cmd/cgo/internal/testsanitizers: fix msan test failing with clang >= 16

Clang 16 introduced a more aggressive behavior regarding uninitialized
memory in the memory sanitizer.

The new option -fsanitize-memory-param-retval is enabled by default
and makes the test msan8 fail, since it uses an
uninitialized variable on purpose.

Disable this behavior if we are running with clang 16+.

Fixes #64616

Change-Id: If366f978bef984ea73f6ae958f24c8fce99b59fe
GitHub-Last-Rev: 60bd64a8fb
GitHub-Pull-Request: golang/go#64691
Reviewed-on: https://go-review.googlesource.com/c/go/+/549297
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/cgo/internal/testsanitizers/msan_test.go

@@ -71,7 +71,10 @@ func TestMSAN(t *testing.T) {
 			defer dir.RemoveAll(t)
 
 			outPath := dir.Join(name)
-			mustRun(t, config.goCmdWithExperiments("build", []string{"-o", outPath, srcPath(tc.src)}, tc.experiments))
+			buildcmd := config.goCmdWithExperiments("build", []string{"-o", outPath, srcPath(tc.src)}, tc.experiments)
+			// allow tests to define -f flags in CGO_CFLAGS
+			replaceEnv(buildcmd, "CGO_CFLAGS_ALLOW", "-f.*")
+			mustRun(t, buildcmd)
 
 			cmd := hangProneCmd(outPath)
 			if tc.wantErr {

src/cmd/cgo/internal/testsanitizers/testdata/msan8.go

@@ -5,6 +5,13 @@
 package main
 
 /*
+// For clang >= 16, uninitialized memory is more aggressively reported.
+// Restore the old behavior for this particular test as it relies on
+// uninitialized variables. See #64616
+#if __clang_major__ >= 16
+#cgo CFLAGS: -fno-sanitize-memory-param-retval
+#endif
+
 #include <pthread.h>
 #include <signal.h>
 #include <stdint.h>