cmd/link: generate DWARF info using symbols

This updates dwarf.go to generate debug information as symbols
instead of directly writing to the output file. This should make
it easier to move generation of some of the debug info into the compiler.

Change-Id: Id2358988bfb689865ab4d68f82716f0676336df4
Reviewed-on: https://go-review.googlesource.com/20679
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/link.go

@@ -423,6 +423,8 @@ const (
 	SCONST
 	SDYNIMPORT
 	SHOSTOBJ
+	SDWARFSECT
+	SDWARFINFO
 	SSUB       = 1 << 8
 	SMASK      = SSUB - 1
 	SHIDDEN    = 1 << 9
@@ -495,6 +497,8 @@ const (
 	// of a JMP instruction, by encoding the address into the instruction.
 	// The stack nosplit check ignores this since it is not a function call.
 	R_JMPMIPS
+	// R_DWARFREF resolves to the offset of the symbol from its section.
+	R_DWARFREF
 
 	// Platform dependent relocations. Architectures with fixed width instructions
 	// have the inherent issue that a 32-bit (or 64-bit!) displacement cannot be

src/cmd/link/internal/amd64/asm.go

@@ -650,19 +650,11 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	machlink := int64(0)
 	if ld.HEADTYPE == obj.Hdarwin {
-		if ld.Debug['v'] != 0 {
-			fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-		}
-
-		dwarfoff := ld.Rnd(int64(uint64(ld.HEADR)+ld.Segtext.Length), int64(ld.INITRND)) + ld.Rnd(int64(ld.Segdata.Filelen), int64(ld.INITRND))
-		ld.Cseek(dwarfoff)
-
-		ld.Segdwarf.Fileoff = uint64(ld.Cpos())
-		ld.Dwarfemitdebugsections()
-		ld.Segdwarf.Filelen = uint64(ld.Cpos()) - ld.Segdwarf.Fileoff
-
 		machlink = ld.Domacholink()
 	}
 
@@ -715,11 +707,11 @@ func asmb() {
 			obj.Hdragonfly,
 			obj.Hsolaris,
 			obj.Hnacl:
-			symo = int64(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+			symo = int64(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 			symo = ld.Rnd(symo, int64(ld.INITRND))
 
 		case obj.Hwindows:
-			symo = int64(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+			symo = int64(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 			symo = ld.Rnd(symo, ld.PEFILEALIGN)
 		}
 
@@ -736,8 +728,6 @@ func asmb() {
 					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
 				}
 
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}
@@ -762,8 +752,6 @@ func asmb() {
 				fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
 			}
 
-			ld.Dwarfemitdebugsections()
-
 		case obj.Hdarwin:
 			if ld.Linkmode == ld.LinkExternal {
 				ld.Machoemitreloc()

src/cmd/link/internal/arm/asm.go

@@ -597,19 +597,11 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	machlink := uint32(0)
 	if ld.HEADTYPE == obj.Hdarwin {
-		if ld.Debug['v'] != 0 {
-			fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-		}
-
-		dwarfoff := uint32(ld.Rnd(int64(uint64(ld.HEADR)+ld.Segtext.Length), int64(ld.INITRND)) + ld.Rnd(int64(ld.Segdata.Filelen), int64(ld.INITRND)))
-		ld.Cseek(int64(dwarfoff))
-
-		ld.Segdwarf.Fileoff = uint64(ld.Cpos())
-		ld.Dwarfemitdebugsections()
-		ld.Segdwarf.Filelen = uint64(ld.Cpos()) - ld.Segdwarf.Fileoff
-
 		machlink = uint32(ld.Domacholink())
 	}
 
@@ -627,7 +619,7 @@ func asmb() {
 		switch ld.HEADTYPE {
 		default:
 			if ld.Iself {
-				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 				symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 			}
 
@@ -649,11 +641,6 @@ func asmb() {
 				ld.Cflush()
 				ld.Cwrite(ld.Elfstrdat)
 
