internal/cpu: use 'off' for disabling cpu capabilities instead of '0'

Updates #27218

Change-Id: I4ce20376fd601b5f958d79014af7eaf89e9de613
Reviewed-on: https://go-review.googlesource.com/c/141818
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/internal/cpu/cpu.go

@@ -157,11 +157,11 @@ type option struct {
 }
 
 // processOptions disables CPU feature values based on the parsed env string.
-// The env string is expected to be of the form feature1=0,feature2=0...
+// The env string is expected to be of the form feature1=off,feature2=off...
 // where feature names is one of the architecture specifc list stored in the
-// cpu packages options variable. If env contains all=0 then all capabilities
+// cpu packages options variable. If env contains all=off then all capabilities
 // referenced through the options variable are disabled. Other feature
-// names and values other than 0 are silently ignored.
+// names and values other than 'off' are silently ignored.
 func processOptions(env string) {
 field:
 	for env != "" {
@@ -178,8 +178,8 @@ field:
 		}
 		key, value := field[:i], field[i+1:]
 
-		// Only allow turning off CPU features by specifying '0'.
-		if value == "0" {
+		// Only allow turning off CPU features by specifying 'off'.
+		if value == "off" {
 			if key == "all" {
 				for _, v := range options {
 					*v.Feature = false

src/internal/cpu/cpu_test.go

@@ -38,14 +38,14 @@ func runDebugOptionsTest(t *testing.T, test string, options string) {
 }
 
 func TestDisableAllCapabilities(t *testing.T) {
-	runDebugOptionsTest(t, "TestAllCapabilitiesDisabled", "all=0")
+	runDebugOptionsTest(t, "TestAllCapabilitiesDisabled", "all=off")
 }
 
 func TestAllCapabilitiesDisabled(t *testing.T) {
 	MustHaveDebugOptionsSupport(t)
 
-	if os.Getenv("GODEBUGCPU") != "all=0" {
-		t.Skipf("skipping test: GODEBUGCPU=all=0 not set")
+	if os.Getenv("GODEBUGCPU") != "all=off" {
+		t.Skipf("skipping test: GODEBUGCPU=all=off not set")
 	}
 
 	for _, o := range Options {

src/internal/cpu/cpu_x86_test.go

@@ -30,14 +30,14 @@ func TestX86ifAVX2hasAVX(t *testing.T) {
 }
 
 func TestDisableSSE2(t *testing.T) {
-	runDebugOptionsTest(t, "TestSSE2DebugOption", "sse2=0")
+	runDebugOptionsTest(t, "TestSSE2DebugOption", "sse2=off")
 }
 
 func TestSSE2DebugOption(t *testing.T) {
 	MustHaveDebugOptionsSupport(t)
 
-	if os.Getenv("GODEBUGCPU") != "sse2=0" {
-		t.Skipf("skipping test: GODEBUGCPU=sse2=0 not set")
+	if os.Getenv("GODEBUGCPU") != "sse2=off" {
+		t.Skipf("skipping test: GODEBUGCPU=sse2=off not set")
 	}
 
 	want := runtime.GOARCH != "386" // SSE2 can only be disabled on 386.