cmd/link: process data symbols with slices

First (and largest single) step to switching cmd/link from linked
lists of symbols to slices.

Sort sections independently and concurrently.
This reduces jujud link times on linux/amd64 by ~4%.

Updates #15374

Change-Id: I452bc8f33081039468636502fe3c1cc8d6ed9efa
Reviewed-on: https://go-review.googlesource.com/22205Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

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

@@ -1670,7 +1670,7 @@ func elfshreloc(sect *Section) *ElfShdr {
 	return sh
 }
 
-func elfrelocsect(sect *Section, first *LSym) {
+func elfrelocsect(sect *Section, syms []*LSym) {
 	// If main section is SHT_NOBITS, nothing to relocate.
 	// Also nothing to relocate in .shstrtab.
 	if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
@@ -1681,18 +1681,18 @@ func elfrelocsect(sect *Section, first *LSym) {
 	}
 
 	sect.Reloff = uint64(Cpos())
-	var sym *LSym
-	for sym = first; sym != nil; sym = sym.Next {
-		if !sym.Attr.Reachable() {
+	for i, s := range syms {
+		if !s.Attr.Reachable() {
 			continue
 		}
-		if uint64(sym.Value) >= sect.Vaddr {
+		if uint64(s.Value) >= sect.Vaddr {
+			syms = syms[i:]
 			break
 		}
 	}
 
 	eaddr := int32(sect.Vaddr + sect.Length)
-	for ; sym != nil; sym = sym.Next {
+	for _, sym := range syms {
 		if !sym.Attr.Reachable() {
 			continue
 		}
@@ -1710,7 +1710,6 @@ func elfrelocsect(sect *Section, first *LSym) {
 				Diag("missing xsym in relocation")
 				continue
 			}
-
 			if r.Xsym.ElfsymForReloc() == 0 {
 				Diag("reloc %d to non-elf symbol %s (outer=%s) %d", r.Type, r.Sym.Name, r.Xsym.Name, r.Sym.Type)
 			}
@@ -1728,7 +1727,7 @@ func Elfemitreloc() {
 		Cput(0)
 	}
 
-	elfrelocsect(Segtext.Sect, Ctxt.Textp)
+	elfrelocsect(Segtext.Sect, list2slice(Ctxt.Textp))
 	for sect := Segtext.Sect.Next; sect != nil; sect = sect.Next {
 		elfrelocsect(sect, datap)
 	}
@@ -1739,7 +1738,7 @@ func Elfemitreloc() {
 		elfrelocsect(sect, datap)
 	}
 	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
-		elfrelocsect(sect, dwarfp)
+		elfrelocsect(sect, list2slice(dwarfp))
 	}
 }
 

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

@@ -130,7 +130,6 @@ func (r *Rpath) String() string {
 
 var (
 	Thearch Arch
-	datap   *LSym
 	Debug   [128]int
 	Lcsize  int32
 	rpath   Rpath
@@ -2109,7 +2108,7 @@ func undef() {
 	for s := Ctxt.Textp; s != nil; s = s.Next {
 		undefsym(s)
 	}
-	for s := datap; s != nil; s = s.Next {
+	for _, s := range datap {
 		undefsym(s)
 	}
 	if nerrors > 0 {

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

@@ -806,25 +806,25 @@ func Domacholink() int64 {
 	return Rnd(int64(size), int64(INITRND))
 }
 
-func machorelocsect(sect *Section, first *LSym) {
+func machorelocsect(sect *Section, syms []*LSym) {
 	// If main section has no bits, nothing to relocate.
 	if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
 		return
 	}
 
 	sect.Reloff = uint64(Cpos())
-	var sym *LSym
-	for sym = first; sym != nil; sym = sym.Next {
-		if !sym.Attr.Reachable() {
+	for i, s := range syms {
+		if !s.Attr.Reachable() {
 			continue
 		}
-		if uint64(sym.Value) >= sect.Vaddr {
+		if uint64(s.Value) >= sect.Vaddr {
+			syms = syms[i:]
 			break
 		}
 	}
 
 	eaddr := int32(sect.Vaddr + sect.Length)
-	for ; sym != nil; sym = sym.Next {
+	for _, sym := range syms {
 		if !sym.Attr.Reachable() {
 			continue
 		}
@@ -852,7 +852,7 @@ func Machoemitreloc() {
 		Cput(0)
 	}
 
-	machorelocsect(Segtext.Sect, Ctxt.Textp)
+	machorelocsect(Segtext.Sect, list2slice(Ctxt.Textp))
 	for sect := Segtext.Sect.Next; sect != nil; sect = sect.Next {
 		machorelocsect(sect, datap)
 	}
@@ -860,6 +860,6 @@ func Machoemitreloc() {
 		machorelocsect(sect, datap)
 	}
 	for sect := Segdwarf.Sect; sect != nil; sect = sect.Next {
-		machorelocsect(sect, dwarfp)
+		machorelocsect(sect, list2slice(dwarfp))
 	}
 }

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

@@ -764,7 +764,7 @@ func addexports() {
 
 // perelocsect relocates symbols from first in section sect, and returns
 // the total number of relocations emitted.
-func perelocsect(sect *Section, first *LSym) int {
+func perelocsect(sect *Section, syms []*LSym) int {
 	// If main section has no bits, nothing to relocate.
 	if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
 		return 0
@@ -773,18 +773,18 @@ func perelocsect(sect *Section, first *LSym) int {
 	relocs := 0
 
 	sect.Reloff = uint64(Cpos())
-	var sym *LSym
-	for sym = first; sym != nil; sym = sym.Next {
-		if !sym.Attr.Reachable() {
+	for i, s := range syms {
+		if !s.Attr.Reachable() {
 			continue
 		}
-		if uint64(sym.Value) >= sect.Vaddr {
+		if uint64(s.Value) >= sect.Vaddr {
+			syms = syms[i:]
 			break
 		}
 	}
 
 	eaddr := int32(sect.Vaddr + sect.Length)
-	for ; sym != nil; sym = sym.Next {
+	for _, sym := range syms {
 		if !sym.Attr.Reachable() {
 			continue
 		}
@@ -831,7 +831,7 @@ func peemitreloc(text, data, ctors *IMAGE_SECTION_HEADER) {
 	Lputl(0)
 	Wputl(0)
 
-	n := perelocsect(Segtext.Sect, Ctxt.Textp) + 1
+	n := perelocsect(Segtext.Sect, list2slice(Ctxt.Textp)) + 1
 	for sect := Segtext.Sect.Next; sect != nil; sect = sect.Next {
 		n += perelocsect(sect, datap)
 	}