gcc 4.7: -march=corei7-avx bug?

gcc 4.7: -march=corei7-avx bug?

[Dâniel Fraga]

	I tried to compile Firefox 11 with gcc 4.7 optimized with:

-O3 -march=corei7-avx (I have a core i7 2700k)

	But Firefox segfaults (backtrace provided, although it seems
not very useful):

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52762

	If I compile with -march=corei7 it runs perfectly.

	Maybe a gcc bug?

	How can I help you to debug this?

	Thanks!

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Re: gcc 4.7: -march=corei7-avx bug?

[Jakub Jelinek]

On Thu, Mar 29, 2012 at 04:53:45AM -0300, Dâniel Fraga wrote:
> 	I tried to compile Firefox 11 with gcc 4.7 optimized with:
> 
> -O3 -march=corei7-avx (I have a core i7 2700k)
> 
> 	But Firefox segfaults (backtrace provided, although it seems
> not very useful):
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52762
> 
> 	If I compile with -march=corei7 it runs perfectly.
> 
> 	Maybe a gcc bug?

Maybe.  Or maybe firefox bug.

> 	How can I help you to debug this?

Build with debug info, try to understand why it crashed, build
a minimal testcase out of it, attach it to the PR.
Or you could use a brute force method, if -march=corei7 works,
but -march=corei7-avx doesn't, do a binary search on firefox built with
some corei7 and some corei7-avx object files, until you find the problematic
compilation unit.

	Jakub

Re: gcc 4.7: -march=corei7-avx bug?

[Dâniel Fraga]

On Thu, 29 Mar 2012 10:26:47 +0200
Jakub Jelinek <jakub@redhat.com> wrote:

> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52762

> Build with debug info, try to understand why it crashed, build
> a minimal testcase out of it, attach it to the PR.
> Or you could use a brute force method, if -march=corei7 works,
> but -march=corei7-avx doesn't, do a binary search on firefox built with
> some corei7 and some corei7-avx object files, until you find the problematic
> compilation unit.

	Hi Jakub, I posted a new backtrace with --enable-debug to
the above bug report. I hope it helps.

	If you need more testing or want em to apply some patch, just
ask. Thanks.

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Re: gcc 4.7: -march=corei7-avx bug?

[Ryan Hill]

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On Thu, 29 Mar 2012 04:53:45 -0300
Dâniel Fraga <fragabr@gmail.com> wrote:

> 	I tried to compile Firefox 11 with gcc 4.7 optimized with:
> 
> -O3 -march=corei7-avx (I have a core i7 2700k)
> 
> 	But Firefox segfaults (backtrace provided, although it seems
> not very useful):
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52762
> 
> 	If I compile with -march=corei7 it runs perfectly.
> 
> 	Maybe a gcc bug?
> 
> 	How can I help you to debug this?

We've had to disable -mavx for firefox builds due to numerous issues like
this.  Search the mozilla bugzilla for stack alignment issues.


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