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

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Message-ID: <20170113083927.GC22022@gondor.apana.org.au>
Date:   Fri, 13 Jan 2017 16:39:27 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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 05:46:55PM -0800, Andy Lutomirski wrote:
> 
> What I mean is: what guarantees that the stack is properly aligned for
> the subroutine call?  gcc promises to set up a stack frame, but does
> it promise that rsp will be properly aligned to call a C function?

Yes, as long as you don't go behind its back and start directly
pushing things onto the stack with inline asm.

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