Re: cmpxchg and x86 flags output

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: cmpxchg and x86 flags output
Date	2016-06-22 18:40 +0200
Message-ID	<rMTm2-5QR-9@gated-at.bofh.it> (permalink)
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On 06/22/16 09:11, David Howells wrote:
> H. Peter Anvin <hpa@zytor.com> wrote:
> 
>> The question for me is for things like lock patching that we do on x86...
> 
> This might be pertinent to what you're asking:
> 
> 	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70973
> 

I am kind of hesitant to put knowledge of this into gcc, because it
freezes something that currently is not gcc-dependent (although we could
separate out the gcc-generated and non-gcc-generated bits if we really
care.)  With the gcc flags output we can do this with assembly code as
well today (on x86), so it is unclear if we have any compelling reason
to need intrinsics that we won't be able to rely on existing for a long
time (the difference between gcc versions that have flags support and
don't have it has already been abstracted out in the x86/asm branch of
the tip tree, so we don't need two versions.)

	-hpa

Thread

cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-15 02:00 +0200
  Re: cmpxchg and x86 flags output Peter Zijlstra <peterz@infradead.org> - 2016-06-15 11:00 +0200
    Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-17 00:30 +0200
      Re: cmpxchg and x86 flags output David Howells <dhowells@redhat.com> - 2016-06-21 11:10 +0200
        Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-21 19:10 +0200
          Re: cmpxchg and x86 flags output David Howells <dhowells@redhat.com> - 2016-06-22 18:20 +0200
            Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-22 18:40 +0200
              Re: cmpxchg and x86 flags output Linus Torvalds <torvalds@linux-foundation.org> - 2016-06-22 19:20 +0200
                Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-22 20:00 +0200
        Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-21 19:40 +0200
          Re: cmpxchg and x86 flags output "H. Peter Anvin" <hpa@zytor.com> - 2016-06-22 02:40 +0200
            Re: cmpxchg and x86 flags output David Howells <dhowells@redhat.com> - 2016-06-22 18:20 +0200

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