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cmd/link, cmd/compile: Add symbol references to object file.
Symbols in the object file currently refer to each other using symbol name and version. Referring to the same symbol many times in an object file takes up space and causes redundant map lookups. Instead write out a list of unique symbol references and have symbols refer to each other using indexes into this list. Credit to Michael Hudson-Doyle for kicking this off. Reduces pkg/linux_amd64 size by 30% from 61MB to 43MB name old s/op new s/op delta LinkCmdGo 0.74 ± 3% 0.63 ± 4% -15.22% (p=0.000 n=20+20) LinkJuju 6.38 ± 6% 5.73 ± 6% -10.16% (p=0.000 n=20+19) Change-Id: I7e101a0c80b8e673a3ba688295e6f80ea04e1cfb Reviewed-on: https://go-review.googlesource.com/20099 Reviewed-by: David Crawshaw <crawshaw@golang.org> Run-TryBot: David Crawshaw <crawshaw@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Shahar Kohanim
David Crawshaw
parent
ea4b785ae0
commit
3648d2d4cd
6 changed files with 146 additions and 73 deletions
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@ -19,6 +19,8 @@
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// - byte 1 - version number
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// - sequence of strings giving dependencies (imported packages)
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// - empty string (marks end of sequence)
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// - sequence of sybol references used by the defined symbols
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// - byte 0xff (marks end of sequence)
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// - sequence of defined symbols
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// - byte 0xff (marks end of sequence)
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// - magic footer: "\xff\xffgo13ld"
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@ -30,18 +32,21 @@
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// followed by that many bytes.
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//
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// A symbol reference is a string name followed by a version.
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// An empty name corresponds to a nil LSym* pointer.
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//
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// A symbol points to other symbols using an index into the symbol
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// reference sequence. Index 0 corresponds to a nil LSym* pointer.
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// In the symbol layout described below "symref index" stands for this
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// index.
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//
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// Each symbol is laid out as the following fields (taken from LSym*):
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//
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// - byte 0xfe (sanity check for synchronization)
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// - type [int]
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// - name [string]
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// - version [int]
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// - name & version [symref index]
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// - flags [int]
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// 1 dupok
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// - size [int]
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// - gotype [symbol reference]
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// - gotype [symref index]
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// - p [data block]
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// - nr [int]
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// - r [nr relocations, sorted by off]
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@ -52,8 +57,9 @@
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// - locals [int]
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// - nosplit [int]
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// - flags [int]
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// 1 leaf
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// 2 C function
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// 1<<0 leaf
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// 1<<1 C function
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// 1<<2 function may call reflect.Type.Method
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// - nlocal [int]
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// - local [nlocal automatics]
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// - pcln [pcln table]
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@ -65,15 +71,15 @@
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// - type [int]
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// - add [int]
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// - xadd [int]
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// - sym [symbol reference]
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// - xsym [symbol reference]
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// - sym [symref index]
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// - xsym [symref index]
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//
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// Each local has the encoding:
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//
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// - asym [symbol reference]
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// - asym [symref index]
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// - offset [int]
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// - type [int]
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// - gotype [symbol reference]
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// - gotype [symref index]
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//
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// The pcln table has the encoding:
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//
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@ -83,10 +89,10 @@
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// - npcdata [int]
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// - pcdata [npcdata data blocks]
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// - nfuncdata [int]
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// - funcdata [nfuncdata symbol references]
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// - funcdata [nfuncdata symref index]
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// - funcdatasym [nfuncdata ints]
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// - nfile [int]
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// - file [nfile symbol references]
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// - file [nfile symref index]
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//
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// The file layout and meaning of type integers are architecture-independent.
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//
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@ -95,8 +101,6 @@
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// - The actual symbol memory images are interlaced with the symbol
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// metadata. They should be separated, to reduce the I/O required to
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// load just the metadata.
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// - The symbol references should be shortened, either with a symbol
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// table or by using a simple backward index to an earlier mentioned symbol.
