[Bug libc/12113] Segmentation fault in dynamic loader on AVX enabled OS and CPU with AVX

["hjl.tools at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=12113

--- Comment #16 from H.J. Lu <hjl.tools at gmail dot com> 2010-10-13 23:26:30 UTC ---
(In reply to comment #13)
> (In reply to comment #9)
> > Offset is good for up to 128byte alignment:
> > 
> > tcb-offsets.h:#define RTLD_SAVESPACE_SSE 128
> > 
> > But tcbhead_t is only aligned at 16byte. No matter
> > how much padding you add, rtld_savespace_sse can only
> > be guaranteed to be aligned at alignment of tcbhead_t.
> 
> I don't doubt that the patch does the job.
> 
> I don't like aligning the struct member.  The struct itself (tcbhead_t) should
> get the alignment element.  Otherwise we might silently introduce holes in the
> structure which are glossed over by the alignment of the struct element.
>

I posted an updated patch to increase TCB_ALIGNMENT to 32.

> 
> > This test happens to make tcbhead_t only aligned at
> > 16byte, not 32byte. My patch aligns tcbhead_t at maximum
> > register size so that rtld_savespace_sse is properly aligned.
> 
> And what is it about this test that does it?  There seems to be nothing
> special.  Any alignment introduced by this is incidental, based on the current
> implementation having specific sizes.

That is true. This test happens to align TCB at 16byte by chance.

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