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Re: [Libunwind-devel] unw_step in ARM?

From: Zoltan Kuscsik
Subject: Re: [Libunwind-devel] unw_step in ARM?
Date: Tue, 23 Oct 2012 12:06:09 +0200


using --unwind-tables should also do the trick. It is  more lightweight  than -g
if you just need the unwind information.



On Tue, Oct 23, 2012 at 11:42 AM, Harald Servat <address@hidden> wrote:
> Hello,
> El dt 23 de 10 de 2012 a les 12:33 +0300, en/na Tommi Rantala va
> escriure:
>> 2012/10/23 Harald Servat <address@hidden>:
>> > Hello,
>> >
>> >   I'm using libunwind 1.1 in a Linux with ARM processor. I've found that
>> > unw_step seems not to work, or at least not as in x86-64 because it does
>> > not report all the backtrace but only the top of the stack level. I'm
>> > attaching a simple program (derived from the tests  Gtest-bt.c) that
>> > shows this and also the output in a ARM and in a X86/64 machine.
>> >
>> >   Do I need to compile something in a special way? I've looked at the
>> > objdump -D output from the ARM version and the subroutines seem to be
>> > there.
>> Greetings,
>> Here are some debugging hints:
>> - Try compiling your program with "-g", so that the binary will also
>> carry the dwarf debugging information that is used for backtracing.
>> - Try compiling your program with "-funwind-tables", to get ARM unwind
>> tables that can be alternatively used for backtracing.
>> - There's also a third backtracing alternative on ARM, the frame chain
>> following. You'll need to compile with ARM & APCS modes for it to
>> work.
>> - To see what's happening inside libunwind, configure it with
>> "--enable-debug", then "export UNW_DEBUG_LEVEL=99" before running your
>> program.
>> - On ARM, you can runtime select which unwind method(s) to use via
>> environment variable UNW_ARM_UNWIND_METHOD, valid choices from
>> include/tdep-arm/libunwind_i.h (by default, libunwind tries them all):
>> #define UNW_ARM_METHOD_ALL          0xFF
>> #define UNW_ARM_METHOD_DWARF        0x01
>> #define UNW_ARM_METHOD_FRAME        0x02
>> #define UNW_ARM_METHOD_EXIDX        0x04
>   Adding the -g did the trick. Now the sample works fine!
>   I used it to exemplify an issue I'm having with a largest application
> we're building. I'll rebuild this large application with -g and see if
> it works.
>   Thank you Tommi!
>> Regards,
>> Tommi Rantala
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