Groups > linux.kernel > #1193590

Re: ASM flags in general

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: ASM flags in general
Date	2015-07-28 01:40 +0200
Message-ID	<pR09Z-8vE-45@gated-at.bofh.it> (permalink)
References	(1 earlier) <pQVWF-2rE-9@gated-at.bofh.it> <pQXlN-4tq-41@gated-at.bofh.it> <pQXOO-5h8-19@gated-at.bofh.it> <pQZnA-7lN-31@gated-at.bofh.it> <pR09Z-8vE-47@gated-at.bofh.it>
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On Mon, Jul 27, 2015 at 4:22 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> For that to work, gcc would have to know about the extable.

It could, I think:

asm goto (
    "1: mov ...\n\t"
    _ASM_EXTABLE(1b, %l2)  /* or whatever index it is */
    : ... : ... : ... : efault);

return 0;

efault:
     return -EFAULT;

I think that wrmsr_safe could get this treatment with current GCC.
put_user plausibly could, too, if we were willing to mark it volatile
and accept that we're lying a little bit about the lack of an output
constraint.  get_user would need GCC to understand output constraints
for real.

--Andy
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Thread

Re: ASM flags in general Andy Lutomirski <luto@amacapital.net> - 2015-07-28 00:50 +0200
  Re: ASM flags in general Andy Lutomirski <luto@amacapital.net> - 2015-07-28 01:40 +0200
    Re: ASM flags in general "H. Peter Anvin" <hpa@zytor.com> - 2015-07-28 02:00 +0200
      Re: ASM flags in general Andy Lutomirski <luto@amacapital.net> - 2015-07-28 02:00 +0200
        Re: ASM flags in general "H. Peter Anvin" <hpa@zytor.com> - 2015-07-28 02:10 +0200
        Re: ASM flags in general "H. Peter Anvin" <hpa@zytor.com> - 2015-07-28 02:40 +0200
          Re: ASM flags in general Andy Lutomirski <luto@amacapital.net> - 2015-07-28 02:50 +0200
    Re: ASM flags in general Andy Lutomirski <luto@amacapital.net> - 2015-07-28 02:00 +0200

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