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

From	Herbert Xu <herbert@gondor.apana.org.au>
Newsgroups	linux.kernel
Subject	Re: x86-64: Maintain 16-byte stack alignment
Date	2017-01-11 04:20 +0100
Message-ID	<sYhCa-1wa-11@gated-at.bofh.it> (permalink)
References	<sY5KF-2vR-21@gated-at.bofh.it> <sY8yR-4e0-15@gated-at.bofh.it> <sYa7E-5fe-37@gated-at.bofh.it>
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On Tue, Jan 10, 2017 at 11:00:31AM -0800, Andy Lutomirski wrote:
> 
> Here's what I think is really going on.  This is partially from
> memory, so I could be off base.  The kernel is up against
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383, which means that,
> on some GCC versions (like the bad one and maybe even current ones),
> things compiled without -mno-sse can't have the stack alignment set
> properly.  IMO we should fix this in the affected code, not the entry

No that's not it.  My compiler (gcc 4.7.2) doesn't support it period:

$ gcc -S -O2 -mno-sse -mpreferred-stack-boundary=3 a.c
a.c:1:0: error: -mpreferred-stack-boundary=3 is not between 4 and 12
$ 

So you either have to ban all compilers older than whatever version
that started supporting 8-byte stack alignment, or fix the kernel.

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

Thread

x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-10 15:40 +0100
  Re: x86-64: Maintain 16-byte stack alignment Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-10 18:40 +0100
    Re: x86-64: Maintain 16-byte stack alignment Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-10 20:20 +0100
      Re: x86-64: Maintain 16-byte stack alignment Andy Lutomirski <luto@amacapital.net> - 2017-01-10 20:30 +0100
        Re: x86-64: Maintain 16-byte stack alignment Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-10 21:10 +0100
          Re: x86-64: Maintain 16-byte stack alignment Andy Lutomirski <luto@amacapital.net> - 2017-01-11 00:30 +0100
            Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-11 04:30 +0100
        Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-11 04:30 +0100
    Re: x86-64: Maintain 16-byte stack alignment Andy Lutomirski <luto@amacapital.net> - 2017-01-10 20:50 +0100
      Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-11 04:20 +0100
    Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-11 04:20 +0100
    Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-12 07:20 +0100
      Re: x86-64: Maintain 16-byte stack alignment Herbert Xu <herbert@gondor.apana.org.au> - 2017-01-12 09:10 +0100
      Re: x86-64: Maintain 16-byte stack alignment Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-12 09:10 +0100

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