Re: [Libunwind-devel] unw_backtrace(): Performance slowdown for ARM?

[Luke Diamand]

On 17 January 2018 at 15:55, Dave Watson <address@hidden> wrote:
>> > I didn't notice anything in particular looking at the commit logs.
>> > I'll try and repro when I get a chance
>>
>> arm_find_proc_info() seems to start out trying eh_frame tables. Isn't
>> it always best on ARM to start looking in the exidx tables?
>
> Sounds reasonable to me, although I'm not an arm expert.  Did the
> default change somewhere?  I couldn't find anything looking at the
> history.

I'm definitely not an expert!

But the exidx tables are quite a bit smaller than the DWARF tables: on
the code I'm working on, I see ~2MB on the MIPS target vs ~0.5MB on
the ARM target for the unwind tables. And I don't think there's even
an option in gcc to choose anything else.

And this presentation by Linaro (who _are_ experts!) says "Unwinding
on ARM is different - no .eh_frame but .ARM.exidx and .ARM.extab".

https://wiki.linaro.org/KenWerner/Sandbox/libunwind?action=AttachFile&do=get&target=libunwind-LDS.pdf