Re: usability issues with inlining and backtraces

[Milian Wolff <milian.wolff@kdab.com>]

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On Monday, August 15, 2016 11:32:33 AM CEST Milian Wolff wrote:
> On Monday, June 13, 2016 6:07:13 PM CEST Milian Wolff wrote:
> > Ping?
> > 
> > Andi, I'd be very interested in your answers on my questions below. Most
> > notably, `srcline` with `--call-graph ...,address` seems to be highly
> > buggy
> > for me.
> 
> Reping again.
> 
> Andi, or anyone else - I would really appreciate some more feedback on my
> questions below.
> 
> I esp. wonder how to leverage srcline and addresses in the call-graph, as
> that has the potential to greatly increase perf's value to me.

OK, I have found at least two culprits that partially explain the behavior.

On one hand, I'm simply missing debug information for some libraries, such as 
libm, libc etc. pp. Due to that, the addr2line step fails and sym+offset is 
displayed.

On the other hand, there seems to be a bug in perf: 

When hist_entry__get_srcline calls get_srcline I see from debug output

he->ip=307e, sym=main -> rip_obj2dump=40307e -> mandelbrot.h:39

But in callchain_list__sym_name, I see:

cl->ip=40373d, sym=main -> rip_obj2dump=80373d-> main+8390413

So it seems like the callchain_list is missing a normalization step that is 
applied to the IP addresses stored in hist_entry. Can someone point me into 
the right direction?

If I change callchain_list__sym_name to pass cl->ip - cl->ms.map->start to 
map__rip_2objdump this feature works much better for me, but I doubt that this 
is the correct fix.

Thanks
-- 
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

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