib = "" // satisfy dynimport
  		}
  		s.Value = int64(sym.value)
  		s.Size = int64(sym.size)
  		s.Outer = sect.sym
  		if sect.sym.Type == STEXT {
  			if s.Attr.External() && !s.Attr.DuplicateOK() {
  				Errorf(s, "%s: duplicate symbol definition", pn)
  			}
  			s.Attr |= AttrExternal
  		}
  
  		if elfobj.machine == ElfMachPower64 {
  			flag = int(sym.other) >> 5
  			if 2 <= flag && flag <= 6 {
  				s.Localentry = 1 << uint(flag-2)
  			} else if flag == 7 {
  				Errorf(s, "%s: invalid sym.other 0x%x", pn, sym.other)
  			}
  		}
  	}
  
  	// Sort outer lists by address, adding to textp.
  	// This keeps textp in increasing address order.
  	for i := 0; uint(i) < elfobj.nsect; i++ {
  		s = elfobj.sect[i].sym
  		if s == nil {
  			continue
  		}
  		if s.Sub != nil {
  			s.Sub = listsort(s.Sub)
  		}
  		if s.Type == STEXT {
  			if s.Attr.OnList() {
  				log.Fatalf("symbol %s listed multiple times", s.Name)
  			}
  			s.Attr |= AttrOnList
  			ctxt.Textp = append(ctxt.Textp, s)
  			for s = s.Sub; s != nil; s = s.Sub {
  				if s.Attr.OnList() {
  					log.Fatalf("symbol %s listed multiple times", s.Name)
  				}
  				s.Attr |= AttrOnList
  				ctxt.Textp = append(ctxt.Textp, s)
  			}
  		}
  	}
  
  	// load relocations
  	for i := 0; uint(i) < elfobj.nsect; i++ {
  		rsect = &elfobj.sect[i]
  		if rsect.type_ != ElfSectRela && rsect.type_ != ElfSectRel {
  			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 {
  			Errorf(nil, "%s: malformed elf file: %v", pn, err)
  			return
  		}
  		rela = 0
  		if rsect.type_ == ElfSectRela {
  			rela = 1
  		}
  		n = int(rsect.size / uint64(4+4*is64) / uint64(2+rela))
  		r = make([]Reloc, n)
  		p = rsect.base
  		for j = 0; j < n; j++ {
  			add = 0
  			rp = &r[j]
  			if is64 != 0 {
  				// 64-bit rel/rela
  				rp.Off = int32(e.Uint64(p))
  
  				p = p[8:]
  				info = e.Uint64(p)
  				p = p[8:]
  				if rela != 0 {
  					add = e.Uint64(p)
  					p = p[8:]
  				}
  			} else {
  				// 32-bit rel/rela
  				rp.Off = int32(e.Uint32(p))
  
  				p = p[4:]
  				info = uint64(e.Uint32(p))
  				info = info>>8<<32 | info&0xff // convert to 64-bit info
  				p = p[4:]
  				if rela != 0 {
  					add = uint64(e.Uint32(p))
  					p = p[4:]
  				}
  			}
  
  			if info&0xffffffff == 0 { // skip R_*_NONE relocation
  				j--
  				n--
  				continue
  			}
  
  			if info>>32 == 0 { // absolute relocation, don't bother reading the null symbol
  				rp.Sym = nil
  			} else {
  				if err := readelfsym(ctxt, elfobj, int(info>>32), &sym, 0, 0); err != nil {
  					Errorf(nil, "%s: malformed elf file: %v", pn, err)
  					return
  				}
  				sym.sym = symbols[info>>32]
  				if sym.sym == nil {
  					Errorf(nil, "%s: malformed elf file: %s#%d: reloc of invalid sym #%d %s shndx=%d type=%d", pn, sect.sym.Name, j, int(info>>32), sym.name, sym.shndx, sym.type_)
  					return
  				}
  
  				rp.Sym = sym.sym
  			}
  
  			rp.Type = 256 + objabi.RelocType(info)
  			rp.Siz = relSize(ctxt, pn, uint32(info))
  			if rela != 0 {
  				rp.Add = int64(add)
  			} else {
  				// load addend from image
  				if rp.Siz == 4 {
  					rp.Add = int64(e.Uint32(sect.base[rp.Off:]))
  				} else if rp.Siz == 8 {
  					rp.Add = int64(e.Uint64(sect.base[rp.Off:]))
  				} else {
  					Errorf(nil, "invalid rela size %d", rp.Siz)
  				}
  			}
  
  			if rp.Siz == 2 {
  				rp.Add = int64(int16(rp.Add))
  			}
  			if rp.Siz == 4 {
  				rp.Add = int64(int32(rp.Add))
  			}
  		}
  
