// Copyright 2013 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.
// Writing of Go object files.
//
// Originally, Go object files were Plan 9 object files, but no longer.
// Now they are more like standard object files, in that each symbol is defined
// by an associated memory image (bytes) and a list of relocations to apply
// during linking. We do not (yet?) use a standard file format, however.
// For now, the format is chosen to be as simple as possible to read and write.
// It may change for reasons of efficiency, or we may even switch to a
// standard file format if there are compelling benefits to doing so.
// See golang.org/s/go13linker for more background.
//
// The file format is:
//
// - magic header: "\x00\x00go13ld"
// - byte 1 - version number
// - sequence of strings giving dependencies (imported packages)
// - empty string (marks end of sequence)
// - sequence of defined symbols
// - byte 0xff (marks end of sequence)
// - magic footer: "\xff\xffgo13ld"
//
// All integers are stored in a zigzag varint format.
// See golang.org/s/go12symtab for a definition.
//
// Data blocks and strings are both stored as an integer
// followed by that many bytes.
//
// A symbol reference is a string name followed by a version.
// An empty name corresponds to a nil LSym* pointer.
//
// Each symbol is laid out as the following fields (taken from LSym*):
//
// - byte 0xfe (sanity check for synchronization)
// - type [int]
// - name [string]
// - version [int]
// - flags [int]
// 1 dupok
// - size [int]
// - gotype [symbol reference]
// - p [data block]
// - nr [int]
// - r [nr relocations, sorted by off]
//
// If type == STEXT, there are a few more fields:
//
// - args [int]
// - locals [int]
// - nosplit [int]
// - flags [int]
// 1 leaf
// 2 C function
// - nlocal [int]
// - local [nlocal automatics]
// - pcln [pcln table]
//
// Each relocation has the encoding:
//
// - off [int]
// - siz [int]
// - type [int]
// - add [int]
// - xadd [int]
// - sym [symbol reference]
// - xsym [symbol reference]
//
// Each local has the encoding:
//
// - asym [symbol reference]
// - offset [int]
// - type [int]
// - gotype [symbol reference]
//
// The pcln table has the encoding:
//
// - pcsp [data block]
// - pcfile [data block]
// - pcline [data block]
// - npcdata [int]
// - pcdata [npcdata data blocks]
// - nfuncdata [int]
// - funcdata [nfuncdata symbol references]
// - funcdatasym [nfuncdata ints]
// - nfile [int]
// - file [nfile symbol references]
//
// The file layout and meaning of type integers are architecture-independent.
//
// TODO(rsc): The file format is good for a first pass but needs work.
// - There are SymID in the object file that should really just be strings.
// - The actual symbol memory images are interlaced with the symbol
// metadata. They should be separated, to reduce the I/O required to
// load just the metadata.
// - The symbol references should be shortened, either with a symbol
// table or by using a simple backward index to an earlier mentioned symbol.
package obj
import (
"fmt"
"log"
"path/filepath"
"strings"
)
var outfile string
// The Go and C compilers, and the assembler, call writeobj to write
// out a Go object file. The linker does not call this; the linker
// does not write out object files.
func Writeobjdirect(ctxt *Link, b *Biobuf) {
var flag int
var s *LSym
var p *Prog
var plink *Prog
var a *Auto
// Build list of symbols, and assign instructions to lists.
// Ignore ctxt->plist boundaries. There are no guarantees there,
// and the C compilers and assemblers just use one big list.
var text *LSym
var curtext *LSym
var data *LSym
var etext *LSym
var edata *LSym
for pl := ctxt.Plist; pl != nil; pl = pl.Link {
for p = pl.Firstpc; p != nil; p = plink {
if ctxt.Debugasm != 0 && ctxt.Debugvlog != 0 {
fmt.Printf("obj: %v\n", p)
}
plink = p.Link
p.Link = nil
if p.As == AEND {
continue
}
if p.As == ATYPE {
// Assume each TYPE instruction describes
// a different local variable or parameter,
// so no dedup.
// Using only the TYPE instructions means
// that we discard location information about local variables
// in C and assembly functions; that information is inferred
// from ordinary references, because there are no TYPE
// instructions there. Without the type information, gdb can't
// use the locations, so we don't bother to save them.
// If something else could use them, we could arrange to
// preserve them.
