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Re: (un)aligned accesses on x86 platform.
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Paweł Sikora <pluto at agmk dot net>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 16 Mar 2010 06:50:30 -0800
- Subject: Re: (un)aligned accesses on x86 platform.
- References: <op.u889o5kpzu3k57@pawels.alatek.krakow.pl>
2010/3/8 PaweÅ Sikora <pluto@agmk.net>:
> hi,
>
> during development a cross platform appliacation on x86 workstation
> i've enabled an alignemnt checking [1] to catch possible erroneous
> code before it appears on client's sparc/arm cpu with sigbus ;)
>
> it works pretty fine and catches alignment violations but Jakub Jelinek
> had told me (on glibc bugzilla) that gcc on x86 can still dereference
> an unaligned pointer (except for vector insns).
> i suppose it means that gcc can emit e.g. movl for access a short int
> (or maybe others scenarios) in some cases and violates cpu alignment rules.
>
> so, is it possible to instruct gcc-x86 to always use suitable loads/stores
> like on sparc/arm?
>
> [1] "AC" bit - http://en.wikipedia.org/wiki/FLAGS_register_(computing)
>
I am interested in an -mstrict-alignment option for x86.
--
H.J.