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Re: GCC 5 snapshots produce broken kernel for powerpc-e500v2-linux-gnuspe?



> On Sep 9, 2014, at 2:57 AM, Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> 
>> On 2014.09.09 at 17:35 +0800, Arseny Solokha wrote:
>> Hello,
>> 
>> I've recently faced an issue I'm afraid I currently unable to debug. When
>> building an arbitrary version of Linux kernel for powerpc-e500v2-linux-gnuspe
>> target, it seems gcc prior to 5 produces a good image which boots just fine, and
>> current gcc 5 snapshots (4.10.0-alpha20140810 for example) produce an image
>> which hangs just after U-Boot hands over to the kernel.
>> 
>> This behavior is well reproducible on real hardware as well as under qemu. I've
>> prepared a minimal kernel config which is dysfunctional as is but still enough
>> to demonstrate the problem in qemu. I believe the exact Linux version number
>> doesn't actually matter here, but see the attachment for details.
>> 
>> Compare the output produced by u-boot and this minified kernel build using
>> gcc 4.9.1 and 4.10.0-alpha20140810 snapshot.
>> 
>> I now have completely no idea what to do next to find a cause of (1) gcc 5
>> snapshots producing unbootable kernel, 
> 
> gcc trunk also miscompiles x86_64 kernels currently, but I haven't
> looked deeper yet. 
> The best way to narrow down the issue is to use git (or svn) bisect to
> find out which gcc revision causes the miscompile.  Then you can md5sum
> the kernel object files for the bad revision and for the first good
> revision and compare the results. After that you can look at the
> disassembly of the object files, for which md5sum differs, and try to
> figure out the reason why.


I have a patch which I need to submit. Maybe by Friday I will do that. It fixes the kernel on arm64 but it is generic c front-end patch. 

> 
> -- 
> Markus


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