cmd/compile: update object file format for DWARF file table

In CL 188317, we generate the debug_lines in the compiler, and created a
new symbol to hold the line table. Here we modify the object file format
to output the file table.

Change-Id: Ibee192e80b86ff6af36467a0b1c26ee747dfee37
Reviewed-on: https://go-review.googlesource.com/c/go/+/191167
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

2 files changed, 9 insertions, 31 deletions

diff --git a/src/cmd/internal/obj/dwarf.go b/src/cmd/internal/obj/dwarf.go
index ebe69f8811..23c668c5a9 100644
--- a/src/cmd/internal/obj/dwarf.go
+++ b/src/cmd/internal/obj/dwarf.go
@@ -235,15 +235,3 @@ func putpclcdelta(linkctxt *Link, dctxt dwCtxt, s *LSym, deltaPC uint64, deltaLC
 	// Output the special opcode.
 	dctxt.AddUint8(s, uint8(opcode))
 }
-
-// createDebugLinesFileTable creates a new symbol holding the list of files
-// in our package.
-func (ctxt *Link) createDebugLinesFileTable() {
-	dctxt := dwCtxt{ctxt}
-
-	fileLUT := ctxt.PosTable.DebugLinesFileTable()
-	s := ctxt.dwarfFileTableSymbol()
-	for _, file := range fileLUT {
-		dctxt.AddString(s, file)
-	}
-}
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 863989c473..a40c6d8c29 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -86,7 +86,7 @@ func WriteObjFile(ctxt *Link, b *bufio.Writer, pkgpath string) {
 	w := newObjWriter(ctxt, b, pkgpath)
 
 	// Magic header
-	w.wr.WriteString("\x00go112ld")
+	w.wr.WriteString("\x00go114ld")
 
 	// Version
 	w.wr.WriteByte(1)
@@ -97,6 +97,13 @@ func WriteObjFile(ctxt *Link, b *bufio.Writer, pkgpath string) {
 	}
 	w.writeString("")
 
+	// DWARF File Table
+	fileTable := ctxt.PosTable.DebugLinesFileTable()
+	w.writeInt(int64(len(fileTable)))
+	for _, str := range fileTable {
+		w.writeString(str)
+	}
+
 	// Symbol references
 	for _, s := range ctxt.Text {
 		w.writeRefs(s)
@@ -161,7 +168,7 @@ func WriteObjFile(ctxt *Link, b *bufio.Writer, pkgpath string) {
 	}
 
 	// Magic footer
-	w.wr.WriteString("\xffgo112ld")
+	w.wr.WriteString("\xffgo114ld")
 }
 
 // Symbols are prefixed so their content doesn't get confused with the magic footer.
@@ -641,23 +648,6 @@ func (ctxt *Link) DwarfIntConst(myimportpath, name, typename string, val int64)
 	dwarf.PutIntConst(dwCtxt{ctxt}, s, ctxt.Lookup(dwarf.InfoPrefix+typename), myimportpath+"."+name, val)
 }
 
-// dwarfFileTableSymbol creates (or finds) the symbol for holding the line table for this package.
-//
-// The symbol WILL NOT be unique at the per package/archive level. For example,
-// when writing a package archive, we'll write this symbol for the Go code, and
-// one for each assembly file in the package. As such, we can't treat this
-// symbol the same when we read in the object files in the linker. This symbol
-// won't make it to the symbol table, and compilation units will keep track of
-// it.
-// TODO: Actually save this to the object file, and read it back in the linker.
-func (ctxt *Link) dwarfFileTableSymbol() *LSym {
-	s := ctxt.LookupInit(dwarf.DebugLinesPrefix+".package", func(s *LSym) {
-		s.Type = objabi.SDWARFLINES
-		//ctxt.Data = append(ctxt.Data, s)
-	})
-	return s
-}
-
 func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym, myimportpath string) {
 	absfn := ctxt.DwFixups.AbsFuncDwarfSym(s)
 	if absfn.Size != 0 {