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    SubjectRe: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released
    Date
    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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