profiling Firefox, no perf-<PID>.map file

profiling Firefox, no perf-<PID>.map file

[Giovanni Gherdovich]

Hello,

when profiling firefox with perf (i.e. `perf top` or `perf record`) I
get errors like "Failed to open /tmp/perf-<PID>.map, continuing
without symbols". The perf docs says it has to do with the support for
JIT'ed code (tools/perf/Documentation/jit-interface.txt), which I
guess is produced by firefox' javascript engine (I could be wrong).

The documentation is a bit vague on how to have those perf-<PID>.map
files produced correctly, and the original commit introducing this
feature, 80d496be89ed "perf report: Add support for profiling JIT
generated code" only says "A JIT compiler is required [...]".

Is there a way to profile firefox and get those *.map files?
It's more of a curiosity, I am new to perf and I'm playing around.

Thanks,
Giovanni

Re: profiling Firefox, no perf-<PID>.map file

[Milian Wolff]

[-- Attachment #1: Type: text/plain, Size: 1231 bytes --]

On Samstag, 3. September 2016 20:53:26 CEST Giovanni Gherdovich wrote:
> Hello,
> 
> when profiling firefox with perf (i.e. `perf top` or `perf record`) I
> get errors like "Failed to open /tmp/perf-<PID>.map, continuing
> without symbols". The perf docs says it has to do with the support for
> JIT'ed code (tools/perf/Documentation/jit-interface.txt), which I
> guess is produced by firefox' javascript engine (I could be wrong).
> 
> The documentation is a bit vague on how to have those perf-<PID>.map
> files produced correctly, and the original commit introducing this
> feature, 80d496be89ed "perf report: Add support for profiling JIT
> generated code" only says "A JIT compiler is required [...]".
> 
> Is there a way to profile firefox and get those *.map files?
> It's more of a curiosity, I am new to perf and I'm playing around.

You need integration for generating such a file in the JavaScript engine. node 
and QML are two examples for that. But if you don't want to attribute JIT code 
addresses to JavaScript code, you can safely ignore this warning.

Bye

-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

[-- Attachment #2: smime.p7s --]
[-- Type: application/pkcs7-signature, Size: 5903 bytes --]

Re: profiling Firefox, no perf-<PID>.map file

[Giovanni Gherdovich]

On Sat, 2016-09-03 at 22:37 +0200, Milian Wolff wrote:
> [...]
> 
> You need integration for generating such a file in the JavaScript engine. node 
> and QML are two examples for that. But if you don't want to attribute JIT code 
> addresses to JavaScript code, you can safely ignore this warning.
> 

Right, thanks for pointing it out. It's the VM who's JIT'ing that is
in charge of writing the perf-<PID>.map files.
I've now found the relevant part in Brendan Gregg's perf page describing
this: http://www.brendangregg.com/perf.html#JIT_Symbols
The first time around I read that section it didn't ring a bell,
now I see what the problem is.

Thanks,
Giovanni