linux-kernel - Re: problems with memory allocation and the alignment check

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Message-ID: <d9a2cdcf116ed32874ed02bd6fa60ad899ce5f50.camel@cyberfiber.eu>
Date:   Mon, 22 Feb 2021 10:37:33 +0100
From:   "Michael J. Baars" <mjbaars1977.gcc@...erfiber.eu>
To:     Andrew Pinski <pinskia@...il.com>
Cc:     GCC Mailing List <gcc@....gnu.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: problems with memory allocation and the alignment check

On Mon, 2021-02-22 at 01:29 -0800, Andrew Pinski wrote:
> On Mon, Feb 22, 2021 at 1:17 AM Michael J. Baars
> <mjbaars1977.gcc@...erfiber.eu> wrote:
> > Hi,
> > 
> > I just wrote this little program to demonstrate a possible flaw in both malloc and calloc.
> > 
> > If I allocate a the simplest memory region from main(), one out of three optimization flags fail.
> > If I allocate the same region from a function, three out of three optimization flags fail.
> > 
> > Does someone know if this really is a flaw, and if so, is it a gcc or a kernel flaw?
> 
> There is no flaw.  GCC (kernel, glibc) all assume unaligned accesses
> on x86 will not cause an exception.

Is this just an assumption or more like a fact? I agree with you that byte aligned is more or less the same as unaligned.

> 
> Thanks,
> Andrew
> 
> > Regards,
> > Mischa.