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    SubjectRe: [PATCH 1/3] perf events: fix WARN_ON_ONCE for 64-bit raw data, SW events


    On 02/18/11 04:00, Peter Zijlstra wrote:
    > On Thu, 2011-02-17 at 22:53 -0700, David Ahern wrote:
    >> This check does not work out for 64-bit counter:
    >>
    >> sizeof(u32) + sizeof(u64) = 4 + 8 = 12
    >>
    >> which does not pass the WARN_ON_ONCE test. I'm guessing (hoping
    >> really) that the intent is that the size of the raw data is a
    >> multiple of 4 bytes, not 8.
    >
    > No the data must come in 8bytes strides.
    >

    Then the sizeof the size field needs to be moved to u64; right now it is
    u32:

    struct perf_raw_record {
    u32 size;
    void *data;
    };

    So size should be changed to u64 rather than modifying the WARN_ON_ONCE?


    Another gotcha is in perf_output_sample there is:
    struct {
    u32 size;
    u32 data;
    } raw = {
    .size = sizeof(u32),
    .data = 0,
    };

    While that meets the 8-byte stride I was concerned that changing the
    size field to u64 breaks ABI.

    David


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