cmd/link/internal/ld: introduce and use windowsgui variable

cmd/link -H flag is stored in variable of type
cmd/internal/obj.HeadType. The HeadType type from cmd/internal/obj
accepts Hwindows and Hwindowsgui values, but these values have
same meaning - build PE executable, except for 2 places in
cmd/link/internal/ld package.

This CL introduces code to store cmd/link "windowsgui" -H flag
in cmd/link/internal/ld, so cmd/internal/obj.Hwindowsgui can be
removed in the next CL.

This CL also includes 2 changes to code where distinction
between Hwindows and Hwindowsgui is important.

Change-Id: Ie5ee1f374e50c834652a037f2770118d56c21a2a
Reviewed-on: https://go-review.googlesource.com/38760Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1026,9 +1026,11 @@ func (l *Link) hostlink() {
 	case obj.Hopenbsd:
 		argv = append(argv, "-Wl,-nopie")
 	case obj.Hwindows:
-		argv = append(argv, "-mconsole")
-	case obj.Hwindowsgui:
-		argv = append(argv, "-mwindows")
+		if windowsgui {
+			argv = append(argv, "-mwindows")
+		} else {
+			argv = append(argv, "-mconsole")
+		}
 	}
 
 	switch Buildmode {

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

@@ -44,12 +44,12 @@ import (
 
 var (
 	pkglistfornote []byte
+	windowsgui     bool // writes a "GUI binary" instead of a "console binary"
 )
 
 func init() {
 	flag.Var(&Linkmode, "linkmode", "set link `mode`")
 	flag.Var(&Buildmode, "buildmode", "set build `mode`")
-	flag.Var(&Headtype, "H", "set header `type`")
 	flag.Var(&rpath, "r", "set the ELF dynamic linker search `path` to dir1:dir2:...")
 }
 
@@ -88,6 +88,7 @@ var (
 	flagInterpreter = flag.String("I", "", "use `linker` as ELF dynamic linker")
 	FlagDebugTramp  = flag.Int("debugtramp", 0, "debug trampolines")
 
+	flagHeadtype    = flag.String("H", "", "set header `type`")
 	FlagRound       = flag.Int("R", -1, "set address rounding `quantum`")
 	FlagTextAddr    = flag.Int64("T", -1, "set text segment `address`")
 	FlagDataAddr    = flag.Int64("D", -1, "set data segment `address`")
@@ -124,6 +125,18 @@ func Main() {
 
 	obj.Flagparse(usage)
 
+	switch *flagHeadtype {
+	case "":
+	case "windowsgui":
+		Headtype = obj.Hwindows
+		windowsgui = true
+	default:
+		if err := Headtype.Set(*flagHeadtype); err != nil {
+			Errorf(nil, "%v", err)
+			usage()
+		}
+	}
+
 	startProfile()
 	if Buildmode == BuildmodeUnset {
 		Buildmode = BuildmodeExe

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

@@ -1292,7 +1292,7 @@ func Asmbpe(ctxt *Link) {
 	oh.SizeOfImage = uint32(nextsectoff)
 	oh64.SizeOfHeaders = uint32(PEFILEHEADR)
 	oh.SizeOfHeaders = uint32(PEFILEHEADR)
-	if Headtype == obj.Hwindowsgui {
+	if windowsgui {
 		oh64.Subsystem = IMAGE_SUBSYSTEM_WINDOWS_GUI
 		oh.Subsystem = IMAGE_SUBSYSTEM_WINDOWS_GUI
 	} else {