[Buildroot] still trusting ccache ?

Sagaert Johan sagaert.johan at skynet.be
Wed Nov 27 09:43:59 UTC 2013

 Hi Arnout,

Could be GCC version related,
I have some projects that use other GCC versions and I did'nt clean the cache the last year I think.

Another problem is that is that :
make distclean

make someconfig_defconfig  ( <-------- one with ccache enabled )
make uclibc-menuconfig     ( <-- not working )

Regards, Johan

-----Oorspronkelijk bericht-----
Van: Arnout Vandecappelle [mailto:arnout at mind.be] 
Verzonden: dinsdag 26 november 2013 23:11
Aan: Sagaert Johan
CC: buildroot at busybox.net
Onderwerp: Re: [Buildroot] still trusting ccache ?

On 25/11/13 22:13, Sagaert Johan wrote:
> Hi all;
> Last weekend I had an strange build error building libglib when ccache was enabled:
> (something thread related)
> - A clean build with ccache on  -> Failed
> - A clean build with ccache off -> Ok
> - Deleted the whole buildroot-ccache directory tree
> - A clean build with ccache on -> Ok !!

  Is it possible that you changed compiler? We have disabled hashing the compiler in ccache about a year ago, but the result of that
is that the cached results are wrong when you switch to a different compiler.

  One big problem is that in the current situation, changing the compiler isn't even detected if you switch output directory.
Fortunately, ccache still hashes the basename of the compiler, so when you switch architectures, ccache will not use the wrong
object files.

  There has been a discussion about this a couple of weeks ago [1] so the situation will hopefully change again in the near future.

[1] http://lists.busybox.net/pipermail/buildroot/2013-November/083028.html

> In my build I only gain 3 minutes (10%) in time.

  If you don't gain anything, there's certainly no point to use ccache of course. Other people have reported much larger gains.

> I have some doubts on trusting ccache after this experience.
> So I think that some un-reproducable build errors could be ccache related as well.

  I don't think that any of the autobuilders use ccache. Though perhaps 
they should, so we would detect these problems. But at the moment it 
wouldn't be a good idea because we know it would fail :-)

> PS I noticed that besides .buildroot-ccache there is also a .ccache created when building.

  Hm, that's strange...


> Regards
> Sagaert Johan
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Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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