fix incorrect reading of cpuinfo on POWER systems

This patch provides a rewrite of how /proc/cpuinfo is parsed in common_jag.c, as the original code made the incorrect assumption that cpuinfo follows a sane format across architectures ;-)

The motivation for this patch is that the original code was producing stack smashing on a POWER7 running RHEL6.4 Red Hat adds -fstack-protector along with a lot of other protective CFLAGS when building RPMs. The code ran okay with -fno-stack-protector, but that is not the best work-around.

So, the relevant /proc/cpuinfo line on an Intel (Xeon X5675) system looks like:

cpu MHz                : 3066.915

Whereas the relevant line in a POWER7 system is

clock                : 3550.000000MHz

My patch replaces the assumption that the relevant number starts 11 characters into the string with another assumption: That the relevant number starts two characters after a colon in a string that matches (M|G)Hz.

All in all, the function has a few more calls, which may be a performance issue if it has to be called multiple times, but since the section I edited only gets evaluated if we don't know the cpu frequency, getting it right will actually result in fewer string operations and unnecessary opens of /proc/cpuinfo for systems likewise affected.

Finally, I also read the actual value into a double and multiply it up to the size indicated by the suffix, so we end up with KHz? It was unclear what the original code intended, since it matched both MHz and GHz, replaced the decimal point with a zero, and read the result as an int.

--
Chandler Wilkerson
Center for Research Computing
Rice University