cmd/dist: add GO_TEST_ASMFLAGS to set -asmflags during dist test

If we run into a need for finer control over when -asmflags gets set,
there can be an asmflags field added to goTest, analogously to the
existing gcflags and ldflags fields. Start with a minimal change for
what is currently needed, since not adding something we ourselves don't
use makes it easier to avoid inadvertently ending up maintaining it
because we can't be sure whether someone else started to depend on it.

For #77427.

Change-Id: I5e80874861cadf95fe770af6712b2c3f172c990a
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-spectre
Reviewed-on: https://go-review.googlesource.com/c/go/+/758740
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>

3 files changed, 20 insertions, 7 deletions

diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 78213a7a55..b09c3f2ce8 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -30,6 +30,8 @@ func cmdtest() {
 
 	var t tester
 
+	t.asmflags = os.Getenv("GO_TEST_ASMFLAGS")
+
 	var noRebuild bool
 	flag.BoolVar(&t.listMode, "list", false, "list available tests")
 	flag.BoolVar(&t.rebuild, "rebuild", false, "rebuild everything first")
@@ -63,6 +65,10 @@ type tester struct {
 	failed      bool
 	keepGoing   bool
 	compileOnly bool // just try to compile all tests, but no need to run
+	short       bool
+	cgoEnabled  bool
+	asmflags    string
+	json        bool
 	runRxStr    string
 	runRx       *regexp.Regexp
 	runRxWant   bool     // want runRx to match (true) or not match (false)
@@ -70,10 +76,6 @@ type tester struct {
 	banner      string   // prefix, or "" for none
 	lastHeading string   // last dir heading printed
 
-	short      bool
-	cgoEnabled bool
-	json       bool
-
 	tests        []distTest // use addTest to extend
 	testNames    map[string]bool
 	timeoutScale int
@@ -478,6 +480,9 @@ func (opts *goTest) buildArgs(t *tester) (build, run, pkgs, testFlags []string,
 	if opts.ldflags != "" {
 		build = append(build, "-ldflags="+opts.ldflags)
 	}
+	if t.asmflags != "" {
+		build = append(build, "-asmflags="+t.asmflags)
+	}
 	if opts.buildmode != "" {
 		build = append(build, "-buildmode="+opts.buildmode)
 	}
@@ -806,7 +811,7 @@ func (t *tester) registerTests() {
 	}
 
 	// Spectre mitigation smoke test.
-	if goos == "linux" && goarch == "amd64" {
+	if goos == "linux" && goarch == "amd64" && !(gogcflags == "-spectre=all" && t.asmflags == "all=-spectre=all") {
 		// Pick a bunch of packages known to have some assembly.
 		pkgs := []string{"internal/runtime/...", "reflect", "crypto/..."}
 		if !t.short {
diff --git a/src/internal/testenv/testenv_test.go b/src/internal/testenv/testenv_test.go
index 769db3a033..8313079983 100644
--- a/src/internal/testenv/testenv_test.go
+++ b/src/internal/testenv/testenv_test.go
@@ -97,8 +97,9 @@ func TestHasGoBuild(t *testing.T) {
 			}
 		}
 
-		if strings.Contains(b, "-noopt") {
-			// The -noopt builder sets GO_GCFLAGS, which causes tests of 'go build' to
+		if strings.Contains(b, "-noopt") ||
+			strings.Contains(b, "-spectre") {
+			// These builders set GO_GCFLAGS, which causes tests of 'go build' to
 			// be skipped.
 			t.Logf("HasGoBuild is false on %s", b)
 			return
diff --git a/src/run.bash b/src/run.bash
index cb474325c4..e774f03b30 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -21,6 +21,13 @@
 #
 # GO_TEST_TIMEOUT_SCALE: a non-negative integer factor to scale test timeout by.
 # Defaults to 1.
+#
+# GO_TEST_ASMFLAGS: Additional go tool asm arguments to use when running the tests.
+# This environment variable is an internal implementation detail between the
+# Go build system (x/build) and cmd/dist to enable builders that need to control this,
+# and will be removed if it stops being needed, or if a more general-purpose
+# GO_ASMFLAGS environment variable gets added to make.bash and supersedes this
+# test-only subset of it. See go.dev/issue/77427.
 
 set -e