linux-kernel - Re: [PATCH perf/core 3/3] perf-probe: Fix to probe on gcc generated functions in modules

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Message-ID: <20170105184743.GO27864@kernel.org>
Date:   Thu, 5 Jan 2017 15:47:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH perf/core 3/3] perf-probe: Fix to probe on gcc generated
 functions in modules

Em Thu, Jan 05, 2017 at 12:30:37PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Jan 05, 2017 at 08:20:19PM +0900, Masami Hiramatsu escreveu:
> > On Wed, 4 Jan 2017 11:48:56 -0300
> > Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > > [acme@...et linux]$ grep e1000_xmit_frame /proc/kallsyms 
> > > ffffffffc046fc10 t e1000_xmit_frame	[e1000e]
> > > [acme@...et linux]$ 

> > OK, it sounds reasonable to me too. BTW, how can I get the map for kallsyms?
> > May machine__findnew_module_map(host_machine, ,"[kernel.kallsyms]")
> > include module symbols too?

> Probably what you want is:
 
>  symbol = machine__find_kernel_function_by_name(machine, name, &map);
 
> Then, if symbol is not NULL, map->dso->name will have your module name,
> map->dso->long_name will have the .ko path, etc.

Take a look at 'perf kallsyms' a simple toy cmd that exercises the APIs
you need:

https://git.kernel.org/cgit/linux/kernel/git/acme/linux.git/commit/?h=perf/core&id=25c92235676d2655e3f31ffe02bd4355d838e5e9

Basically:

  struct machine *machine = machine__new_kallsyms();
  struct map *map;
  struct symbol *symbol = machine__find_kernel_function_by_name(machine, symbol_name, &map);

  Then you have symbol->{addr,end,name,etc} and map->dso->{long,short}_name

  $ perf kallsyms e1000_xmit_frame usb_stor_set_xfer_buf
  e1000_xmit_frame: [e1000e] /lib/modules/4.9.0+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko 0xffffffffc046fc10-0xffffffffc0470bb0 (0x19c80-0x1ac20)
  usb_stor_set_xfer_buf: [usb_storage] /lib/modules/4.9.0+/kernel/drivers/usb/storage/usb-storage.ko 0xffffffffc057aea0-0xffffffffc057af19 (0xf10-0xf89)

- Arnaldo