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

[Masami Hiramatsu]

Hi Arnaldo,

On Thu, 5 Jan 2017 15:47:43 -0300
Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:

> 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@xxxxxxxxxx> wrote:
> > > > [acme@jouet linux]$ grep e1000_xmit_frame /proc/kallsyms 
> > > > ffffffffc046fc10 t e1000_xmit_frame	[e1000e]
> > > > [acme@jouet 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)

I've found an issue on perf kallsyms. Please see below.

When I run kallsyms without root privilege, it works well.

$ ./perf kallsyms -vv drm_malloc_ab
Failed to open /proc/kcore. Note /proc/kcore requires CAP_SYS_RAWIO capability to access.
drm_malloc_ab: [i915] /lib/modules/4.8.15-300.fc25.x86_64/kernel/drivers/gpu/drm/i915/i915.ko.xz 0xffffffffc0211950-0xffffffffc02119a6 (0x309c0-0x30a16)

However, with root privilege it failed to get correct module name...

$ sudo ./perf kallsyms -vv drm_malloc_ab
Using /proc/kcore for kernel object code
drm_malloc_ab: [kernel] /proc/kcore 0xffffffffc0211950-0xffffffffc02119b0 (0x7fffc0214950-0x7fffc02149b0)

Thank you,


> 
> - Arnaldo


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>