cmd/link: move dwarf part of DWARF generation before type name mangling

Splits part of dwarfgeneratedebugsyms into a new function,
dwarfGenerateDebugInfo which is called between deadcode elimination
and type name mangling.
This function takes care of collecting and processing the DIEs for
all functions and package-level variables and also generates DIEs
for all types used in the program.

Fixes #23733

Change-Id: I75ef0608fbed2dffc3be7a477f1b03e7e740ec61
Reviewed-on: https://go-review.googlesource.com/111237
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

misc/cgo/testplugin/src/checkdwarf/main.go

+// Copyright 2018 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.
+
+// Usage:
+//
+//  checkdwarf <exe> <suffix>
+//
+// Opens <exe>, which must be an executable or a library and checks that
+// there is an entry in .debug_info whose name ends in <suffix>
+
+package main
+
+import (
+	"debug/dwarf"
+	"debug/elf"
+	"debug/macho"
+	"debug/pe"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "checkdwarf executable-or-library DIE-suffix\n")
+}
+
+type dwarfer interface {
+	DWARF() (*dwarf.Data, error)
+}
+
+func openElf(path string) dwarfer {
+	exe, err := elf.Open(path)
+	if err != nil {
+		return nil
+	}
+	return exe
+}
+
+func openMacho(path string) dwarfer {
+	exe, err := macho.Open(path)
+	if err != nil {
+		return nil
+	}
+	return exe
+}
+
+func openPE(path string) dwarfer {
+	exe, err := pe.Open(path)
+	if err != nil {
+		return nil
+	}
+	return exe
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		usage()
+	}
+
+	exePath := os.Args[1]
+	dieSuffix := os.Args[2]
+
+	var exe dwarfer
+
+	for _, openfn := range []func(string) dwarfer{openMacho, openPE, openElf} {
+		exe = openfn(exePath)
+		if exe != nil {
+			break
+		}
+	}
+
+	if exe == nil {
+		fmt.Fprintf(os.Stderr, "could not open %s", exePath)
+		os.Exit(1)
+	}
+
+	data, err := exe.DWARF()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error opening DWARF: %v", err)
+		os.Exit(1)
+	}
+
+	rdr := data.Reader()
+	for {
+		e, err := rdr.Next()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "error reading DWARF: %v", err)
+			os.Exit(1)
+		}
+		if e == nil {
+			break
+		}
+		name, hasname := e.Val(dwarf.AttrName).(string)
+		if !hasname {
+			continue
+		}
+		if strings.HasSuffix(name, dieSuffix) {
+			// found
+			os.Exit(0)
+		}
+	}
+
+	fmt.Fprintf(os.Stderr, "no entry with a name ending in %q was found", dieSuffix)
+	os.Exit(1)
+}

misc/cgo/testplugin/test.bash

@@ -32,6 +32,10 @@ GOPATH=$(pwd) go build -gcflags "$GO_GCFLAGS" -buildmode=plugin -o=unnamed1.so u
 GOPATH=$(pwd) go build -gcflags "$GO_GCFLAGS" -buildmode=plugin -o=unnamed2.so unnamed2/main.go
 GOPATH=$(pwd) go build -gcflags "$GO_GCFLAGS" host
 
+# test that DWARF sections are emitted for plugins and programs importing "plugin"
+go run src/checkdwarf/main.go plugin2.so plugin2.UnexportedNameReuse
+go run src/checkdwarf/main.go host main.main
+
 LD_LIBRARY_PATH=$(pwd) ./host
 
 # Test that types and itabs get properly uniqified.

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

@@ -1602,7 +1602,7 @@ func (ctxt *Link) dodata() {
 		datap = append(datap, data[symn]...)
 	}
 
-	dwarfgeneratedebugsyms(ctxt)
+	dwarfGenerateDebugSyms(ctxt)
 
 	var i int
 	for ; i < len(dwarfp); i++ {

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

@@ -654,7 +654,6 @@ func (ctxt *Link) mangleTypeSym() {
 		return
 	}
 
-	*FlagW = true // disable DWARF generation
 	for _, s := range ctxt.Syms.Allsym {
 		newName := typeSymbolMangle(s.Name)
 		if newName != s.Name {

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

@@ -89,6 +89,9 @@ type Link struct {
 
 	// Used to implement field tracking.
 	Reachparent map[*sym.Symbol]*sym.Symbol
+
+	compUnits         []*compilationUnit // DWARF compilation units
+	compUnitByPackage map[*sym.Library]*compilationUnit
 }
 
 type unresolvedSymKey struct {

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

@@ -208,6 +208,7 @@ func Main(arch *sys.Arch, theArch Arch) {
 
 	ctxt.dostrdata()
 	deadcode(ctxt)
+	dwarfGenerateDebugInfo(ctxt)
 	if objabi.Fieldtrack_enabled != 0 {
 		fieldtrack(ctxt)
 	}

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

@@ -318,6 +318,8 @@ overwrite:
 			pc.InlTree[i].Func = r.readSymIndex()
 		}
 
+		s.FuncInfo.IsStmtSym = r.syms.Lookup(dwarf.IsStmtPrefix+s.Name, int(s.Version))
+
 		s.Lib = r.lib
 		if !dupok {
 			if s.Attr.OnList() {

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

@@ -478,6 +478,7 @@ type FuncInfo struct {
 	Pcline      Pcdata
 	Pcinline    Pcdata
 	Pcdata      []Pcdata
+	IsStmtSym   *Symbol
 	Funcdata    []*Symbol
 	Funcdataoff []int64
 	File        []*Symbol