linux-kernel - Re: gcc-4.3 considers unaligned accesses on X86 as undefined

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Message-ID: <87d4pinjbq.fsf@basil.nowhere.org>
Date:	26 Mar 2008 06:30:17 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Török Edwin <edwintorok@...il.com>
Cc:	"Thomas Gleixner mingo@...hat.com" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: gcc-4.3 considers unaligned accesses on X86 as undefined

Török Edwin <edwintorok@...il.com> writes:

> At -O3 it generates vectorized code that  _relies_  on the fact that
> pointers are always aligned (unless you use packed attributes, etc.),
> and the resulting code crashes if the pointer is unaligned.  (-O3 -msse
> on 32-bit, and simply -O3 on 64-bit since -msse is default)

The 2.6 kernel disables SSE and MMX code generation explicitely.
2.4 should be also safe unless someone misguided recompiles it with -O3.

-Andi
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