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CCache and multiple Gcc versions

I'm using the ccache utility in my OpenOffice.org builds to speed up builds. Basically, ccache stores the results of the builds in a cache directory. When you build with ccache gcc ..., it first generate a solid MD4 hash and checks in its cache if the build result is already available so it can be returned directly instead of being compiled.

ccache is very useful in large applications like OpenOffice.org because you can hardly get a change to every source file, and a lot of the build results are already computed before you start a fresh build for next version. As an example, the ccache directory on the PowerMac G5 is more that 1GB big, and is only filled with OO.org object files.

But I was wondering if ccache was able to make the difference between Gcc 3.3 and Gcc 4.0. Indeed, I think the 3.x branch has a different compilation behavior than the 4.x branch. You can check it quickly by compiling the same source file with Gcc 3.3 and Gcc 4.0 : the md5 will differ for the resulting executable file.

So how does this really work ? Is it safe to use the same ccache directory between a complete Gcc 3.3 build and the Gcc 4.0 build ? I would tend not to say so, but I would like an expert point of vue on it ;) Any idea or comment ?

OpenOffice.org Tinderbox

A few months ago, Eric Bachard, co-leader of the OpenOffice.org's Porting project, told me he would like to see a Tinderbox build slave for the Mac OS X version of OO.org by the end of the year. About two or three weeks later, a brand new PowerMac G5 was proudly standing in the middle of my apartment. I never used a Mac nor built OO.org before (I don't really use it too, by the way), and I had to turn this 40 pounds of aluminum and electronics into an fully automated builder of the OpenOffice.org source tree ...