runtime: mark string comparison hooks as no split

These functions can be inserted by the compiler into the code to be
instrumented. This may result in these functions having callers that
are nosplit. That is why they must be nosplit.

Author: kyakdan

src/runtime/libfuzzer.go

@@ -92,6 +92,8 @@ func init() {
 //  4. result: an integer representing the comparison result. 0 indicates
 //     equality (comparison will ignored by libfuzzer), non-zero indicates a
 //     difference (comparison will be taken into consideration).
+//
+//go:nosplit
 func libfuzzerHookStrCmp(s1, s2 string, fakePC int) {
 	if s1 != s2 {
 		libfuzzerCall4(&__sanitizer_weak_hook_strcmp, uintptr(fakePC), cstring(s1), cstring(s2), uintptr(1))
@@ -102,6 +104,8 @@ func libfuzzerHookStrCmp(s1, s2 string, fakePC int) {
 
 // This function has now the same implementation as libfuzzerHookStrCmp because we lack better checks
 // for case-insensitive string equality in the runtime package.
+//
+//go:nosplit
 func libfuzzerHookEqualFold(s1, s2 string, fakePC int) {
 	if s1 != s2 {
 		libfuzzerCall4(&__sanitizer_weak_hook_strcmp, uintptr(fakePC), cstring(s1), cstring(s2), uintptr(1))