if curtext == nil {
continue
}
a = new(Auto)
a.Asym = p.From.Sym
a.Aoffset = int32(p.From.Offset)
a.Name = int16(p.From.Name)
a.Gotype = p.From.Gotype
a.Link = curtext.Autom
curtext.Autom = a
continue
}
if p.As == AGLOBL {
s = p.From.Sym
tmp6 := s.Seenglobl
s.Seenglobl++
if tmp6 != 0 {
fmt.Printf("duplicate %v\n", p)
}
if s.Onlist != 0 {
log.Fatalf("symbol %s listed multiple times", s.Name)
}
s.Onlist = 1
if data == nil {
data = s
} else {
edata.Next = s
}
s.Next = nil
s.Size = p.To.Offset
if s.Type == 0 || s.Type == SXREF {
s.Type = SBSS
}
flag = int(p.From3.Offset)
if flag&DUPOK != 0 {
s.Dupok = 1
}
if flag&RODATA != 0 {
s.Type = SRODATA
} else if flag&NOPTR != 0 {
s.Type = SNOPTRBSS
}
edata = s
continue
}
if p.As == ADATA {
savedata(ctxt, p.From.Sym, p, "<input>")
continue
}
if p.As == ATEXT {
s = p.From.Sym
if s == nil {
// func _() { }
curtext = nil
continue
}
if s.Text != nil {
log.Fatalf("duplicate TEXT for %s", s.Name)
}
if s.Onlist != 0 {
log.Fatalf("symbol %s listed multiple times", s.Name)
}
s.Onlist = 1
if text == nil {
text = s
} else {
etext.Next = s
}
etext = s
flag = int(p.From3Offset())
if flag&DUPOK != 0 {
s.Dupok = 1
}
if flag&NOSPLIT != 0 {
s.Nosplit = 1
}
s.Next = nil
s.Type = STEXT
s.Text = p
s.Etext = p
curtext = s
continue
}
if p.As == AFUNCDATA {
// Rewrite reference to go_args_stackmap(SB) to the Go-provided declaration information.
if curtext == nil { // func _() {}
continue
}
if p.To.Sym.Name == "go_args_stackmap" {
if p.From.Type != TYPE_CONST || p.From.Offset != FUNCDATA_ArgsPointerMaps {
ctxt.Diag("FUNCDATA use of go_args_stackmap(SB) without FUNCDATA_ArgsPointerMaps")
}
p.To.Sym = Linklookup(ctxt, fmt.Sprintf("%s.args_stackmap", curtext.Name), int(curtext.Version))
}
}
if curtext == nil {
continue
}
s = curtext
s.Etext.Link = p
s.Etext = p
}
}
// Add reference to Go arguments for C or assembly functions without them.
var found int
for s := text; s != nil; s = s.Next {
if !strings.HasPrefix(s.Name, "\"\".") {
continue
}
found = 0
for p = s.Text; p != nil; p = p.Link {
if p.As == AFUNCDATA && p.From.Type == TYPE_CONST && p.From.Offset == FUNCDATA_ArgsPointerMaps {
found = 1
break
}
}
if found == 0 {
p = Appendp(ctxt, s.Text)
p.As = AFUNCDATA
p.From.Type = TYPE_CONST
p.From.Offset = FUNCDATA_ArgsPointerMaps
p.To.Type = TYPE_MEM
p.To.Name = NAME_EXTERN
p.To.Sym = Linklookup(ctxt, fmt.Sprintf("%s.args_stackmap", s.Name), int(s.Version))
}
}
// Turn functions into machine code images.
for s := text; s != nil; s = s.Next {
mkfwd(s)
linkpatch(ctxt, s)
ctxt.Arch.Follow(ctxt, s)
ctxt.Arch.Preprocess(ctxt, s)
ctxt.Arch.Assemble(ctxt, s)
linkpcln(ctxt, s)
}
// Emit header.
Bputc(b, 0)
Bputc(b, 0)
fmt.Fprintf(b, "go13ld")
Bputc(b, 1) // version
// Emit autolib.
for _, pkg := range ctxt.Imports {
wrstring(b, pkg)
}
wrstring(b, "")
// Emit symbols.
for s := text; s != nil; s = s.Next {
writesym(ctxt, b, s)
}
for s := data; s != nil; s = s.Next {
writesym(ctxt, b, s)
}
// Emit footer.
Bputc(b, 0xff)
Bputc(b, 0xff)
fmt.Fprintf(b, "go13ld")
}
func writesym(ctxt *Link, b *Biobuf, s *LSym) {
if ctxt.Debugasm != 0 {
fmt.Fprintf(ctxt.Bso, "%s ", s.Name)
if s.Version != 0 {
fmt.Fprintf(ctxt.Bso, "v=%d ", s.Version)
}
if s.Type != 0 {
fmt.Fprintf(ctxt.Bso, "t=%d ", s.Type)
}
if s.Dupok != 0 {
fmt.Fprintf(ctxt.Bso, "dupok ")
}
if s.Cfunc != 0 {
fmt.Fprintf(ctxt.Bso, "cfunc ")
}
if s.Nosplit != 0 {
fmt.Fprintf(ctxt.Bso, "nosplit ")
}
fmt.Fprintf(ctxt.Bso, "size=%d value=%d", int64(s.Size), int64(s.Value))
if s.Type == STEXT {
fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x", uint64(s.Args), uint64(s.Locals))
if s.Leaf != 0 {
fmt.Fprintf(ctxt.Bso, " leaf")
}
}
fmt.Fprintf(ctxt.Bso, "\n")
for p := s.Text; p != nil; p = p.Link {
fmt.Fprintf(ctxt.Bso, "\t%#04x %v\n", uint(int(p.Pc)), p)
}
var c int
var j int
for i := 0; i < len(s.P); {
fmt.Fprintf(ctxt.Bso, "\t%#04x", uint(i))
for j = i; j < i+16 && j < len(s.P); j++ {
fmt.Fprintf(ctxt.Bso, " %02x", s.P[j])
}
for ; j < i+16; j++ {
fmt.Fprintf(ctxt.Bso, " ")
}
fmt.Fprintf(ctxt.Bso, " ")
for j = i; j < i+16 && j < len(s.P); j++ {
c = int(s.P[j])
if ' ' <= c && c <= 0x7e {
fmt.Fprintf(ctxt.Bso, "%c", c)
} else {
fmt.Fprintf(ctxt.Bso, ".")
