Messages in this thread | | | Date | Tue, 21 Jan 2014 10:55:52 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf tools: Fix JIT profiling on heap |
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Em Tue, Jan 21, 2014 at 02:54:32PM +0900, Namhyung Kim escreveu: > On Fri, 17 Jan 2014 11:34:04 -0300, Arnaldo Carvalho de Melo wrote: > > Em Fri, Jan 17, 2014 at 04:44:04PM +0900, Namhyung Kim escreveu: > >> On Thu, 16 Jan 2014 20:23:27 +0000, Gaurav Jain wrote: > >> > Does perf support data mappings from perf map files?
> >> IIUC there's no difference between function and data mapping. So
> > Do the /tmp/perf mapping has any per entry indication on the type of > > symbol it is (data, text) like ELF and kallsyms symtabs have?
> Quoting Documentation/jit-interface.txt:
> Each line has the following format, fields separated with spaces:
> START SIZE symbolname
> > It is possible for a function and a variable to have the same virt > > addrin some arches (SPARC, iirc), that is why we have different MAP_ > > types (FUNCTION, VARIABLE)
> Hmm.. didn't know that, interesting..
> > So a 'struct map' for a data mmap should point to a different 'dso' > > of the JIT /tmp/perf-... style if those maps don't have per entry > > indication of text/data.
> Yes, but there's no way to do it currently.
Why not? Its just a matter of having a /tmp/perf-...-data file that has the same structure as the current files for text mmaps :-)
It would then be used as the map->dso for resolving data addresses.
> >> only function symbols in function mappings and variables in data > >> mapping based on the address it accesses.
> > Well, the lookup should figure out if the IP refers to TEXT or DATA and > > use MAP__{FUNCTION, VARIABLE} accordingly when asking for symbol > > resolution.
> Right. But in this case we cannot determine whether a symbol in the > /tmp/perf-... file is a function or variable.
That is why we would then need to have separate /tmp/perf-... files, disambiguated by an extension, one for text addresses, another for data ones.
Or change the format to match /proc/kallsyms, which probably is what we should've done from day one...
Detecting the format change would be trivial, as we would find 3 tokens in the new format, instead of the current 2.
> >> What I wasn't sure is whether JIT program also produces some dynamic data. > >> And I think only perf mem command cares about data mappings, no?
> > Well, I think it would be great to do that kind of data resolution for > > JITs the same way it is interesting to do for ELF ones :-) > > > > I need to stare harder at that patch, but with the above in mind, do we > > really have to check if the map is MAP__FUNCTION as IIRC this patch > > does? > > Not sure. For a JIT case, I guess the mapping is always executable and > we don't support data mapping yet, so it seems okay for now.
Ok, agreed, applying the patch, thanks,
- Arnaldo
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