-				if ld.Debug['v'] != 0 {
-					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-				}
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}

src/cmd/link/internal/arm64/asm.go

@@ -435,19 +435,11 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	machlink := uint32(0)
 	if ld.HEADTYPE == obj.Hdarwin {
-		if ld.Debug['v'] != 0 {
-			fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-		}
-
-		dwarfoff := uint32(ld.Rnd(int64(uint64(ld.HEADR)+ld.Segtext.Length), int64(ld.INITRND)) + ld.Rnd(int64(ld.Segdata.Filelen), int64(ld.INITRND)))
-		ld.Cseek(int64(dwarfoff))
-
-		ld.Segdwarf.Fileoff = uint64(ld.Cpos())
-		ld.Dwarfemitdebugsections()
-		ld.Segdwarf.Filelen = uint64(ld.Cpos()) - ld.Segdwarf.Fileoff
-
 		machlink = uint32(ld.Domacholink())
 	}
 
@@ -465,7 +457,7 @@ func asmb() {
 		switch ld.HEADTYPE {
 		default:
 			if ld.Iself {
-				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 				symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 			}
 
@@ -487,11 +479,6 @@ func asmb() {
 				ld.Cflush()
 				ld.Cwrite(ld.Elfstrdat)
 
-				if ld.Debug['v'] != 0 {
-					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-				}
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}

src/cmd/link/internal/ld/data.go

@@ -84,6 +84,20 @@ func setuintxx(ctxt *Link, s *LSym, off int64, v uint64, wid int64) int64 {
 	return off + wid
 }
 
+func Addbytes(ctxt *Link, s *LSym, bytes []byte) int64 {
+	if s.Type == 0 {
+		s.Type = obj.SDATA
+	}
+	s.Attr |= AttrReachable
+	s.Size += int64(len(bytes))
+	if int64(int(s.Size)) != s.Size {
+		log.Fatalf("Addbytes size %d too long", s.Size)
+	}
+	s.P = append(s.P, bytes...)
+
+	return s.Size
+}
+
 func adduintxx(ctxt *Link, s *LSym, v uint64, wid int) int64 {
 	off := s.Size
 	setuintxx(ctxt, s, off, v, int64(wid))
@@ -489,6 +503,25 @@ func relocsym(s *LSym) {
 				errorexit()
 			}
 
+		case obj.R_DWARFREF:
+			if r.Sym.Sect == nil {
+				Diag("missing DWARF section: %s from %s", r.Sym.Name, s.Name)
+			}
+			if Linkmode == LinkExternal {
+				r.Done = 0
+				r.Type = obj.R_ADDR
+
+				r.Xsym = Linkrlookup(Ctxt, r.Sym.Sect.Name, 0)
+				r.Xadd = r.Add + Symaddr(r.Sym) - int64(r.Sym.Sect.Vaddr)
+				o = r.Xadd
+				rs = r.Xsym
+				if Iself && Thearch.Thechar == '6' {
+					o = 0
+				}
+				break
+			}
+			o = Symaddr(r.Sym) + r.Add - int64(r.Sym.Sect.Vaddr)
+
 			// r->sym can be null when CALL $(constant) is transformed from absolute PC to relative PC call.
 		case obj.R_CALL, obj.R_GOTPCREL, obj.R_PCREL:
 			if Linkmode == LinkExternal && r.Sym != nil && r.Sym.Type != obj.SCONST && (r.Sym.Sect != Ctxt.Cursym.Sect || r.Type == obj.R_GOTPCREL) {
@@ -614,6 +647,9 @@ func reloc() {
 	for s := datap; s != nil; s = s.Next {
 		relocsym(s)
 	}
+	for s := dwarfp; s != nil; s = s.Next {
+		relocsym(s)
+	}
 }
 
 func dynrelocsym(s *LSym) {
@@ -893,6 +929,14 @@ func Datblk(addr int64, size int64) {
 	fmt.Fprintf(&Bso, "\t%.8x|\n", uint(eaddr))
 }
 
+func Dwarfblk(addr int64, size int64) {
+	if Debug['a'] != 0 {
+		fmt.Fprintf(&Bso, "dwarfblk [%#x,%#x) at offset %#x\n", addr, addr+size, Cpos())
+	}
+
+	blk(dwarfp, addr, size)
+}
+
 var zeros [512]byte
 
 // strnput writes the first n bytes of s.
@@ -1691,6 +1735,40 @@ func dodata() {
 		Diag("read-only data segment too large")
 	}
 
