internal/cpu: move GODEBUGCPU options into GODEBUG

Change internal/cpu feature configuration to use
GODEBUG=cpu.feature1=value,cpu.feature2=value...
instead of GODEBUGCPU=feature1=value,feature2=value... .

This is not a backwards compatibility breaking change
since GODEBUGCPU was introduced in go1.11 as an
undocumented compiler experiment.

Fixes #28757

Change-Id: Ib21b3fed2334baeeb061a722ab1eb513d1137e87
Reviewed-on: https://go-review.googlesource.com/c/149578
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/internal/cpu/cpu.go

@@ -6,7 +6,8 @@
 // used by the Go standard library.
 package cpu
 
-// DebugOptions is set to true by the runtime if the OS supports GODEBUGCPU.
+// DebugOptions is set to true by the runtime if the OS supports reading
+// GODEBUG early in runtime startup.
 // This should not be changed after it is initialized.
 var DebugOptions bool
 
@@ -130,13 +131,14 @@ type s390x struct {
 
 // Initialize examines the processor and sets the relevant variables above.
 // This is called by the runtime package early in program initialization,
-// before normal init functions are run. env is set by runtime if the OS supports GODEBUGCPU.
+// before normal init functions are run. env is set by runtime if the OS supports
+// cpu feature options in GODEBUG.
 func Initialize(env string) {
 	doinit()
 	processOptions(env)
 }
 
-// options contains the cpu debug options that can be used in GODEBUGCPU.
+// options contains the cpu debug options that can be used in GODEBUG.
 // Options are arch dependent and are added by the arch specific doinit functions.
 // Features that are mandatory for the specific GOARCH should not be added to options
 // (e.g. SSE2 on amd64).
@@ -146,16 +148,16 @@ var options []option
 type option struct {
 	Name      string
 	Feature   *bool
-	Specified bool // whether feature value was specified in GODEBUGCPU
+	Specified bool // whether feature value was specified in GODEBUG
 	Enable    bool // whether feature should be enabled
 	Required  bool // whether feature is mandatory and can not be disabled
 }
 
 // processOptions enables or disables CPU feature values based on the parsed env string.
-// The env string is expected to be of the form feature1=value1,feature2=value2...
+// The env string is expected to be of the form cpu.feature1=value1,cpu.feature2=value2...
 // where feature names is one of the architecture specifc list stored in the
 // cpu packages options variable and values are either 'on' or 'off'.
-// If env contains all=off then all cpu features referenced through the options
+// If env contains cpu.all=off then all cpu features referenced through the options
 // variable are disabled. Other feature names and values result in warning messages.
 func processOptions(env string) {
 field:
@@ -167,12 +169,15 @@ field:
 		} else {
 			field, env = env[:i], env[i+1:]
 		}
+		if len(field) < 4 || field[:4] != "cpu." {
+			continue
+		}
 		i = indexByte(field, '=')
 		if i < 0 {
-			print("GODEBUGCPU: no value specified for \"", field, "\"\n")
+			print("GODEBUG: no value specified for \"", field, "\"\n")
 			continue
 		}
-		key, value := field[:i], field[i+1:]
+		key, value := field[4:i], field[i+1:] // e.g. "SSE2", "on"
 
 		var enable bool
 		switch value {
@@ -181,7 +186,7 @@ field:
 		case "off":
 			enable = false
 		default:
-			print("GODEBUGCPU: value \"", value, "\" not supported for option ", key, "\n")
+			print("GODEBUG: value \"", value, "\" not supported for cpu option \"", key, "\"\n")
 			continue field
 		}
 
@@ -201,7 +206,7 @@ field:
 			}
 		}
 
-		print("GODEBUGCPU: unknown cpu feature \"", key, "\"\n")
+		print("GODEBUG: unknown cpu feature \"", key, "\"\n")
 	}
 
 	for _, o := range options {
@@ -210,12 +215,12 @@ field:
 		}
 
 		if o.Enable && !*o.Feature {
-			print("GODEBUGCPU: can not enable \"", o.Name, "\", missing hardware support\n")
+			print("GODEBUG: can not enable \"", o.Name, "\", missing CPU support\n")
 			continue
 		}
 
 		if !o.Enable && o.Required {
-			print("GODEBUGCPU: can not disable \"", o.Name, "\", required feature\n")
+			print("GODEBUG: can not disable \"", o.Name, "\", required CPU feature\n")
 			continue
 		}
 

src/internal/cpu/cpu_test.go

@@ -41,7 +41,7 @@ func runDebugOptionsTest(t *testing.T, test string, options string) {
 
 	testenv.MustHaveExec(t)
 
