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

Martin Richtarsky <s at martinien.de> writes:
> Rafael Avila de Espindola wrote :
>>> Maybe gdb needs to fall back to slower line number resolution
because
>>> e.g.
>>> low and high bounds cannot be retrieved and debug_line_address is
0?
>>
>> It is hard to know without a reproducible. I tried gdb on clang itself
>> build with both clang and gcc and linked with gold and lld. I could not
>> reproduce the slowdown, but I was using trunk lld.
>
> I will retry with clang trunk, when it reproduces I will build some other
> large project (that has DSOs) using our compile/link options (they are not
> that special, I think).
If you can try lld trunk too that would be awesome.

Cheers,
Rafael

Rafael Avila de Espindola wrote:
>> I will retry with clang trunk, when it reproduces I will build some
>> other
>> large project (that has DSOs) using our compile/link options (they are
>> not
>> that special, I think).
>
> If you can try lld trunk too that would be awesome.
I meant lld trunk :)

The problem goes away when building with clang 4.0 and linking with lld (a
version from trunk maybe 6 weeks before the 5.0.0 release). However the
compile options are different in that case, e.g. with respect to -Ox and
-gx, so it's perhaps a bit apples to oranges.

When building with gcc 6.2.1 and linking with lld trunk, I get a link error:

bin-lld/ld: error: lib/libse.a(file1.cpp.o): unaligned data

What would be helpful to diagnose this?

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

Martin Richtarsky <s at martinien.de> writes:
> Rafael Avila de Espindola wrote:
>>> I will retry with clang trunk, when it reproduces I will build some
>>> other
>>> large project (that has DSOs) using our compile/link options (they
are
>>> not
>>> that special, I think).
>>
>> If you can try lld trunk too that would be awesome.
>
> I meant lld trunk :)
>
> The problem goes away when building with clang 4.0 and linking with lld (a
> version from trunk maybe 6 weeks before the 5.0.0 release). However the
> compile options are different in that case, e.g. with respect to -Ox and
> -gx, so it's perhaps a bit apples to oranges.
>
> When building with gcc 6.2.1 and linking with lld trunk, I get a link
error:
>
> bin-lld/ld: error: lib/libse.a(file1.cpp.o): unaligned data
That means that file1.cpp.o has an invalid sh_offset. Can you post a
readelf -SW of it? How is it being created?

The error is from ELF.h: ELFFile<ELFT>::getSectionContentsAsArray.

Cheers,
Rafael