On 05/28/2014 11:55 AM, Peter Zijlstra wrote:
> On Wed, May 28, 2014 at 11:45:04AM +0300, Adrian Hunter wrote:
>> perf tools like 'perf report' can aggregate samples by comm
>> strings, which generally works. However, there are other
>> potential use-cases. For example, to pair up 'calls'
>> with 'returns' accurately (from branch events like Intel BTS)
>> it is necessary to identify whether the process has exec'd.
>> Although a comm event is generated when an 'exec' happens
>> it is also generated whenever the comm string is changed
>> on a whim (e.g. by prctl PR_SET_NAME). This patch adds a
>> flag to the comm event to differentiate one case from the
>> other.
>>
>> In order to determine whether the kernel supports the new
>> flag, a selection bit named 'exec' is added to struct
>> perf_event_attr. The bit does nothing but will cause
>> perf_event_open() to fail if the bit is set on kernels
>> that do not have it defined.
>>
>
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -302,8 +302,8 @@ struct perf_event_attr {
>> exclude_callchain_kernel : 1, /* exclude kernel
>> callchains */
>> exclude_callchain_user : 1, /* exclude user
>> callchains */
>> mmap2 : 1, /* include mmap with inode
>> data */
>> -
>> - __reserved_1 : 40;
>> + exec : 1, /* flag comm events that
>> are due to an exec */
>> + __reserved_1 : 39;
>>
>
> Yah.. that's just sad :-(
>
> the only capabilities mask we have is in the mmap() page, so without
> mmap()ing we have no way to test that.
>
> Would it make sense to call it comm_exec?
Yes, that is better. Do you want me to resend the patch?
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