llvm dev - Nov 2017 - [LLD] Slow callstacks in gdb

Hi,

for programs linked with lld it's substantially slower to get callstacks
in gdb, in comparison to gold-linked programs. Two measurements:

lld     gold
15 sec  3 sec
6 sec   2 sec

This is a debug build, rather large binaries (lots of templates). I have
seen even worse performance for debug+UBSan builds. I think code size (and
therefore DWARF size) has an impact. Is there some information missing
that gdb needs, and only gold generates?

gdb version is 8. I tested lld 5.0 and an earlier 4.0 trunk version.

Note that these binaries do not use gdb indexing.

Has anyone seen something similar?

Best regards,
Martin
-- 
http://www.productive-cpp.com/

I do not know what is going on with your binary, but I'd first inspect
section sizes. Can you run `readelf --sections` against the two executable
to see if there's significant difference in section size?

On Mon, Nov 27, 2017 at 7:00 AM, Martin Richtarsky <s at martinien.de>
wrote:
> Hi,
>
> for programs linked with lld it's substantially slower to get
callstacks
> in gdb, in comparison to gold-linked programs. Two measurements:
>
> lld     gold
> 15 sec  3 sec
> 6 sec   2 sec
>
> This is a debug build, rather large binaries (lots of templates). I have
> seen even worse performance for debug+UBSan builds. I think code size (and
> therefore DWARF size) has an impact. Is there some information missing
> that gdb needs, and only gold generates?
>
> gdb version is 8. I tested lld 5.0 and an earlier 4.0 trunk version.
>
> Note that these binaries do not use gdb indexing.
>
> Has anyone seen something similar?
>
> Best regards,
> Martin
> --
> http://www.productive-cpp.com/
>
>
>
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Martin Richtarsky via llvm-dev <llvm-dev at lists.llvm.org> writes:
> Hi,
>
> for programs linked with lld it's substantially slower to get
callstacks
> in gdb, in comparison to gold-linked programs. Two measurements:
>
> lld     gold
> 15 sec  3 sec
> 6 sec   2 sec
Are both using --gdb-index? Can you try lld trunk if so?

Is any of the programs you tested open source?

Cheers,
Rafael

Is the program being built by gcc or clang?

Cheers,
Rafael

Rafael Avila de Espindola <rafael.espindola at gmail.com> writes:
> Martin Richtarsky via llvm-dev <llvm-dev at lists.llvm.org> writes:
>
>> Hi,
>>
>> for programs linked with lld it's substantially slower to get
callstacks
>> in gdb, in comparison to gold-linked programs. Two measurements:
>>
>> lld     gold
>> 15 sec  3 sec
>> 6 sec   2 sec
>
> Are both using --gdb-index? Can you try lld trunk if so?
>
> Is any of the programs you tested open source?
>
> Cheers,
> Rafael