+	dwarfgeneratedebugsyms()
+
+	for s = dwarfp; s != nil && s.Type == obj.SDWARFSECT; s = s.Next {
+		sect = addsection(&Segdwarf, s.Name, 04)
+		sect.Align = 1
+		datsize = Rnd(datsize, int64(sect.Align))
+		sect.Vaddr = uint64(datsize)
+		s.Sect = sect
+		s.Type = obj.SRODATA
+		s.Value = int64(uint64(datsize) - sect.Vaddr)
+		growdatsize(&datsize, s)
+		sect.Length = uint64(datsize) - sect.Vaddr
+	}
+
+	if s != nil {
+		sect = addsection(&Segdwarf, ".debug_info", 04)
+		sect.Align = 1
+		datsize = Rnd(datsize, int64(sect.Align))
+		sect.Vaddr = uint64(datsize)
+		for ; s != nil && s.Type == obj.SDWARFINFO; s = s.Next {
+			s.Sect = sect
+			s.Type = obj.SRODATA
+			s.Value = int64(uint64(datsize) - sect.Vaddr)
+			s.Attr |= AttrLocal
+			growdatsize(&datsize, s)
+		}
+		sect.Length = uint64(datsize) - sect.Vaddr
+	}
+
+	// The compiler uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
+	if datsize != int64(uint32(datsize)) {
+		Diag("dwarf segment too large")
+	}
+
 	/* number the sections */
 	n := int32(1)
 
@@ -1706,6 +1784,10 @@ func dodata() {
 		sect.Extnum = int16(n)
 		n++
 	}
+	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+		sect.Extnum = int16(n)
+		n++
+	}
 }
 
 // Add buildid to beginning of text segment, on non-ELF systems.
@@ -1857,6 +1939,29 @@ func address() {
 
 	Segdata.Filelen = bss.Vaddr - Segdata.Vaddr
 
+	va = uint64(Rnd(int64(va), int64(INITRND)))
+	Segdwarf.Rwx = 06
+	Segdwarf.Vaddr = va
+	Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), int64(INITRND)))
+	Segdwarf.Filelen = 0
+	if HEADTYPE == obj.Hwindows {
+		Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), int64(PEFILEALIGN)))
+	}
+	for s := Segdwarf.Sect; s != nil; s = s.Next {
+		vlen = int64(s.Length)
+		if s.Next != nil {
+			vlen = int64(s.Next.Vaddr - s.Vaddr)
+		}
+		s.Vaddr = va
+		va += uint64(vlen)
+		if HEADTYPE == obj.Hwindows {
+			va = uint64(Rnd(int64(va), PEFILEALIGN))
+		}
+		Segdwarf.Length = va - Segdwarf.Vaddr
+	}
+
+	Segdwarf.Filelen = va - Segdwarf.Vaddr
+
 	text := Segtext.Sect
 	var rodata *Section
 	if Segrodata.Sect != nil {
@@ -1884,6 +1989,15 @@ func address() {
 			sub.Value += sym.Value
 		}
 	}
+	for sym := dwarfp; sym != nil; sym = sym.Next {
+		Ctxt.Cursym = sym
+		if sym.Sect != nil {
+			sym.Value += int64(sym.Sect.Vaddr)
+		}
+		for sub = sym.Sub; sub != nil; sub = sub.Sub {
+			sub.Value += sym.Value
+		}
+	}
 
 	if Buildmode == BuildmodeShared {
 		s := Linklookup(Ctxt, "go.link.abihashbytes", 0)

src/cmd/link/internal/ld/elf.go

@@ -1622,6 +1622,9 @@ func elfshbits(sect *Section) *ElfShdr {
 		sh.flags |= SHF_TLS
 		sh.type_ = SHT_NOBITS
 	}
+	if strings.HasPrefix(sect.Name, ".debug") {
+		sh.flags = 0
+	}
 
 	if Linkmode != LinkExternal {
 		sh.addr = sect.Vaddr
@@ -1739,6 +1742,9 @@ func Elfemitreloc() {
 	for sect := Segdata.Sect; sect != nil; sect = sect.Next {
 		elfrelocsect(sect, datap)
 	}
+	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+		elfrelocsect(sect, dwarfp)
+	}
 }
 
 func addgonote(sectionName string, tag uint32, desc []byte) {
@@ -2067,6 +2073,9 @@ func Asmbelfsetup() {
 	for sect := Segdata.Sect; sect != nil; sect = sect.Next {
 		elfshalloc(sect)
 	}
+	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+		elfshalloc(sect)
+	}
 }
 
 func Asmbelf(symo int64) {
@@ -2432,6 +2441,9 @@ elfobj:
 	for sect := Segdata.Sect; sect != nil; sect = sect.Next {
 		elfshbits(sect)
 	}
+	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+		elfshbits(sect)
+	}
 
