gcc-3.4.2 or libpthread bug?

[Peter Seiderer]

> Peter Seiderer wrote:
> > the following attached testprogramm gives a SIGSEGV when compiled
> > with gcc-3.4.2 and '-march=pentium4 -O2' on my Linux box (Suse-8.2),
> > I think because of a misaligned movapd.
> > Is it a gcc or a libpthread bug?
> 
> I think it could be argued that both are broken.
> 
> Gcc is broken because it is emitting SSE vector instructions even though 
> you didn't ask for them and the ABI doesn't support them.  The problem 
> is in the i386.md negdf2 pattern which emits a movapd if TARGET_SSE2 is 
> true, and -march=pentium4 turns on TARGET_SSE2.  The 32-bit x86 ABI says 
> that the stack has only 32-bit alignment, so it is not safe to use these 
> instructions behind the user's back.
> 
> I see two possible ways to fix this.  One is to change the code so that 
> TARGET_SSE2 is only enabled for 32-bit code if the user specifies 
> -msse2.  This would then be double checked against the CPU target to 
> make sure the CPU supports it.  There needs to be a distinction here 
> between whether the processor supports the feature, and whether the user 
> asked for it to be used.
> 
> The other possible solution is to modify the negdf2 pattern to check 
> TARGET_64BIT (or something equivalent), so that we only emit movapd when 
> we know that it is safe.  This is simpler, and probably better.
> 
> It can also be argued that libpthread is broken.  Although the ABI only 
> requires 32-bit alignment, new processor features such as SSE require 
> 64-bit alignment for some instructions, and hence if you want to be able 
> to use all processor features, you must align stacks to 64-bits even 
> though the ABI only requires 32-bits.
> 
> I'd suggest filing a bug report into bugzilla if you haven't already 
> done so, so we can track the problem.
> -- 
> Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com
> 

Thanks for your answer and the suggested fix.
There is already a bug report #14776 
    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14776
reported first againts 3.4.0, but no action taken since march 2004,
mayby because the bugreport is targeted for i686-pc-cygwin....

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