[Mesa-dev] [PATCH 2/2] gallium/util: libunwind support

[Rob Clark]

On Fri, Apr 7, 2017 at 5:06 AM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
> Hi, Rob,
>
> On 04/04/2017 07:12 PM, Rob Clark wrote:
>> On Tue, Apr 4, 2017 at 12:10 PM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>> On 04/04/2017 05:36 PM, Rob Clark wrote:
>>>> On Tue, Apr 4, 2017 at 10:28 AM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>>>> On 04/04/2017 04:06 PM, Rob Clark wrote:
>>>>>> On Tue, Apr 4, 2017 at 10:00 AM, Rob Clark <robdclark at gmail.com> wrote:
>>>>>>> On Tue, Apr 4, 2017 at 8:45 AM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>>>>>>> On 04/04/2017 02:34 PM, Rob Clark wrote:
>>>>>>>>> On Tue, Apr 4, 2017 at 1:49 AM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>>>>>>>>> But one more worrying thing is that with these fixes, debug_flush gets
>>>>>>>>>> too slow to be usable. I get about one frame every 5 seconds from Ubuntu
>>>>>>>>>> compiz. The culprit seems to be unw_get_proc_name(). Is there a way we
>>>>>>>>>> can save intermediate information during backtrace capture and call this
>>>>>>>>>> function at printout time?
>>>>>>>>> btw, is it common to capture many more backtraces than you print?
>>>>>>>>> (Just to check if defering the unw_get_proc_name() would actually help
>>>>>>>>> anything..)
>>>>>>>> Yes. The debug_flush functionality captures the backtrace on each map in
>>>>>>>> case someone would flush when mapped or try a recursive map. Only then
>>>>>>>> they are printed.
>>>>>>>>
>>>>>>>> FWIW in u_debug_symbol.c, José has implemented a hash table for name
>>>>>>>> lookups. Perhaps one solution would to save the IP and insert the
>>>>>>>> function name in the hash table with the IP as key.
>>>>>>>>
>>>>>>> fwiw, I added a hash-table:
>>>>>>>
>>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_freedreno_mesa_commits_wip-2Dlibunwind&d=DwIFaQ&c=uilaK90D4TOVoH58JNXRgQ&r=wnSlgOCqfpNS4d02vP68_E9q2BNMCwfD2OZ_6dCFVQQ&m=VIINenNexQBSdAAjE5gNpegAuq9f_KOvkScYgqyZchQ&s=imNnOqL2QvjC7ok9q_QrCXSDr6AXpVgK4MYos9ZcyoM&e=
>>>>>>>
>>>>>>> It seems to work, but my hacked up test doesn't collect more
>>>>>>> stacktraces than it prints so haven't really tested it from
>>>>>>> performance standpoint.
>>>>>>>
>>>>>>> Possibly it could re-use debug_symbol_name_cached() instead, or at
>>>>>>> least not duplicate the hashtable..
>>>>>>>
>>>>> So, with your patches including the hash table, I'm up to speed again.
>>>>> But addr2line.sh doesn't work.
>>>>>
>>>> Do you have an example of a stacktrace before addr2line.sh?  I'm
>>>> trying to figure out the regexp's in that script but I guess it would
>>>> be easier if I knew what it was matching against.
>>>>
>>>> BR,
>>>> -R
>>> Here it goes. I think what's translated by addr2line.sh is the part
>>> starting the line up to the closing parentheses. The rest of the line is
>>> let through as it is.
>>>
>> ok, after bashing my head against regexps for a bit, and eventually
>> getting that part working, I realized that the addr2line trick needed
>> relative offset within the DSO.  So we had to diverge a bit from the
>> format used by xserver/weston.  At that point, it was easier to just
>> drop the leading stackframe number so that it works as-is with
>> addr2line.sh
>>
>> I've pushed an extra patch to my wip-libunwind branch to tweak the
>> output to work with addr2line.sh
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_freedreno_mesa_commits_wip-2Dlibunwind&d=DwIFaQ&c=uilaK90D4TOVoH58JNXRgQ&r=wnSlgOCqfpNS4d02vP68_E9q2BNMCwfD2OZ_6dCFVQQ&m=izk41sNzPd9GEwoptJ7x3vK9EgrFWrOdYHqw5_LQ3kU&s=8hv-C4A14nMrGosCL_38GBE1OLHMs3y4V_G5T26B_lc&e=
>>
>> BR,
>> -R
>
> Could you push these to mesa master?
>

ok, done.. I was going to try to look into backtrace() fallback and
fix that warn, but given that I haven't had time to do that yet, and
that those three patches at least improve things, I guess it makes
sense to push as-is.

BR,
-R