[dev.link] cmd/link, cmd/internal/goobj2: adopt new DWARF compilation unit...

[dev.link] cmd/link, cmd/internal/goobj2: adopt new DWARF compilation unit logic with new object file

The dev.link branch was not sync'd with the new DWARF compilation
unit logic change on the master branch, and the new object file
format didn't support this.

This CL adds the new DWARF CU and file table support to the new
object file format. In the old object file, the DWARF file table
is a separate section. For now, we do the same with the new
object file, keeping it as a separate block.

While here, also refactor the loader code so it is easier for the
loader to carry per-object informations.

Change-Id: I4c317941fc0a5831acbc11ce8c2a8b7421471372
Reviewed-on: https://go-review.googlesource.com/c/go/+/198198Reviewed-by: Austin Clements <austin@google.com>

src/cmd/internal/goobj2/objfile.go

@@ -31,6 +31,8 @@ import (
 //
 //    PkgIndex [...]stringOff // TODO: add fingerprints
 //
+//    DwarfFiles [...]stringOff // XXX as a separate block for now
+//
 //    SymbolDefs [...]struct {
 //       Name stringOff
 //       ABI  uint16
@@ -126,6 +128,7 @@ const (
 // Blocks
 const (
 	BlkPkgIdx = iota
+	BlkDwarfFile
 	BlkSymdef
 	BlkNonpkgdef
 	BlkNonpkgref
@@ -471,6 +474,24 @@ func (r *Reader) Pkglist() []string {
 	return s
 }
 
+func (r *Reader) NPkg() int {
+	return int(r.h.Offsets[BlkPkgIdx+1]-r.h.Offsets[BlkPkgIdx]) / 4
+}
+
+func (r *Reader) Pkg(i int) string {
+	off := r.h.Offsets[BlkPkgIdx] + uint32(i)*4
+	return r.StringRef(off)
+}
+
+func (r *Reader) NDwarfFile() int {
+	return int(r.h.Offsets[BlkDwarfFile+1]-r.h.Offsets[BlkDwarfFile]) / 4
+}
+
+func (r *Reader) DwarfFile(i int) string {
+	off := r.h.Offsets[BlkDwarfFile] + uint32(i)*4
+	return r.StringRef(off)
+}
+
 func (r *Reader) NSym() int {
 	symsiz := (&Sym{}).Size()
 	return int(r.h.Offsets[BlkSymdef+1]-r.h.Offsets[BlkSymdef]) / symsiz
@@ -531,6 +552,11 @@ func (r *Reader) DataSize(i int) int {
 	return int(r.DataOff(i+1) - r.DataOff(i))
 }
 
+// Data returns the i-th symbol's data.
+func (r *Reader) Data(i int) []byte {
+	return r.BytesAt(r.DataOff(i), r.DataSize(i))
+}
+
 // AuxDataBase returns the base offset of the aux data block.
 func (r *Reader) PcdataBase() uint32 {
 	return r.h.Offsets[BlkPcdata]

src/cmd/internal/obj/objfile2.go

@@ -42,6 +42,12 @@ func WriteObjFile2(ctxt *Link, b *bio.Writer, pkgpath string) {
 		w.StringRef(pkg)
 	}
 
+	// DWARF file table
+	h.Offsets[goobj2.BlkDwarfFile] = w.Offset()
+	for _, f := range ctxt.PosTable.DebugLinesFileTable() {
+		w.StringRef(f)
+	}
+
 	// Symbol definitions
 	h.Offsets[goobj2.BlkSymdef] = w.Offset()
 	for _, s := range ctxt.defs {
@@ -198,6 +204,9 @@ func (w *writer) StringTable() {
 			w.AddString(f)
 		}
 	})
+	for _, f := range w.ctxt.PosTable.DebugLinesFileTable() {
+		w.AddString(f)
+	}
 }
 
 func (w *writer) Sym(s *LSym) {

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

@@ -403,11 +403,7 @@ func (ctxt *Link) loadlib() {
 
 	if *flagNewobj {
 		// Add references of externally defined symbols.
-		for _, lib := range ctxt.Library {
-			for _, r := range lib.Readers {
-				objfile.LoadRefs(ctxt.loader, r.Reader, lib, ctxt.Arch, ctxt.Syms, r.Version)
-			}
-		}
+		objfile.LoadRefs(ctxt.loader, ctxt.Arch, ctxt.Syms)
 
 		// Load cgo directives.
 		for _, p := range ctxt.cgodata {
@@ -550,11 +546,7 @@ func (ctxt *Link) loadlib() {
 
 	// For now, load relocations for dead-code elimination.
 	if *flagNewobj {
-		for _, lib := range ctxt.Library {
-			for _, r := range lib.Readers {
-				objfile.LoadReloc(ctxt.loader, r.Reader, lib, r.Version, ctxt.LibraryByPkg)
-			}
-		}
+		objfile.LoadReloc(ctxt.loader)
 	}
 }
 
@@ -2545,11 +2537,7 @@ func dfs(lib *sym.Library, mark map[*sym.Library]markKind, order *[]*sym.Library
 
 func (ctxt *Link) loadlibfull() {
 	// Load full symbol contents, resolve indexed references.
-	for _, lib := range ctxt.Library {
-		for _, r := range lib.Readers {
-			objfile.LoadFull(ctxt.loader, r.Reader, lib, r.Version, ctxt.LibraryByPkg)
-		}
-	}
+	objfile.LoadFull(ctxt.loader)
 
 	// For now, add all symbols to ctxt.Syms.
 	for _, s := range ctxt.loader.Syms {
@@ -2557,6 +2545,9 @@ func (ctxt *Link) loadlibfull() {
 			ctxt.Syms.Add(s)
 		}
 	}
+
+	// Drop the reference.
+	ctxt.loader = nil
 }
 
 func (ctxt *Link) dumpsyms() {

src/cmd/link/internal/sym/library.go

@@ -4,8 +4,6 @@
 
 package sym
 
-import "cmd/internal/goobj2"
-
 type Library struct {
 	Objref        string
 	Srcref        string
@@ -20,11 +18,6 @@ type Library struct {
 	Main          bool
 	Safe          bool
 	Units         []*CompilationUnit
-
-	Readers []struct { // TODO: probably move this to Loader
-		Reader  *goobj2.Reader
-		Version int
-	}
 }
 
 func (l Library) String() string {