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Date: Mon, 08 Mar 2010 15:46:00 -0000
Message-ID: <84fc9c001003080746p775b14b4s105ed0ddbf4a2fb1@mail.gmail.com>
Subject: Re: (un)aligned accesses on x86 platform.
From: Richard Guenther <richard.guenther@gmail.com>
To: =?ISO-8859-2?Q?Pawe=B3_Sikora?= <pluto@agmk.net>
Cc: gcc@gcc.gnu.org
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2010/3/8 Pawe=C5=82 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 rule=
s.
>
> so, is it possible to instruct gcc-x86 to always use suitable loads/stores
> like on sparc/arm?

Only by re-building it and setting STRICT_ALIGNMENT.

Richard.

> [1] "AC" bit - http://en.wikipedia.org/wiki/FLAGS_register_(computing)
>
> BR,
> Pawel.
>