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package obj
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@ -335,6 +339,15 @@ func Writeobjfile(ctxt *Link, b *Biobuf) {
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}
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wrstring(b, "")
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// Emit symbol references.
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for s := ctxt.Text; s != nil; s = s.Next {
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writerefs(ctxt, b, s)
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}
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for s := ctxt.Data; s != nil; s = s.Next {
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writerefs(ctxt, b, s)
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}
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Bputc(b, 0xff)
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// Emit symbols.
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for s := ctxt.Text; s != nil; s = s.Next {
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writesym(ctxt, b, s)
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@ -350,6 +363,43 @@ func Writeobjfile(ctxt *Link, b *Biobuf) {
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fmt.Fprintf(b, "go13ld")
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}
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func wrref(ctxt *Link, b *Biobuf, s *LSym, isPath bool) {
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if s == nil || s.RefIdx != 0 {
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return
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}
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Bputc(b, 0xfe)
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if isPath {
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wrstring(b, filepath.ToSlash(s.Name))
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} else {
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wrstring(b, s.Name)
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}
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wrint(b, int64(s.Version))
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ctxt.RefsWritten++
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s.RefIdx = ctxt.RefsWritten
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}
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func writerefs(ctxt *Link, b *Biobuf, s *LSym) {
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wrref(ctxt, b, s, false)
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wrref(ctxt, b, s.Gotype, false)
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for i := range s.R {
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wrref(ctxt, b, s.R[i].Sym, false)
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}
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if s.Type == STEXT {
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for a := s.Autom; a != nil; a = a.Link {
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wrref(ctxt, b, a.Asym, false)
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wrref(ctxt, b, a.Gotype, false)
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}
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pc := s.Pcln
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for _, d := range pc.Funcdata {
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wrref(ctxt, b, d, false)
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}
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for _, f := range pc.File {
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wrref(ctxt, b, f, true)
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}
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}
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}
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func writesym(ctxt *Link, b *Biobuf, s *LSym) {
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if ctxt.Debugasm != 0 {
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fmt.Fprintf(ctxt.Bso, "%s ", s.Name)
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@ -420,8 +470,7 @@ func writesym(ctxt *Link, b *Biobuf, s *LSym) {
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Bputc(b, 0xfe)
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wrint(b, int64(s.Type))
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wrstring(b, s.Name)
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wrint(b, int64(s.Version))
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wrsym(b, s)
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flags := int64(s.Dupok)
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if s.Local {
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flags |= 2
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@ -487,8 +536,8 @@ func writesym(ctxt *Link, b *Biobuf, s *LSym) {
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wrint(b, pc.Funcdataoff[i])
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}
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wrint(b, int64(len(pc.File)))
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for i := 0; i < len(pc.File); i++ {
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wrpathsym(ctxt, b, pc.File[i])
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for _, f := range pc.File {
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wrsym(b, f)
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}
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}
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}
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@ -515,37 +564,20 @@ func wrstring(b *Biobuf, s string) {
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b.w.WriteString(s)
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}
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// wrpath writes a path just like a string, but on windows, it
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// translates '\\' to '/' in the process.
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func wrpath(ctxt *Link, b *Biobuf, p string) {
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wrstring(b, filepath.ToSlash(p))
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}
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func wrdata(b *Biobuf, v []byte) {
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wrint(b, int64(len(v)))
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b.Write(v)
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}
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func wrpathsym(ctxt *Link, b *Biobuf, s *LSym) {
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if s == nil {
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wrint(b, 0)
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wrint(b, 0)
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return
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}
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wrpath(ctxt, b, s.Name)
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wrint(b, int64(s.Version))
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}
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func wrsym(b *Biobuf, s *LSym) {
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if s == nil {
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wrint(b, 0)
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wrint(b, 0)
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return
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}
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wrstring(b, s.Name)
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wrint(b, int64(s.Version))
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if s.RefIdx == 0 {
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log.Fatalln("writing an unreferenced symbol", s.Name)
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}
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wrint(b, int64(s.RefIdx))
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}
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// relocByOff sorts relocations by their offsets.
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