cmd: generate DWARF for functions in compile instead of link.

This is a copy of golang.org/cl/22092 by Ryan Brown.

Here's his original comment:
On my machine this increases the average time for 'go build cmd/go' from
2.25s to 2.36s. I tried to measure compile and link separately but saw
no significant change.

Change-Id: If0d2b756d52a0d30d4eda526929c82794d89dd7b
Reviewed-on: https://go-review.googlesource.com/25311
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/buildtool.go

@@ -41,6 +41,7 @@ var bootstrapDirs = []string{
 	"compile/internal/s390x",
 	"internal/bio",
 	"internal/gcprog",
+	"internal/dwarf",
 	"internal/obj",
 	"internal/obj/arm",
 	"internal/obj/arm64",

src/cmd/link/internal/ld/dwarf_defs.go → src/cmd/internal/dwarf/dwarf_defs.go

@@ -2,40 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package ld
-
-// TODO/NICETOHAVE:
-//   - eliminate DW_CLS_ if not used
-//   - package info in compilation units
-//   - assign global variables and types to their packages
-//   - gdb uses c syntax, meaning clumsy quoting is needed for go identifiers. eg
-//     ptype struct '[]uint8' and qualifiers need to be quoted away
-//   - lexical scoping is lost, so gdb gets confused as to which 'obj.i' you mean.
-//   - file:line info for variables
-//   - make strings a typedef so prettyprinters can see the underlying string type
-//
-// Copyright 2010 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-/*
- * Emit debug_abbrevs, debug_info and debug_line sections to current
- * offset in cout.
- */
-
-/*
- * Add the dwarf section names to the ELF
- * s[ection]h[eader]str[ing]tab.  Prerequisite for
- * dwarfaddelfheaders().
- */
-
-/*
- * Add section headers pointing to the sections emitted in
- * dwarfemitdebugsections.
- */
-// Copyright 2010 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+package dwarf
 
 // Cut, pasted, tr-and-awk'ed from tables in
 // http://dwarfstd.org/doc/Dwarf3.pdf

src/cmd/internal/obj/objfile.go

@@ -109,6 +109,7 @@ package obj
 
 import (
 	"bufio"
+	"cmd/internal/dwarf"
 	"cmd/internal/sys"
 	"fmt"
 	"log"
@@ -506,3 +507,94 @@ type relocByOff []Reloc
 func (x relocByOff) Len() int           { return len(x) }
 func (x relocByOff) Less(i, j int) bool { return x[i].Off < x[j].Off }
 func (x relocByOff) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
+
+// implement dwarf.Context
+type dwCtxt struct{ *Link }
+
+func (c dwCtxt) PtrSize() int {
+	return c.Arch.PtrSize
+}
+func (c dwCtxt) AddInt(s dwarf.Sym, size int, i int64) {
+	ls := s.(*LSym)
+	ls.WriteInt(c.Link, ls.Size, size, i)
+}
+func (c dwCtxt) AddBytes(s dwarf.Sym, b []byte) {
+	ls := s.(*LSym)
+	ls.WriteBytes(c.Link, ls.Size, b)
+}
+func (c dwCtxt) AddString(s dwarf.Sym, v string) {
+	ls := s.(*LSym)
+	ls.WriteString(c.Link, ls.Size, len(v), v)
+	ls.WriteInt(c.Link, ls.Size, 1, 0)
+}
+func (c dwCtxt) SymValue(s dwarf.Sym) int64 {
+	return 0
+}
+func (c dwCtxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
+	rsym := data.(*LSym)
+	ls := s.(*LSym)
+	size := c.PtrSize()
+	ls.WriteAddr(c.Link, ls.Size, size, rsym, value)
+}
+func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
+	ls := s.(*LSym)
+	rsym := t.(*LSym)
+	ls.WriteAddr(c.Link, ls.Size, size, rsym, ofs)
+	r := &ls.R[len(ls.R)-1]
+	r.Type = R_DWARFREF
+}
+
+func gendwarf(ctxt *Link, text []*LSym) []*LSym {
+	dctxt := dwCtxt{ctxt}
+	var dw []*LSym
+
+	for _, s := range text {
+		dsym := Linklookup(ctxt, dwarf.InfoPrefix+s.Name, int(s.Version))
+		if dsym.Size != 0 {
+			continue
+		}
+		dw = append(dw, dsym)
+		dsym.Type = SDWARFINFO
+		dsym.Dupok = s.Dupok
+		var vars dwarf.Var
+		var abbrev int
+		var offs int32
+		for a := s.Autom; a != nil; a = a.Link {
+			switch a.Name {
+			case NAME_AUTO:
+				abbrev = dwarf.DW_ABRV_AUTO
+				offs = a.Aoffset
+				if ctxt.FixedFrameSize() == 0 {
+					offs -= int32(ctxt.Arch.PtrSize)
+				}
+				if Framepointer_enabled(Getgoos(), Getgoarch()) {
+					offs -= int32(ctxt.Arch.PtrSize)
+				}
+
+			case NAME_PARAM:
+				abbrev = dwarf.DW_ABRV_PARAM
+				offs = a.Aoffset + int32(ctxt.FixedFrameSize())
+
+			default:
+				continue
+			}
+			typename := dwarf.InfoPrefix + a.Gotype.Name[len("type."):]
+			dwvar := &dwarf.Var{
+				Name:   a.Asym.Name,
+				Abbrev: abbrev,
+				Offset: int32(offs),
+				Type:   Linklookup(ctxt, typename, 0),
+			}
+			dws := &vars.Link
+			for ; *dws != nil; dws = &(*dws).Link {
+				if offs <= (*dws).Offset {
+					break
+				}
+			}
+			dwvar.Link = *dws
+			*dws = dwvar
+		}
+		dwarf.PutFunc(dctxt, dsym, s.Name, s.Version == 0, s, s.Size, vars.Link)
+	}
+	return dw
+}