}
}
fmt.Fprintf(ctxt.Bso, "\n")
i += 16
}
var r *Reloc
var name string
for i := 0; i < len(s.R); i++ {
r = &s.R[i]
name = ""
if r.Sym != nil {
name = r.Sym.Name
}
if ctxt.Arch.Thechar == '5' || ctxt.Arch.Thechar == '9' {
fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s+%x\n", int(r.Off), r.Siz, r.Type, name, uint64(int64(r.Add)))
} else {
fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s+%d\n", int(r.Off), r.Siz, r.Type, name, int64(r.Add))
}
}
}
Bputc(b, 0xfe)
wrint(b, int64(s.Type))
wrstring(b, s.Name)
wrint(b, int64(s.Version))
flags := int64(s.Dupok)
if s.Local {
flags |= 2
}
wrint(b, flags)
wrint(b, s.Size)
wrsym(b, s.Gotype)
wrdata(b, s.P)
wrint(b, int64(len(s.R)))
var r *Reloc
for i := 0; i < len(s.R); i++ {
r = &s.R[i]
wrint(b, int64(r.Off))
wrint(b, int64(r.Siz))
wrint(b, int64(r.Type))
wrint(b, r.Add)
wrint(b, 0) // Xadd, ignored
wrsym(b, r.Sym)
wrsym(b, nil) // Xsym, ignored
}
if s.Type == STEXT {
wrint(b, int64(s.Args))
wrint(b, int64(s.Locals))
wrint(b, int64(s.Nosplit))
wrint(b, int64(s.Leaf)|int64(s.Cfunc)<<1)
n := 0
for a := s.Autom; a != nil; a = a.Link {
n++
}
wrint(b, int64(n))
for a := s.Autom; a != nil; a = a.Link {
wrsym(b, a.Asym)
wrint(b, int64(a.Aoffset))
if a.Name == NAME_AUTO {
wrint(b, A_AUTO)
} else if a.Name == NAME_PARAM {
wrint(b, A_PARAM)
} else {
log.Fatalf("%s: invalid local variable type %d", s.Name, a.Name)
}
wrsym(b, a.Gotype)
}
pc := s.Pcln
wrdata(b, pc.Pcsp.P)
wrdata(b, pc.Pcfile.P)
wrdata(b, pc.Pcline.P)
wrint(b, int64(len(pc.Pcdata)))
for i := 0; i < len(pc.Pcdata); i++ {
wrdata(b, pc.Pcdata[i].P)
}
wrint(b, int64(len(pc.Funcdataoff)))
for i := 0; i < len(pc.Funcdataoff); i++ {
wrsym(b, pc.Funcdata[i])
}
for i := 0; i < len(pc.Funcdataoff); i++ {
wrint(b, pc.Funcdataoff[i])
}
wrint(b, int64(len(pc.File)))
for i := 0; i < len(pc.File); i++ {
wrpathsym(ctxt, b, pc.File[i])
}
}
}
// Reusable buffer to avoid allocations.
// This buffer was responsible for 15% of gc's allocations.
var varintbuf [10]uint8
func wrint(b *Biobuf, sval int64) {
var v uint64
uv := (uint64(sval) << 1) ^ uint64(int64(sval>>63))
p := varintbuf[:]
for v = uv; v >= 0x80; v >>= 7 {
p[0] = uint8(v | 0x80)
p = p[1:]
}
p[0] = uint8(v)
p = p[1:]
b.Write(varintbuf[:len(varintbuf)-len(p)])
}
func wrstring(b *Biobuf, s string) {
wrint(b, int64(len(s)))
b.w.WriteString(s)
}
// wrpath writes a path just like a string, but on windows, it
// translates '\\' to '/' in the process.
func wrpath(ctxt *Link, b *Biobuf, p string) {
wrstring(b, filepath.ToSlash(p))
}
func wrdata(b *Biobuf, v []byte) {
wrint(b, int64(len(v)))
b.Write(v)
}
func wrpathsym(ctxt *Link, b *Biobuf, s *LSym) {
if s == nil {
wrint(b, 0)
wrint(b, 0)
return
}
wrpath(ctxt, b, s.Name)
wrint(b, int64(s.Version))
}
func wrsym(b *Biobuf, s *LSym) {
if s == nil {
wrint(b, 0)
wrint(b, 0)
return
}
wrstring(b, s.Name)
wrint(b, int64(s.Version))
}