mktime bug back with gcc 4.3.2

[stecklum]

Binary package hint: autoconf

running configure on the archfs-0.5.4 tree showed that autoconf hangs for quite a while when checking for mktime. The result is

checking for working mktime... no

This happens on a 64bit fully updated 8.10 system, i.e. with the autoconf 2.61-7ubuntu1 package and gcc (Ubuntu 4.3.2-1ubuntu12). Updating autoconf with the Debian 2.63-2 package does not solve the problem.

[Matthias Klose (doko)]

please attach the source and header files used by the autoconf test

[Andrew Ferguson (adferguson)]

I can confirm this on 32bit fully updated 8.10 as well.

After some more testing, I can confirm this is a gcc bug because it is the -O2 flag which causes the problem. Without that, it is fine.

I have attached the source code to the test to this bug report. Compile like so:

$ gcc -o bar1 -O2 bar.c
$ gcc -o bar2 bar.c
$ ./bar1 [hangs]
$ ./bar2 [no hang]

(-O1 also has no problems)

[Andrew Ferguson (adferguson)]

Really, all that's needed is this part, which basically occurs on line 222 of the above bar.c:

void main() {
        int i = 0;

        for (i = 1; 0 < i; i *= 2) {
                if (0)
                        return;
        }

        return;
}

As you can see, the loop is designed to end when i wraps around and goes negative. With -O2, this doesn't happen for some reason.

[Andrew Ferguson (adferguson)]

For the record, re-running autoconf on the given project's files (archfs), updated the configure script so that it no longer writes the test in this way. The test then passes appropriately with Ubuntu 8.10.

I'll file a bug against the archfs project to update their configure script.

[Matthias Klose (doko)]

bug in the testcase. see gcc(1) -fwrapv how to work around this.