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

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Message-ID: <20170111031124.GA4515@gondor.apana.org.au>
Date:   Wed, 11 Jan 2017 11:11:24 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 09:05:28AM -0800, Linus Torvalds wrote:
> 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.

Well the only other alternative I see is to ban compilers which
enforce 16-byte stack alignment, such as gcc 4.7.2.  Or is there
another way?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt