Re: bfd_find_inliner_info reports different (wrong) information compared to GDB - off-by-one?

[Milian Wolff <mail at milianw dot de>]

On Mittwoch, 5. Oktober 2016 22:22:34 CEST Mark Wielaard wrote:
> Hi Milian,
> 
> On Wed, 2016-10-05 at 17:45 +0200, Milian Wolff wrote:
> > I'm trying to improve Linux perf report by adding inliner information to
> > the callstacks it reports, to make the output more easily interpretable
> > when looking at complicated C++ applications.
> 
> You might want to take a look at eu-stack (src/stack.c) in elfutils
> which does this too. If you are using the elfutils libraries (libdw.so).

<snip, and reordered>

> I don't know what gdb exactly displays as address in that backtrace.
> It might display the return address, in which case subtracting 1 is the
> right thing to do on x86_64 (that would be an approximation of the call
> address, which is what you want).
> 
> And in fact that is what eu-stack does:
> 
> (gdb) gcore test.core
> Saved corefile test.core
> 
> $ eu-stack -v --core test.core --exec test
> PID 32623 - core
> TID 32623:
> #0  0x00007ffff77f8cf0     __hypot - libm.so.6
>     /usr/src/debug/glibc-2.17-c758a686/math/w_hypot.c:23
> #1  0x0000000000400824 - 1 __complex_abs - test
>     /usr/include/c++/4.8.2/complex:587
> #2  0x0000000000400824 - 1 abs<double> - test
>     /usr/include/c++/4.8.2/complex:595
> #3  0x0000000000400824 - 1 main - test
>     /tmp/test.cpp:14
> #4  0x00007ffff721db35 - 1 __libc_start_main - libc.so.6
>     ../csu/libc-start.c:274
> #5  0x000000000040088f - 1 _start - test

Thanks, I have had a look at the sources and found the code for the adjustion:

      Dwarf_Addr pc = frames->frame[nr].pc;
      bool isactivation = frames->frame[nr].isactivation;
      Dwarf_Addr pc_adjusted = pc - (isactivation ? 0 : 1);

The isactivation information comes from dwfl_frame_pc, so that should be all I 
need to use this properly in Linux perf - thanks!

> > I have a proof of concept locally using bfd_find_inliner_info
> 
> I don't know what bfd_find_inliner_info is.
> It sound like something from binutils?

Oh, indeed - I mixed up the two. Sorry for that, and thanks a lot for still 
helping me out. I will check whether using dwfl instead of bfd for this 
purpose may be advantageous.

Cheers

-- 
Milian Wolff
mail@milianw.de
http://milianw.de

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