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

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Message-ID: <20170113083648.GA22022@gondor.apana.org.au>
Date:   Fri, 13 Jan 2017 16:36:48 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote:
>
> I think we have some inline functions that do asm volatile ("call
> ..."), and I don't see any credible way of forcing alignment short of
> generating an entirely new stack frame and aligning that.  Ick.  This

A straight asm call from C should always work because gcc keeps
the stack aligned in the prologue.

The only problem with inline assembly is when you start pushing
things onto the stack directly.

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