linux-kernel - Re: x86-64: Maintain 16-byte stack alignment

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Date:   Tue, 10 Jan 2017 09:05:28 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 6:39 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> BTW this is with Debian gcc 4.7.2 which does not allow an 8-byte
> stack alignment as attempted by the Makefile:

I'm pretty sure we have random asm code that may not maintain a
16-byte stack alignment when it calls other code (including, in some
cases, calling C code).

So I'm not at all convinced that this is a good idea. We shouldn't
expect 16-byte alignment to be something trustworthy.

                 Linus