[lkml]   [2008]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released
    Nick Piggin wrote:
    > On Thursday 21 August 2008 22:26, 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.


     \ /
      Last update: 2008-08-21 23:09    [W:0.023 / U:43.700 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site