When building the JDK native libs with opt-level HIGHEST on Alpine with gcc 12.2.1 (gcc (Alpine 12.2.1_git20220924-r10) 12.2.1 20220924) I run into this warning as error :

src/jdk.jdwp.agent/share/native/libjdwp/util.c:758:31: error: dangling pointer 'xx' to 'signature' may be used [-Werror=dangling-pointer=]
  758 | if (xx == NULL || *(xx + 1) == 0) {
                            | ^~~~~~~~~
 
src/jdk.jdwp.agent/share/native/libjdwp/util.c:715:11: note: 'signature' declared here
  715 | char *signature = NULL;
      | ^~~~~~~~~
cc1: all warnings being treated as errors

Disabling the dangling pointer warning for this file works as a workaround.

jvmtiError
methodReturnType(jmethodID method, char *typeKey)
{
    char *signature;
    jvmtiError error;

    signature = NULL;
    error = methodSignature(method, NULL, &signature, NULL);
    if (error == JVMTI_ERROR_NONE) {
        if (signature == NULL ) {
            error = AGENT_ERROR_INVALID_TAG;
        } else {
            char * xx;

            xx = strchr(signature, ')');
            if (xx == NULL || *(xx + 1) == 0) {
                error = AGENT_ERROR_INVALID_TAG;
            } else {
               *typeKey = *(xx + 1);
            }
            jvmtiDeallocate(signature);
        }
    }
    return error;
}