 	if Linkmode == LinkExternal {
 		for sect := Segtext.Sect; sect != nil; sect = sect.Next {
@@ -2443,7 +2455,14 @@ elfobj:
 		for sect := Segdata.Sect; sect != nil; sect = sect.Next {
 			elfshreloc(sect)
 		}
-
+		for s := dwarfp; s != nil; s = s.Next {
+			if len(s.R) > 0 || s.Type == obj.SDWARFINFO {
+				elfshreloc(s.Sect)
+			}
+			if s.Type == obj.SDWARFINFO {
+				break
+			}
+		}
 		// add a .note.GNU-stack section to mark the stack as non-executable
 		sh := elfshname(".note.GNU-stack")
 
@@ -2467,8 +2486,6 @@ elfobj:
 		sh.off = uint64(symo) + uint64(Symsize)
 		sh.size = uint64(len(Elfstrdat))
 		sh.addralign = 1
-
-		dwarfaddelfheaders()
 	}
 
 	/* Main header */

src/cmd/link/internal/ld/macho.go

@@ -356,7 +356,7 @@ func machoshbits(mseg *MachoSeg, sect *Section, segname string) {
 	buf := "__" + strings.Replace(sect.Name[1:], ".", "_", -1)
 
 	var msect *MachoSect
-	if sect.Rwx&1 == 0 && (Thearch.Thechar == '7' || // arm64
+	if sect.Rwx&1 == 0 && segname != "__DWARF" && (Thearch.Thechar == '7' || // arm64
 		(Thearch.Thechar == '6' && (Buildmode == BuildmodeCShared || Buildmode == BuildmodeCArchive))) { // amd64
 		// Darwin external linker on arm64 and on amd64 in c-shared/c-archive buildmode
 		// complains about absolute relocs in __TEXT, so if the section is not
@@ -411,6 +411,10 @@ func machoshbits(mseg *MachoSeg, sect *Section, segname string) {
 		msect.name = "__mod_init_func"
 		msect.flag = 9 // S_MOD_INIT_FUNC_POINTERS
 	}
+
+	if segname == "__DWARF" {
+		msect.flag |= 0x02000000
+	}
 }
 
 func Asmbmacho() {
@@ -492,6 +496,20 @@ func Asmbmacho() {
 		machoshbits(ms, sect, "__DATA")
 	}
 
+	/* dwarf */
+	if Debug['w'] == 0 {
+		if Linkmode != LinkExternal {
+			ms = newMachoSeg("__DWARF", 20)
+			ms.vaddr = Segdwarf.Vaddr
+			ms.vsize = 0
+			ms.fileoffset = Segdwarf.Fileoff
+			ms.filesize = Segdwarf.Filelen
+		}
+		for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+			machoshbits(ms, sect, "__DWARF")
+		}
+	}
+
 	if Linkmode != LinkExternal {
 		switch Thearch.Thechar {
 		default:
@@ -586,11 +604,6 @@ func Asmbmacho() {
 		ml.data[1] = 10<<16 | 7<<8 | 0<<0 // SDK 10.7.0
 	}
 
-	// TODO: dwarf headers go in ms too
-	if Debug['s'] == 0 {
-		dwarfaddmachoheaders(ms)
-	}
-
 	a := machowrite()
 	if int32(a) > HEADR {
 		Exitf("HEADR too small: %d > %d", a, HEADR)
@@ -876,5 +889,7 @@ func Machoemitreloc() {
 	for sect := Segdata.Sect; sect != nil; sect = sect.Next {
 		machorelocsect(sect, datap)
 	}
-	dwarfemitreloc()
+	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
+		machorelocsect(sect, dwarfp)
+	}
 }

src/cmd/link/internal/ld/symtab.go

@@ -195,18 +195,6 @@ func putelfsectionsym(s *LSym, shndx int) {
 	numelfsym++
 }
 
-func putelfsymshndx(sympos int64, shndx int) {
-	here := Cpos()
-	if elf64 {
-		Cseek(sympos + 6)
-	} else {
-		Cseek(sympos + 14)
-	}
-
-	Thearch.Wput(uint16(shndx))
-	Cseek(here)
-}
-
 func Asmelfsym() {
 	// the first symbol entry is reserved
 	putelfsyment(0, 0, 0, STB_LOCAL<<4|STT_NOTYPE, 0, 0)

src/cmd/link/internal/mips64/asm.go

@@ -147,6 +147,9 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	/* output symbol table */
 	ld.Symsize = 0
 
