From: Andy Lutomirski <luto@amacapital.net>
Subject: Re: x86-64: Maintain 16-byte stack alignment
Date: Wed, 11 Jan 2017 10:20:45 -0800
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Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
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On Wed, Jan 11, 2017 at 12:09 AM, Herbert Xu
<herbert@gondor.apana.org.au> wrote:
> On Wed, Jan 11, 2017 at 08:06:54AM +0000, Ard Biesheuvel wrote:
>>
>> Couldn't we update the __aligned(x) macro to emit 32 if arch == x86
>> and x == 16? All other cases should work just fine afaict
>
> Not everyone uses that macro.  You'd also need to add some checks
> to stop people from using the gcc __attribute__ directly.
>

You'd also have to audit things to make sure that __aligned__(16)
isn't being used for non-stack purposes.  After all, __aligned__(16)
in static data is fine, and it's also fine as a promise to GCC that
some object is 16-byte aligned.

--Andy