Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily | KernelTrap

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily

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From: Benjamin Herrenschmidt

Subject: Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily

Date: Tuesday, July 24, 2007 - 2:52 am

On Mon, 2007-07-23 at 10:55 -0700, Linus Torvalds wrote:
quoted text> > The goal is to let gcc generate good, beautiful, optimized code.
> 
> No. The point is to let gcc generate *correct* code.
> 
> It's either "=m" together with "memory", or it's "+m".

In fact, it's more than that... the bitops that return a value are often
used to have hand-made spinlock semantics. I'm sure we would get funky
bugs if loads or stores leaked out of the locked region. I think a full
"memory" clobber should be kept around for those cases.

(That's also why on ppc, we give them a few more barriers)

Ben.

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[PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 1/8] i386: bitops: Update/correct comments, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 4/8] i386: bitops: Kill volatile-casting of memory ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 5/8] i386: bitops: Contain warnings fallout from th ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 6/8] i386: bitops: Don't mark memory as clobbered u ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 7/8] i386: bitops: Kill needless usage of __asm__ _ ..., Satyam Sharma, (Mon Jul 23, 9:06 am)

[PATCH 8/8] i386: bitops: smp_mb__{before, after}_clear_bi ..., Satyam Sharma, (Mon Jul 23, 9:06 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 9:10 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Mon Jul 23, 9:13 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 9:18 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 9:21 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 9:22 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 9:23 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 9:26 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 9:30 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 9:32 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Mon Jul 23, 9:33 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Jan Hubicka, (Mon Jul 23, 9:36 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Andi Kleen, (Mon Jul 23, 9:37 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 9:43 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 10:12 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Satyam Sharma, (Mon Jul 23, 10:15 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 10:39 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Linus Torvalds, (Mon Jul 23, 10:46 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Jeremy Fitzhardinge, (Mon Jul 23, 10:49 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Linus Torvalds, (Mon Jul 23, 10:52 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Mon Jul 23, 10:55 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Linus Torvalds, (Mon Jul 23, 10:57 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:05 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 11:07 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 11:14 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 11:28 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:28 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 11:32 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:39 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 11:52 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Trent Piepho, (Mon Jul 23, 1:29 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 1:40 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Trent Piepho, (Mon Jul 23, 2:06 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 2:30 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Nicholas Miell, (Mon Jul 23, 2:48 pm)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Mon Jul 23, 8:53 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Mon Jul 23, 8:57 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Mon Jul 23, 9:19 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Satyam Sharma, (Mon Jul 23, 11:23 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 11:38 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Tue Jul 24, 12:16 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 12:24 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 12:34 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Jeremy Fitzhardinge, (Tue Jul 24, 12:48 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 1:20 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Tue Jul 24, 1:29 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 1:31 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trent Piepho, (Tue Jul 24, 1:38 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 1:39 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 2:21 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, David Howells, (Tue Jul 24, 2:22 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., David Howells, (Tue Jul 24, 2:44 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:49 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:52 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Tue Jul 24, 3:02 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 3:25 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 4:10 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 4:32 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 4:45 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 5:01 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Linus Torvalds, (Tue Jul 24, 10:12 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Linus Torvalds, (Tue Jul 24, 10:20 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 10:24 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Jeff Garzik, (Tue Jul 24, 10:39 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 10:42 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 11:13 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 11:28 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 12:01 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 12:39 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 1:08 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Tue Jul 24, 1:37 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Jeremy Fitzhardinge, (Tue Jul 24, 2:31 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:36 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:37 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 2:46 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 2:55 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 3:32 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 9:10 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Tue Jul 24, 9:54 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trent Piepho, (Wed Jul 25, 6:07 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Wed Jul 25, 6:18 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Wed Jul 25, 6:22 pm)

Re: [PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize, Denis Vlasenko