GCC 4.5

Over the last week, I’ve been updating my eeePC’s Gentoo linux to run GCC 4.5 and recompiling every package. The main reason is that now almost all my software is fully optimized for the Intel Atom processor. With only 1 relatively small hack, the rebuild went fairly smooth and my CFLAGS now contain “-march=atom -mtune=atom” !

The one small hack was placing a sed command inside the gcc 4.5 ebuild. It will build the first time without the command, but all subsequent builds will fail with an error that stage 2 and stage 3 are different. Here’s the line added to the src_unpack part of the ebuild: (Note: wrapping added)

[[ ${CFLAGS} == *-march=atom* ]] && sed -i 
    -e 's/(INSN_P/(NONDEBUG_INSN_P/g' 
    -e 's/!INSN_P/!NONDEBUG_INSN_P/g' 

To keep it safe, the line check if you $CFLAGS has -march=atom in it. If so, then it runs the following sed command. Originally issued as a patch for gcc for all of us running an Atom processor(s), I swapped it around to a sed command, as a few forum posts pointed out.

Beyond making the ‘overlay ebuild’, there was only 1 other snag, and that was binutils. Using the new gcc, binutils just wouldn’t compile. The error was about the movbe instruction. Upgrading from 2.18 to 2.19 using the old gcc compiler did the trick. After that it was just a matter of waiting for all the packages to recompile.

If anyone is thinking about upgrading to gcc 4.5 on gentoo, it’s not all that bad. Make sure to read the Gentoo GCC Upgrading Guide before you do anything. Also, run a “cat /proc/cpuinfo” to get the model of atom processor and make sure your CFLAGS are set properly.