  		//print("rel %s %d %d %s %#llx\n", sect->sym->name, rp->type, rp->siz, rp->sym->name, rp->add);
  		sort.Sort(rbyoff(r[:n]))
  		// just in case
  
  		s = sect.sym
  		s.R = r
  		s.R = s.R[:n]
  	}
  }
  
  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
  	}
  
  	sect.base = make([]byte, sect.size)
  	if elfobj.f.Seek(int64(uint64(elfobj.base)+sect.off), 0) < 0 {
  		return fmt.Errorf("short read: seek not successful")
  	}
  	if _, err := io.ReadFull(elfobj.f, sect.base); err != nil {
  		return fmt.Errorf("short read: %v", err)
  	}
  
  	return nil
  }
  
  func readelfsym(ctxt *Link, elfobj *ElfObj, i int, sym *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 {
  		Errorf(nil, "readym: read null symbol!")
  	}
  
  	if elfobj.is64 != 0 {
  		b := new(ElfSymBytes64)
  		binary.Read(bytes.NewReader(elfobj.symtab.base[i*ELF64SYMSIZE:(i+1)*ELF64SYMSIZE]), elfobj.e, b)
  		sym.name = cstring(elfobj.symstr.base[elfobj.e.Uint32(b.Name[:]):])
  		sym.value = elfobj.e.Uint64(b.Value[:])
  		sym.size = elfobj.e.Uint64(b.Size[:])
  		sym.shndx = elfobj.e.Uint16(b.Shndx[:])
  		sym.bind = b.Info >> 4
  		sym.type_ = b.Info & 0xf
  		sym.other = b.Other
  	} else {
  		b := new(ElfSymBytes)
  		binary.Read(bytes.NewReader(elfobj.symtab.base[i*ELF32SYMSIZE:(i+1)*ELF32SYMSIZE]), elfobj.e, b)
  		sym.name = cstring(elfobj.symstr.base[elfobj.e.Uint32(b.Name[:]):])
  		sym.value = uint64(elfobj.e.Uint32(b.Value[:]))
  		sym.size = uint64(elfobj.e.Uint32(b.Size[:]))
  		sym.shndx = elfobj.e.Uint16(b.Shndx[:])
  		sym.bind = b.Info >> 4
  		sym.type_ = b.Info & 0xf
  		sym.other = b.Other
  	}
  
  	var s *Symbol
  	if sym.name == "_GLOBAL_OFFSET_TABLE_" {
  		sym.name = ".got"
  	}
  	if sym.name == ".TOC." {
  		// Magic symbol on ppc64.  Will be set to this object
  		// file's .got+0x8000.
  		sym.bind = ElfSymBindLocal
  	}
  
  	switch sym.type_ {
  	case ElfSymTypeSection:
  		s = elfobj.sect[sym.shndx].sym
  
  	case ElfSymTypeObject, ElfSymTypeFunc, ElfSymTypeNone, ElfSymTypeCommon:
  		switch sym.bind {
  		case ElfSymBindGlobal:
  			if needSym != 0 {
  				s = ctxt.Syms.Lookup(sym.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 http://codereview.appspot.com/5823055/
  				// comment #5 for details.
  				if s != nil && sym.other == 2 {
  					s.Type |= SHIDDEN
  					s.Attr |= AttrDuplicateOK
  				}
  			}
  
  		case ElfSymBindLocal:
  			if SysArch.Family == sys.ARM && (strings.HasPrefix(sym.name, "$a") || strings.HasPrefix(sym.name, "$d")) {
  				// binutils for arm generate these mapping
  				// symbols, ignore these
  				break
  			}
  
  			if sym.name == ".TOC." {
  				// We need to be able to look this up,
  				// so put it in the hash table.
  				if needSym != 0 {
  					s = ctxt.Syms.Lookup(sym.name, localSymVersion)
  					s.Type |= SHIDDEN
  				}
  
