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// Copyright 2020 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/link/internal/loader"
"cmd/link/internal/sym"
"fmt"
"runtime"
"sync"
)
// Assembling the binary is broken into two steps:
// - writing out the code/data/dwarf Segments, applying relocations on the fly
// - writing out the architecture specific pieces.
// This function handles the first part.
func asmb(ctxt *Link) {
// TODO(jfaller): delete me.
if thearch.Asmb != nil {
thearch.Asmb(ctxt, ctxt.loader)
return
}
if ctxt.IsELF {
Asmbelfsetup()
}
var wg sync.WaitGroup
f := func(ctxt *Link, out *OutBuf, start, length int64) {
pad := thearch.CodePad
if pad == nil {
pad = zeros[:]
}
CodeblkPad(ctxt, out, start, length, pad)
}
for _, sect := range Segtext.Sections {
offset := sect.Vaddr - Segtext.Vaddr + Segtext.Fileoff
// Handle text sections with Codeblk
if sect.Name == ".text" {
writeParallel(&wg, f, ctxt, offset, sect.Vaddr, sect.Length)
} else {
writeParallel(&wg, datblk, ctxt, offset, sect.Vaddr, sect.Length)
}
}
if Segrodata.Filelen > 0 {
writeParallel(&wg, datblk, ctxt, Segrodata.Fileoff, Segrodata.Vaddr, Segrodata.Filelen)
}
if Segrelrodata.Filelen > 0 {
writeParallel(&wg, datblk, ctxt, Segrelrodata.Fileoff, Segrelrodata.Vaddr, Segrelrodata.Filelen)
}
writeParallel(&wg, datblk, ctxt, Segdata.Fileoff, Segdata.Vaddr, Segdata.Filelen)
writeParallel(&wg, dwarfblk, ctxt, Segdwarf.Fileoff, Segdwarf.Vaddr, Segdwarf.Filelen)
wg.Wait()
}
// Assembling the binary is broken into two steps:
// - writing out the code/data/dwarf Segments
// - writing out the architecture specific pieces.
// This function handles the second part.
func asmb2(ctxt *Link) {
if thearch.Asmb2 != nil {
thearch.Asmb2(ctxt, ctxt.loader)
return
}
symSize = 0
spSize = 0
lcSize = 0
switch ctxt.HeadType {
default:
panic("unknown platform")
// Macho
case objabi.Hdarwin:
asmbMacho(ctxt)
// Plan9
case objabi.Hplan9:
asmbPlan9(ctxt)
// PE
case objabi.Hwindows:
asmbPe(ctxt)
// Xcoff
case objabi.Haix:
asmbXcoff(ctxt)
// Elf
case objabi.Hdragonfly,
objabi.Hfreebsd,
objabi.Hlinux,
objabi.Hnetbsd,
objabi.Hopenbsd,
objabi.Hsolaris:
asmbElf(ctxt)
}
if *FlagC {
fmt.Printf("textsize=%d\n", Segtext.Filelen)
fmt.Printf("datsize=%d\n", Segdata.Filelen)
fmt.Printf("bsssize=%d\n", Segdata.Length-Segdata.Filelen)
fmt.Printf("symsize=%d\n", symSize)
fmt.Printf("lcsize=%d\n", lcSize)
fmt.Printf("total=%d\n", Segtext.Filelen+Segdata.Length+uint64(symSize)+uint64(lcSize))
}
}
// writePlan9Header writes out the plan9 header at the present position in the OutBuf.
func writePlan9Header(buf *OutBuf, magic uint32, entry int64, is64Bit bool) {
if is64Bit {
magic |= 0x00008000
}
buf.Write32b(magic)
buf.Write32b(uint32(Segtext.Filelen))
buf.Write32b(uint32(Segdata.Filelen))
buf.Write32b(uint32(Segdata.Length - Segdata.Filelen))
buf.Write32b(uint32(symSize))
if is64Bit {
buf.Write32b(uint32(entry &^ 0x80000000))
} else {
buf.Write32b(uint32(entry))
}
buf.Write32b(uint32(spSize))
buf.Write32b(uint32(lcSize))
// amd64 includes the entry at the beginning of the symbol table.
if is64Bit {
buf.Write64b(uint64(entry))
}
}
// asmbPlan9 assembles a plan 9 binary.
func asmbPlan9(ctxt *Link) {
if !*FlagS {
*FlagS = true
symo := int64(Segdata.Fileoff + Segdata.Filelen)
ctxt.Out.SeekSet(symo)
asmbPlan9Sym(ctxt)
}
ctxt.Out.SeekSet(0)
writePlan9Header(ctxt.Out, thearch.Plan9Magic, Entryvalue(ctxt), thearch.Plan9_64Bit)
}
// sizeExtRelocs precomputes the size needed for the reloc records,
// sets the size and offset for relocation records in each section,
// and mmap the output buffer with the proper size.
func sizeExtRelocs(ctxt *Link, relsize uint32) {
if relsize == 0 {
panic("sizeExtRelocs: relocation size not set")
}
var sz int64
for _, seg := range Segments {
for _, sect := range seg.Sections {
sect.Reloff = uint64(ctxt.Out.Offset() + sz)
sect.Rellen = uint64(relsize * sect.Relcount)
sz += int64(sect.Rellen)
}
}
filesz := ctxt.Out.Offset() + sz
err := ctxt.Out.Mmap(uint64(filesz))
if err != nil {
Exitf("mapping output file failed: %v", err)
}
}
// relocSectFn wraps the function writing relocations of a section
// for parallel execution. Returns the wrapped function and a wait
// group for which the caller should wait.
func relocSectFn(ctxt *Link, relocSect func(*Link, *OutBuf, *sym.Section, []loader.Sym)) (func(*Link, *sym.Section, []loader.Sym), *sync.WaitGroup) {
var fn func(ctxt *Link, sect *sym.Section, syms []loader.Sym)
var wg sync.WaitGroup
var sem chan int
if ctxt.Out.isMmapped() {
// Write sections in parallel.
sem = make(chan int, 2*runtime.GOMAXPROCS(0))
fn = func(ctxt *Link, sect *sym.Section, syms []loader.Sym) {
wg.Add(1)
sem <- 1
out, err := ctxt.Out.View(sect.Reloff)
if err != nil {
panic(err)
}
go func() {
relocSect(ctxt, out, sect, syms)
wg.Done()
<-sem
}()
}
} else {
// We cannot Mmap. Write sequentially.
fn = func(ctxt *Link, sect *sym.Section, syms []loader.Sym) {
relocSect(ctxt, ctxt.Out, sect, syms)
}
}
return fn, &wg
}
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