cmd/internal/obj: simplify filename handling

The old Go object file format used linker symbols like "gofile..foo"
to record references to the filename "foo". But the current object
file format has a dedicated section for file names, so we don't need
these useless prefixes anymore.

Also, change DWARF generation to pass around the src.Pos directly,
rather than the old file symbols, which it just turned back into a
file index before writing out anyway.

Finally, directly record the FileIndex into src.PosBase, so that we
can skip the map lookups.

Change-Id: Ia4a5ebfa95da271f2522e45befdb9f137c16d373
Reviewed-on: https://go-review.googlesource.com/c/go/+/523378
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

1 files changed, 10 insertions, 13 deletions

diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index 86bc9e6823..c48b576fa0 100644
--- a/src/cmd/internal/dwarf/dwarf.go
+++ b/src/cmd/internal/dwarf/dwarf.go
@@ -9,6 +9,7 @@ package dwarf
 
 import (
 	"bytes"
+	"cmd/internal/src"
 	"errors"
 	"fmt"
 	"internal/buildcfg"
@@ -85,13 +86,12 @@ type Range struct {
 type FnState struct {
 	Name          string
 	Info          Sym
-	Filesym       Sym
 	Loc           Sym
 	Ranges        Sym
 	Absfn         Sym
 	StartPC       Sym
+	StartPos      src.Pos
 	Size          int64
-	StartLine     int32
 	External      bool
 	Scopes        []Scope
 	InlCalls      InlCalls
@@ -166,11 +166,8 @@ type InlCall struct {
 	// index into ctx.InlTree describing the call inlined here
 	InlIndex int
 
-	// Symbol of file containing inlined call site (really *obj.LSym).
-	CallFile Sym
-
-	// Line number of inlined call site.
-	CallLine uint32
+	// Position of the inlined call site.
+	CallPos src.Pos
 
 	// Dwarf abstract subroutine symbol (really *obj.LSym).
 	AbsFunSym Sym
@@ -202,7 +199,6 @@ type Context interface {
 	RecordDclReference(from Sym, to Sym, dclIdx int, inlIndex int)
 	RecordChildDieOffsets(s Sym, vars []*Var, offsets []int32)
 	AddString(s Sym, v string)
-	AddFileRef(s Sym, f interface{})
 	Logf(format string, args ...interface{})
 }
 
@@ -1246,7 +1242,8 @@ func PutAbstractFunc(ctxt Context, s *FnState) error {
 	// DW_AT_inlined value
 	putattr(ctxt, s.Absfn, abbrev, DW_FORM_data1, DW_CLS_CONSTANT, int64(DW_INL_inlined), nil)
 
-	putattr(ctxt, s.Absfn, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartLine), nil)
+	// TODO(mdempsky): Shouldn't we write out StartPos.FileIndex() too?
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
 
 	var ev int64
 	if s.External {
@@ -1335,9 +1332,9 @@ func putInlinedFunc(ctxt Context, s *FnState, callIdx int) error {
 	}
 
 	// Emit call file, line attrs.
-	ctxt.AddFileRef(s.Info, ic.CallFile)
+	putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, int64(1+ic.CallPos.FileIndex()), nil) // 1-based file table
 	form := int(expandPseudoForm(DW_FORM_udata_pseudo))
-	putattr(ctxt, s.Info, abbrev, form, DW_CLS_CONSTANT, int64(ic.CallLine), nil)
+	putattr(ctxt, s.Info, abbrev, form, DW_CLS_CONSTANT, int64(ic.CallPos.RelLine()), nil)
 
 	// Variables associated with this inlined routine instance.
 	vars := ic.InlVars
@@ -1438,8 +1435,8 @@ func PutDefaultFunc(ctxt Context, s *FnState, isWrapper bool) error {
 	if isWrapper {
 		putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, int64(1), 0)
 	} else {
-		ctxt.AddFileRef(s.Info, s.Filesym)
-		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartLine), nil)
+		putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, int64(1+s.StartPos.FileIndex()), nil) // 1-based file index
+		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
 
 		var ev int64
 		if s.External {