[dev.link] cmd/link: write data sections to heap in Asmb on Wasm

Make Wasm more like other architectures, writing data sections to
heap in Asmb instead of Asmb2. Then we can remove the
copy-on-write logic in applying relocations.

Change-Id: I26d5315ea9fba032fe4bdb9b5c7fe483611c4373
Reviewed-on: https://go-review.googlesource.com/c/go/+/230465
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

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

@@ -684,7 +684,7 @@ func addgotsym2(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s load
 	}
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -682,7 +682,7 @@ func addgotsym2(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s load
 	}
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -830,7 +830,7 @@ func addgotsym2(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s load
 	}
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

src/cmd/link/internal/ld/data2.go

@@ -58,15 +58,6 @@ func relocsym2(target *Target, ldr *loader.Loader, err *ErrorReporter, syms *Arc
 	if len(s.R) == 0 {
 		return
 	}
-	if target.IsWasm() && s.Attr.ReadOnly() {
-		// The symbol's content is backed by read-only memory.
-		// Copy it to writable memory to apply relocations.
-		// Only need to do this on Wasm. On other platforms we
-		// apply relocations to the output buffer, which is
-		// always writeable.
-		s.P = append([]byte(nil), s.P...)
-		// No need to unset AttrReadOnly because it will not be used.
-	}
 	for ri := int32(0); ri < int32(len(s.R)); ri++ {
 		r := &s.R[ri]
 		if r.Done {

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

@@ -265,7 +265,7 @@ type Arch struct {
 	// file. Typically, Asmb writes most of the content (sections and
 	// segments), for which we have computed the size and offset. Asmb2
 	// writes the rest.
-	Asmb  func(*Link)
+	Asmb  func(*Link, *loader.Loader)
 	Asmb2 func(*Link)
 
 	Elfreloc1   func(*Link, *sym.Reloc, int64) bool

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

@@ -325,7 +325,7 @@ func Main(arch *sys.Arch, theArch Arch) {
 	// Asmb will redirect symbols to the output file mmap, and relocations
 	// will be applied directly there.
 	bench.Start("Asmb")
-	thearch.Asmb(ctxt)
+	thearch.Asmb(ctxt, ctxt.loader)
 	bench.Start("reloc")
 	ctxt.reloc()
 	bench.Start("Asmb2")

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

@@ -164,7 +164,7 @@ func archrelocvariant(target *ld.Target, syms *ld.ArchSyms, r *sym.Reloc, s *sym
 	return -1
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -170,7 +170,7 @@ func archrelocvariant(target *ld.Target, syms *ld.ArchSyms, r *sym.Reloc, s *sym
 	return -1
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -1082,7 +1082,7 @@ func ensureglinkresolver2(ctxt *ld.Link, ldr *loader.Loader) *loader.SymbolBuild
 	return glink
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

src/cmd/link/internal/riscv64/asm.go

@@ -98,7 +98,7 @@ func archrelocvariant(target *ld.Target, syms *ld.ArchSyms, r *sym.Reloc, s *sym
 	return -1
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -485,7 +485,7 @@ func addgotsym2(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s load
 	}
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}

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

@@ -92,7 +92,30 @@ func assignAddress(ldr *loader.Loader, sect *sym.Section, n int, s loader.Sym, v
 	return sect, n, va
 }
 
-func asmb(ctxt *ld.Link) {} // dummy
+type wasmDataSect struct {
+	sect *sym.Section
+	data []byte
+}
+
+var dataSects []wasmDataSect
+
+func asmb(ctxt *ld.Link, ldr *loader.Loader) {
+	sections := []*sym.Section{
+		ldr.SymSect(ldr.Lookup("runtime.rodata", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.typelink", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.itablink", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.symtab", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.pclntab", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.noptrdata", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.data", 0)),
+	}
+
+	dataSects = make([]wasmDataSect, len(sections))
+	for i, sect := range sections {
+		data := ld.DatblkBytes(ctxt, int64(sect.Vaddr), int64(sect.Length))
+		dataSects[i] = wasmDataSect{sect, data}
+	}
+}
 
 // asmb writes the final WebAssembly module binary.
 // Spec: https://webassembly.github.io/spec/core/binary/modules.html
@@ -396,16 +419,6 @@ func writeCodeSec(ctxt *ld.Link, fns []*wasmFunc) {
 func writeDataSec(ctxt *ld.Link) {
 	sizeOffset := writeSecHeader(ctxt, sectionData)
 
-	sections := []*sym.Section{
-		ctxt.Syms.Lookup("runtime.rodata", 0).Sect,
-		ctxt.Syms.Lookup("runtime.typelink", 0).Sect,
-		ctxt.Syms.Lookup("runtime.itablink", 0).Sect,
-		ctxt.Syms.Lookup("runtime.symtab", 0).Sect,
-		ctxt.Syms.Lookup("runtime.pclntab", 0).Sect,
-		ctxt.Syms.Lookup("runtime.noptrdata", 0).Sect,
-		ctxt.Syms.Lookup("runtime.data", 0).Sect,
-	}
-
 	type dataSegment struct {
 		offset int32
 		data   []byte
@@ -420,9 +433,9 @@ func writeDataSec(ctxt *ld.Link) {
 	const maxNumSegments = 100000
 
 	var segments []*dataSegment
-	for secIndex, sec := range sections {
+	for secIndex, ds := range dataSects {
-		data := ld.DatblkBytes(ctxt, int64(sec.Vaddr), int64(sec.Length))
+		data := ds.data
-		offset := int32(sec.Vaddr)
+		offset := int32(ds.sect.Vaddr)
 
 		// skip leading zeroes
 		for len(data) > 0 && data[0] == 0 {
@@ -433,7 +446,7 @@ func writeDataSec(ctxt *ld.Link) {
 		for len(data) > 0 {
 			dataLen := int32(len(data))
 			var segmentEnd, zeroEnd int32
-			if len(segments)+(len(sections)-secIndex) == maxNumSegments {
+			if len(segments)+(len(dataSects)-secIndex) == maxNumSegments {
 				segmentEnd = dataLen
 				zeroEnd = dataLen
 			} else {

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

@@ -564,7 +564,7 @@ func addgotsym2(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s load
 	}
 }
 
-func asmb(ctxt *ld.Link) {
+func asmb(ctxt *ld.Link, _ *loader.Loader) {
 	if ctxt.IsELF {
 		ld.Asmbelfsetup()
 	}