  				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
  				s = ctxt.Syms.newsym(sym.name, localSymVersion)
  
  				s.Type |= SHIDDEN
  			}
  
  		case ElfSymBindWeak:
  			if needSym != 0 {
  				s = ctxt.Syms.Lookup(sym.name, 0)
  				if sym.other == 2 {
  					s.Type |= SHIDDEN
  				}
  			}
  
  		default:
  			err = fmt.Errorf("%s: invalid symbol binding %d", sym.name, sym.bind)
  			return err
  		}
  	}
  
  	if s != nil && s.Type == 0 && sym.type_ != ElfSymTypeSection {
  		s.Type = SXREF
  	}
  	sym.sym = s
  
  	return nil
  }
  
  type rbyoff []Reloc
  
  func (x rbyoff) Len() int {
  	return len(x)
  }
  
  func (x rbyoff) Swap(i, j int) {
  	x[i], x[j] = x[j], x[i]
  }
  
  func (x rbyoff) Less(i, j int) bool {
  	a := &x[i]
  	b := &x[j]
  	if a.Off < b.Off {
  		return true
  	}
  	if a.Off > b.Off {
  		return false
  	}
  	return false
  }
  
  func relSize(ctxt *Link, pn string, elftype uint32) uint8 {
  	// 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)
  		I386  = uint32(sys.I386)
  		PPC64 = uint32(sys.PPC64)
  		S390X = uint32(sys.S390X)
  	)
  
  	switch uint32(SysArch.Family) | elftype<<24 {
  	default:
  		Errorf(nil, "%s: unknown relocation type %d; compiled without -fpic?", pn, elftype)
  		fallthrough
  
  	case S390X | R_390_8<<24:
  		return 1
  
  	case PPC64 | R_PPC64_TOC16<<24,
  		PPC64 | R_PPC64_TOC16_LO<<24,
  		PPC64 | R_PPC64_TOC16_HI<<24,
  		PPC64 | R_PPC64_TOC16_HA<<24,
  		PPC64 | R_PPC64_TOC16_DS<<24,
  		PPC64 | R_PPC64_TOC16_LO_DS<<24,
  		PPC64 | R_PPC64_REL16_LO<<24,
  		PPC64 | R_PPC64_REL16_HI<<24,
  		PPC64 | R_PPC64_REL16_HA<<24,
  		S390X | R_390_16<<24,
  		S390X | R_390_GOT16<<24,
  		S390X | R_390_PC16<<24,
  		S390X | R_390_PC16DBL<<24,
  		S390X | R_390_PLT16DBL<<24:
  		return 2
  
  	case ARM | R_ARM_ABS32<<24,
  		ARM | R_ARM_GOT32<<24,
  		ARM | R_ARM_PLT32<<24,
  		ARM | R_ARM_GOTOFF<<24,
  		ARM | R_ARM_GOTPC<<24,
  		ARM | R_ARM_THM_PC22<<24,
  		ARM | R_ARM_REL32<<24,
  		ARM | R_ARM_CALL<<24,
  		ARM | R_ARM_V4BX<<24,
  		ARM | R_ARM_GOT_PREL<<24,
  		ARM | R_ARM_PC24<<24,
  		ARM | R_ARM_JUMP24<<24,
  		AMD64 | R_X86_64_PC32<<24,
  		AMD64 | R_X86_64_PLT32<<24,
  		AMD64 | R_X86_64_GOTPCREL<<24,
  		AMD64 | R_X86_64_GOTPCRELX<<24,
  		AMD64 | R_X86_64_REX_GOTPCRELX<<24,
  		I386 | R_386_32<<24,
  		I386 | R_386_PC32<<24,
  		I386 | R_386_GOT32<<24,
  		I386 | R_386_PLT32<<24,
  		I386 | R_386_GOTOFF<<24,
  		I386 | R_386_GOTPC<<24,
  		I386 | R_386_GOT32X<<24,
  		PPC64 | R_PPC64_REL24<<24,
  		PPC64 | R_PPC_REL32<<24,
  		S390X | R_390_32<<24,
  		S390X | R_390_PC32<<24,
  		S390X | R_390_GOT32<<24,
  		S390X | R_390_PLT32<<24,
  		S390X | R_390_PC32DBL<<24,
  		S390X | R_390_PLT32DBL<<24,
  		S390X | R_390_GOTPCDBL<<24,
  		S390X | R_390_GOTENT<<24:
  		return 4
  
  	case AMD64 | R_X86_64_64<<24,
  		PPC64 | R_PPC64_ADDR64<<24,
  		S390X | R_390_GLOB_DAT<<24,
  		S390X | R_390_RELATIVE<<24,
  		S390X | R_390_GOTOFF<<24,
  		S390X | R_390_GOTPC<<24,
  		S390X | R_390_64<<24,
  		S390X | R_390_PC64<<24,
  		S390X | R_390_GOT64<<24,
  		S390X | R_390_PLT64<<24:
  		return 8
  	}
  }
  

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