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

David Ahern
2011-02-18T14:33:31Z

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