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

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Message-ID: <CA+=Sn1njFZ-XZRHJdmjzOyvXvcMXg+oBao=wK8w3RXN_Ji=fLA@mail.gmail.com>
Date:   Mon, 22 Feb 2021 01:29:23 -0800
From:   Andrew Pinski <pinskia@...il.com>
To:     "Michael J. Baars" <mjbaars1977.gcc@...erfiber.eu>
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, 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.

Thanks,
Andrew

>
> Regards,
> Mischa.