Date: Wed, 21 Apr 2010 20:18:13 +0200 From: Roman Divacky <rdivacky@FreeBSD.org> To: Alexander Best <alexbestms@wwu.de> Cc: freebsd-current@FreeBSD.org Subject: Re: [CFT]: ClangBSD is selfhosting, we need testers now Message-ID: <20100421181813.GA97446@freebsd.org> In-Reply-To: <permail-201004211722001e86ffa800003aa3-a_best01@message-id.uni-muenster.de> References: <20100421152338.GA77210@freebsd.org> <permail-201004211722001e86ffa800003aa3-a_best01@message-id.uni-muenster.de>
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On Wed, Apr 21, 2010 at 07:22:00PM +0200, Alexander Best wrote:
> Roman Divacky schrieb am 2010-04-21:
> > On Wed, Apr 21, 2010 at 05:20:57PM +0200, Alexander Best wrote:
> > > i might have stumbled upon a problem with clang. i've compiled a
> > > kernel from
> > > the clang branch using `make kernel INSTKERNNAME=clang` and booted
> > > from it.
> > > i'm now experiencing audio problems with mp3s and certain video
> > > files.
> > > playback is awfully slow and the audio output gets distorted
> > > massively. `top`
> > > however reports no high cpu load and `vmstat -i` doesn't report
> > > anything
> > > unusual either.
>
> > > this problem doesn't occur with a regular gcc-kernel.
>
> > > both kernels are running under a regular (gcc) world.
>
> > > i thought it might be a problem with acpi, but disabling acpi
> > > (hint.acpi.0.disabled=1) gives me a system freeze.
>
> > I've heard about this problem but did not manage to reproduce that.
>
> > can you try to bisect what file is being miscompiled? ie. compile
> > half of the kernel with gcc and half with clang and bisect this
> > way to a single file.
>
> > we can work from there...
>
> i've identified the problem to be somewhere in sys/dev/sound. i've removed
> "device sound" and "device hda_snd" from my kernel config and
> rebuild/reinstalled both kernels (gcc and clang). i then booted the clang
> kernel and loaded various sound.ko and snd_hda.ko combination. here're the
> results:
>
> sound.ko (clang) snd_hda.ko (clang) => BROKEN
> sound.ko (clang) snd_hda.ko (gcc) => BROKEN
> sound.ko (gcc) snd_hda.ko (gcc) => OK
> sound.ko (gcc) snd_hda.ko (clang) => OK
great work! it looks like sound.ko is the culprit..
this is amd64 because my i386 kernel plays sound just fine.
could you try to bisect the sound.ko ?
you can do it this way:
1) cd modules/sound/sound && make CC=gcc
2) make -V SRCS | tr " " "\n" | grep -v \.h | sort | grep "^[a-m].*" | xargs touch
^^^^^ this is your bisect pattern
3) make CC=clang && make install
4) reload the module && test the sound
5) if the sound works you swap your bisect pattern (ie. [a-m] -> [n-z] etc.)
if not you know that you that the miscompiled file is in you pattern and
you can narrow it (ie. [a-m] -> [a-g] etc.)
6) goto 1 until you compile a single file
I am pretty sure you can understand this and reduce this to a single file.
once we get single file that is being miscompiled we can do some slightly
\more educated guess on whats going on and structure our testing a little
smarter...
thnx! roman
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