Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released | Date | Fri, 22 Aug 2008 11:37:50 +1000 |
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On Friday 22 August 2008 07:06, Jeremy Fitzhardinge wrote: > Nick Piggin wrote: > > On Thursday 21 August 2008 22:26, jmerkey@wolfmountaingroup.com wrote: > >> I used the smp_wmb() functions. I noted a couple of things. a) some of > >> these macros just emit __asm__ __volatile__ into the code so why not > >> just say "volatile" to begin with > > > > It is not the same as volatile type. What it does is tell the compiler > > to clobber all registers or temporaries. This something pretty well > > defined and hard to get wrong compared to volatile type. > > No, that's not what "asm volatile" means. Its *only* meaning is "emit > this, even if it doesn't look like it has side-effects and its results > are not used". An asm() with no outputs is "volatile" by default, which > makes most of the uses of "asm volatile" in the kernel redundant. "asm > volatile" also has no effect on the ordering of the asm with respect to > other code; you must use constraints to do that. > > An asm with a "memory" clobber is sufficient to make sure that gcc > doesn't cache memory values in registers; perhaps that's what you mean.
That is what I meant, yes.
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