* Peter Zijlstra <[email protected]> wrote:
> On Wed, May 28, 2014 at 12:08:57PM +0300, Adrian Hunter wrote:
> > 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?
>
> Nah, I'll frob it. Thanks!
FYI, this patch breaks pretty much every non-x86 architecture:
/home/mingo/tip/fs/exec.c: In function 'setup_new_exec':
/home/mingo/tip/fs/exec.c:1113: error: implicit declaration of function
'perf_event_exec'
make[2]: *** [fs/exec.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [fs] Error 2
make[1]: *** Waiting for unfinished jobs....
Thanks,
Ingo
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