Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

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From: H. Peter Anvin
Date: Wednesday, July 14, 2010 - 12:00 pm

On 07/14/2010 11:18 AM, H.J. Lu wrote:

Not directly as far as I can tell.

The issue is if gcc can ever reorder, duplicate or elide a volatile
operation (either asm volatile or a volatile-annotated memory
reference.)  In my (and Linus') opinion, this would be an incredibly
serious bug.

The gcc 4.4 issue, which is separate from the definition issue, is that
it seems to assume that it can elide references to "const volatile"
objects.  "const volatile" should mean a value that could change at any
time but which is a bug to write to -- for example a readonly hardware
register.

	-hpa

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Messages in current thread:
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 13, 11:21 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 13, 4:49 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:19 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:34 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:57 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 11:15 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., H. Peter Anvin, (Wed Jul 14, 12:00 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 1:40 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 1:58 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 27, 10:46 am)
xchg() and cmpxchg(), H. Peter Anvin, (Tue Jul 27, 4:57 pm)
[tip:x86/urgent] x86: Add memory modify constraints to xch ..., tip-bot for H. Peter ..., (Tue Jul 27, 10:33 pm)
[tip:x86/asm] x86, asm: Clean up and simplify <asm/cmpxchg.h>, tip-bot for H. Peter ..., (Wed Jul 28, 4:28 pm)
[tip:x86/asm] x86, asm: Move cmpxchg emulation code to arc ..., tip-bot for H. Peter ..., (Thu Jul 29, 1:12 pm)
[tip:x86/asm] x86, asm: Merge cmpxchg_486_u64() and cmpxch ..., tip-bot for H. Peter ..., (Thu Jul 29, 1:13 pm)
Re: [tip:x86/urgent] x86: Add memory modify constraints to ..., Jeremy Fitzhardinge, (Mon Aug 2, 4:51 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Thu Sep 9, 12:53 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Thu Sep 9, 2:09 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Fri Sep 10, 6:10 am)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Fri Sep 24, 12:17 am)