@@ -161,7 +164,7 @@ func asmb() {
 		switch ld.HEADTYPE {
 		default:
 			if ld.Iself {
-				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 				symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 			}
 
@@ -180,11 +183,6 @@ func asmb() {
 				ld.Cflush()
 				ld.Cwrite(ld.Elfstrdat)
 
-				if ld.Debug['v'] != 0 {
-					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-				}
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}

src/cmd/link/internal/ppc64/asm.go

@@ -868,6 +868,9 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	/* output symbol table */
 	ld.Symsize = 0
 
@@ -882,7 +885,7 @@ func asmb() {
 		switch ld.HEADTYPE {
 		default:
 			if ld.Iself {
-				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 				symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 			}
 
@@ -901,11 +904,6 @@ func asmb() {
 				ld.Cflush()
 				ld.Cwrite(ld.Elfstrdat)
 
-				if ld.Debug['v'] != 0 {
-					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-				}
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}

src/cmd/link/internal/s390x/asm.go

@@ -539,6 +539,9 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	/* output symbol table */
 	ld.Symsize = 0
 
@@ -552,7 +555,7 @@ func asmb() {
 			fmt.Fprintf(&ld.Bso, "%5.2f sym\n", obj.Cputime())
 		}
 		ld.Bso.Flush()
-		symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+		symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 		symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 
 		ld.Cseek(int64(symo))
@@ -566,7 +569,6 @@ func asmb() {
 		if ld.Debug['v'] != 0 {
 			fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
 		}
-		ld.Dwarfemitdebugsections()
 
 		if ld.Linkmode == ld.LinkExternal {
 			ld.Elfemitreloc()

src/cmd/link/internal/x86/asm.go

@@ -643,19 +643,11 @@ func asmb() {
 	ld.Cseek(int64(ld.Segdata.Fileoff))
 	ld.Datblk(int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
 
+	ld.Cseek(int64(ld.Segdwarf.Fileoff))
+	ld.Dwarfblk(int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+
 	machlink := uint32(0)
 	if ld.HEADTYPE == obj.Hdarwin {
-		if ld.Debug['v'] != 0 {
-			fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-		}
-
-		dwarfoff := uint32(ld.Rnd(int64(uint64(ld.HEADR)+ld.Segtext.Length), int64(ld.INITRND)) + ld.Rnd(int64(ld.Segdata.Filelen), int64(ld.INITRND)))
-		ld.Cseek(int64(dwarfoff))
-
-		ld.Segdwarf.Fileoff = uint64(ld.Cpos())
-		ld.Dwarfemitdebugsections()
-		ld.Segdwarf.Filelen = uint64(ld.Cpos()) - ld.Segdwarf.Fileoff
-
 		machlink = uint32(ld.Domacholink())
 	}
 
@@ -672,7 +664,7 @@ func asmb() {
 		switch ld.HEADTYPE {
 		default:
 			if ld.Iself {
-				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 				symo = uint32(ld.Rnd(int64(symo), int64(ld.INITRND)))
 			}
 
@@ -683,7 +675,7 @@ func asmb() {
 			symo = uint32(ld.Segdwarf.Fileoff + uint64(ld.Rnd(int64(ld.Segdwarf.Filelen), int64(ld.INITRND))) + uint64(machlink))
 
 		case obj.Hwindows:
-			symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
+			symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
 			symo = uint32(ld.Rnd(int64(symo), ld.PEFILEALIGN))
 		}
 
@@ -698,11 +690,6 @@ func asmb() {
 				ld.Cflush()
 				ld.Cwrite(ld.Elfstrdat)
 
-				if ld.Debug['v'] != 0 {
-					fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
-				}
-				ld.Dwarfemitdebugsections()
-
 				if ld.Linkmode == ld.LinkExternal {
 					ld.Elfemitreloc()
 				}
@@ -726,7 +713,6 @@ func asmb() {
 			if ld.Debug['v'] != 0 {
 				fmt.Fprintf(&ld.Bso, "%5.2f dwarf\n", obj.Cputime())
 			}
-			ld.Dwarfemitdebugsections()
 
 		case obj.Hdarwin:
 			if ld.Linkmode == ld.LinkExternal {