cmd/dist,cmd/go: broaden use of asm macro GOEXPERIMENT_REGABI

This extends a change made in https://golang.org/cl/252258 to the go
command (to define an asm macro when GOEXPERIMENT=regabi is in
effect); we need this same macro during the bootstrap build in order
to build the runtime correctly.

In addition, expand the set of packages where the macro is applied to
{runtime, reflect, syscall, runtime/internal/*}, and move the logic
for deciding when something is a "runtime package" out of the
assembler and into cmd/{go,dist}, introducing a new assembler command
line flag instead.

Updates #27539, #40724.

Change-Id: Ifcc7f029f56873584de1e543c55b0d3e54ad6c49
Reviewed-on: https://go-review.googlesource.com/c/go/+/262317
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/asm/internal/flags/flags.go

@@ -24,6 +24,7 @@ var (
 	SymABIs          = flag.Bool("gensymabis", false, "write symbol ABI information to output file, don't assemble")
 	Importpath       = flag.String("p", "", "set expected package import to path")
 	Spectre          = flag.String("spectre", "", "enable spectre mitigations in `list` (all, ret)")
+	CompilingRuntime = flag.Bool("compilingRuntime", false, "source to be compiled is part of the Go runtime")
 )
 
 var (

src/cmd/asm/main.go

@@ -52,7 +52,6 @@ func main() {
 	case "all", "ret":
 		ctxt.Retpoline = true
 	}
-	compilingRuntime := objabi.IsRuntimePackagePath(*flags.Importpath)
 
 	ctxt.Bso = bufio.NewWriter(os.Stdout)
 	defer ctxt.Bso.Flush()
@@ -75,7 +74,8 @@ func main() {
 	var failedFile string
 	for _, f := range flag.Args() {
 		lexer := lex.NewLexer(f)
-		parser := asm.NewParser(ctxt, architecture, lexer, compilingRuntime)
+		parser := asm.NewParser(ctxt, architecture, lexer,
+			*flags.CompilingRuntime)
 		ctxt.DiagFunc = func(format string, args ...interface{}) {
 			diag = true
 			log.Printf(format, args...)

src/cmd/dist/build.go

@@ -832,6 +832,21 @@ func runInstall(pkg string, ch chan struct{}) {
 		asmArgs = append(asmArgs, "-D", "GOMIPS64_"+gomips64)
 	}
 	goasmh := pathf("%s/go_asm.h", workdir)
+	if IsRuntimePackagePath(pkg) {
+		asmArgs = append(asmArgs, "-compilingRuntime")
+		if os.Getenv("GOEXPERIMENT") == "regabi" {
+			// In order to make it easier to port runtime assembly
+			// to the register ABI, we introduce a macro
+			// indicating the experiment is enabled.
+			//
+			// Note: a similar change also appears in
+			// cmd/go/internal/work/gc.go.
+			//
+			// TODO(austin): Remove this once we commit to the
+			// register ABI (#40724).
+			asmArgs = append(asmArgs, "-D=GOEXPERIMENT_REGABI=1")
+		}
+	}
 
 	// Collect symabis from assembly code.
 	var symabis string
@@ -1733,3 +1748,23 @@ func cmdlist() {
 		fatalf("write failed: %v", err)
 	}
 }
+
+// IsRuntimePackagePath examines 'pkgpath' and returns TRUE if it
+// belongs to the collection of "runtime-related" packages, including
+// "runtime" itself, "reflect", "syscall", and the
+// "runtime/internal/*" packages. See also the function of the same
+// name in cmd/internal/objabi/path.go.
+func IsRuntimePackagePath(pkgpath string) bool {
+	rval := false
+	switch pkgpath {
+	case "runtime":
+		rval = true
+	case "reflect":
+		rval = true
+	case "syscall":
+		rval = true
+	default:
+		rval = strings.HasPrefix(pkgpath, "runtime/internal")
+	}
+	return rval
+}

src/cmd/go/internal/work/gc.go

@@ -292,15 +292,21 @@ func asmArgs(a *Action, p *load.Package) []interface{} {
 			}
 		}
 	}
-	if p.ImportPath == "runtime" && objabi.Regabi_enabled != 0 {
+	if objabi.IsRuntimePackagePath(pkgpath) {
+		args = append(args, "-compilingRuntime")
+		if objabi.Regabi_enabled != 0 {
 			// In order to make it easier to port runtime assembly
 			// to the register ABI, we introduce a macro
 			// indicating the experiment is enabled.
 			//
+			// Note: a similar change also appears in
+			// cmd/dist/build.go.
+			//
 			// TODO(austin): Remove this once we commit to the
 			// register ABI (#40724).
 			args = append(args, "-D=GOEXPERIMENT_REGABI=1")
 		}
+	}
 
 	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
 		// Define GOMIPS_value from cfg.GOMIPS.