-	env := "GODEBUGCPU=" + options
+	env := "GODEBUG=" + options
 
 	cmd := exec.Command(os.Args[0], "-test.run="+test)
 	cmd.Env = append(cmd.Env, env)
@@ -58,14 +58,14 @@ func runDebugOptionsTest(t *testing.T, test string, options string) {
 }
 
 func TestDisableAllCapabilities(t *testing.T) {
-	runDebugOptionsTest(t, "TestAllCapabilitiesDisabled", "all=off")
+	runDebugOptionsTest(t, "TestAllCapabilitiesDisabled", "cpu.all=off")
 }
 
 func TestAllCapabilitiesDisabled(t *testing.T) {
 	MustHaveDebugOptionsSupport(t)
 
-	if os.Getenv("GODEBUGCPU") != "all=off" {
-		t.Skipf("skipping test: GODEBUGCPU=all=off not set")
+	if os.Getenv("GODEBUG") != "cpu.all=off" {
+		t.Skipf("skipping test: GODEBUG=cpu.all=off not set")
 	}
 
 	for _, o := range Options {

src/internal/cpu/cpu_x86_test.go

@@ -20,14 +20,14 @@ func TestX86ifAVX2hasAVX(t *testing.T) {
 }
 
 func TestDisableSSE2(t *testing.T) {
-	runDebugOptionsTest(t, "TestSSE2DebugOption", "sse2=off")
+	runDebugOptionsTest(t, "TestSSE2DebugOption", "cpu.sse2=off")
 }
 
 func TestSSE2DebugOption(t *testing.T) {
 	MustHaveDebugOptionsSupport(t)
 
-	if os.Getenv("GODEBUGCPU") != "sse2=off" {
-		t.Skipf("skipping test: GODEBUGCPU=sse2=off not set")
+	if os.Getenv("GODEBUG") != "cpu.sse2=off" {
+		t.Skipf("skipping test: GODEBUG=cpu.sse2=off not set")
 	}
 
 	want := runtime.GOARCH != "386" // SSE2 can only be disabled on 386.
@@ -37,14 +37,14 @@ func TestSSE2DebugOption(t *testing.T) {
 }
 
 func TestDisableSSE3(t *testing.T) {
-	runDebugOptionsTest(t, "TestSSE3DebugOption", "sse3=off")
+	runDebugOptionsTest(t, "TestSSE3DebugOption", "cpu.sse3=off")
 }
 
 func TestSSE3DebugOption(t *testing.T) {
 	MustHaveDebugOptionsSupport(t)
 
-	if os.Getenv("GODEBUGCPU") != "sse3=off" {
-		t.Skipf("skipping test: GODEBUGCPU=sse3=off not set")
+	if os.Getenv("GODEBUG") != "cpu.sse3=off" {
+		t.Skipf("skipping test: GODEBUG=cpu.sse3=off not set")
 	}
 
 	want := false

src/runtime/proc.go

@@ -476,10 +476,10 @@ const (
 	_GoidCacheBatch = 16
 )
 
-// cpuinit extracts the environment variable GODEBUGCPU from the environment on
-// Linux and Darwin and calls internal/cpu.Initialize.
+// cpuinit extracts the environment variable GODEBUG from the environment on
+// Unix-like operating systems and calls internal/cpu.Initialize.
 func cpuinit() {
-	const prefix = "GODEBUGCPU="
+	const prefix = "GODEBUG="
 	var env string
 
 	switch GOOS {
@@ -487,7 +487,7 @@ func cpuinit() {
 		cpu.DebugOptions = true
 
 		// Similar to goenv_unix but extracts the environment value for
-		// GODEBUGCPU directly.
+		// GODEBUG directly.
 		// TODO(moehrmann): remove when general goenvs() can be called before cpuinit()
 		n := int32(0)
 		for argv_index(argv, argc+1+n) != nil {