Re: [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:

quoted

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