[aarch64-port-dev ] hotspot jtreg runtime/BoolReturn/JNIBooleanTest.java failure

[Andrew Haley]

Here's the bug in Java's runtime which provoked this error:

JNIEXPORT jboolean JNICALL
Java_java_io_Console_echo(JNIEnv *env,
                          jclass cls,
                          jboolean on)
{
    struct termios tio;
    jboolean old;
    int tty = fileno(stdin);
    if (tcgetattr(tty, &tio) == -1) {
        JNU_ThrowIOExceptionWithLastError(env, "tcgetattr failed");
        return !on;
    }
    old = (tio.c_lflag & ECHO);
    if (on) {
        tio.c_lflag |= ECHO;
    } else {
        tio.c_lflag &= ~ECHO;
    }
    if (tcsetattr(tty, TCSANOW, &tio) == -1) {
        JNU_ThrowIOExceptionWithLastError(env, "tcsetattr failed");
    }
    return old;
}

It's super-hard to see the bug because you could (and I did) naively
assume that jboolean behaves like boolean (or C++ bool) but it
doesn't. It should be:

    old = (tio.c_lflag & ECHO) != 0;

which is why, I guess, the author wrapped the expression in
parentheses.

But note that if we simply fix this in HotSpot, it's only right by
accident: ECHO just happens to be 0000010, so we know the result of
(tio.c_lflag & ECHO) will fit in a jboolean, but that's just an
accident.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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