src/cmd/internal/obj/plist.go

@@ -209,6 +209,7 @@ func flushplist(ctxt *Link, freeProgs bool) {
 
 	// Add to running list in ctxt.
 	ctxt.Text = append(ctxt.Text, text...)
+	ctxt.Data = append(ctxt.Data, gendwarf(ctxt, text)...)
 	ctxt.Plist = nil
 	ctxt.Plast = nil
 	ctxt.Curp = nil

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

@@ -342,8 +342,14 @@ func relocsym(s *LSym) {
 		if r.Sym != nil && (r.Sym.Type&(obj.SMASK|obj.SHIDDEN) == 0 || r.Sym.Type&obj.SMASK == obj.SXREF) {
 			// When putting the runtime but not main into a shared library
 			// these symbols are undefined and that's OK.
-			if Buildmode == BuildmodeShared && (r.Sym.Name == "main.main" || r.Sym.Name == "main.init") {
+			if Buildmode == BuildmodeShared {
+				if r.Sym.Name == "main.main" || r.Sym.Name == "main.init" {
 					r.Sym.Type = obj.SDYNIMPORT
+				} else if strings.HasPrefix(r.Sym.Name, "go.info.") {
+					// Skip go.info symbols. They are only needed to communicate
+					// DWARF info between the compiler and linker.
+					continue
+				}
 			} else {
 				Diag("%s: not defined", r.Sym.Name)
 				continue

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

@@ -111,6 +111,7 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/internal/bio"
+	"cmd/internal/dwarf"
 	"cmd/internal/obj"
 	"crypto/sha1"
 	"encoding/base64"
@@ -401,6 +402,37 @@ overwrite:
 			r.ctxt.Textp = append(r.ctxt.Textp, s)
 		}
 	}
+	if s.Type == obj.SDWARFINFO {
+		r.patchDWARFName(s)
+	}
+}
+
+func (r *objReader) patchDWARFName(s *LSym) {
+	// This is kind of ugly. Really the package name should not
+	// even be included here.
+	if s.Size < 1 || s.P[0] != dwarf.DW_ABRV_FUNCTION {
+		return
+	}
+	e := bytes.IndexByte(s.P, 0)
+	if e == -1 {
+		return
+	}
+	p := bytes.Index(s.P[:e], emptyPkg)
+	if p == -1 {
+		return
+	}
+	pkgprefix := []byte(r.pkg + ".")
+	patched := bytes.Replace(s.P[:e], emptyPkg, pkgprefix, -1)
+
+	s.P = append(patched, s.P[e:]...)
+	delta := int64(len(s.P)) - s.Size
+	s.Size = int64(len(s.P))
+	for i := range s.R {
+		r := &s.R[i]
+		if r.Off > int32(e) {
+			r.Off += int32(delta)
+		}
+	}
 }
 
 func (r *objReader) readFull(b []byte) {

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

@@ -269,6 +269,8 @@ func Asmplan9sym() {
 
 var symt *LSym
 
+var encbuf [10]byte
+
 func Wputb(w uint16) { Cwrite(Append16b(encbuf[:0], w)) }
 func Lputb(l uint32) { Cwrite(Append32b(encbuf[:0], l)) }
 func Vputb(v uint64) { Cwrite(Append64b(encbuf[:0], v)) }