[llvm-dev] can valgrind read LLD's debug info?

Andrew Kelley via llvm-dev llvm-dev at lists.llvm.org
Thu Apr 5 14:49:38 PDT 2018


Confirmed that -no-rosegment worked around the issue.

However, a valgrind developer says that perhaps LLD is generating strange
object files:

<tomhughes> I suspect that is some extra ro segment in addition to the
normal rodata
<tomhughes> so without it you have two
<tomhughes> but I know nothing about lld
<tomhughes> but without an executable to examine/test it's hard to be sure
<andrewrk> the not working elf file has only 1 .rodata section
<andrewrk> here's the difference between bad and good headers:
https://clbin.com/vvB8O
<tomhughes> ah I see it's because it's a mapped ro segment in the phdrs
<tomhughes> don't think it's the problem but this file is quite odd - the
ro segment in the phdrs doesn't seem to have to any section listed in the
shdrs
<tomhughes> s/have/map/

Is this something where LLD can be reasonably changed to be compatible with
valgrind without this workaround?

Thanks,
Andrew

On Thu, Apr 5, 2018 at 5:28 PM, Andrew Kelley <superjoe30 at gmail.com> wrote:

> As a frontend, what are the downsides of enabling --no-rosegment by
> default?
>
> So far the pro list is:
>  * valgrind debug info will work by default
>
> What's on the con list?
>
> On Thu, Apr 5, 2018 at 5:16 PM, Shoaib Meenai <smeenai at fb.com> wrote:
>
>> It's more of a valgrind issue than an LLD issue, but you can work around
>> it by linking with --no-rosegment
>>
>>
>>
>> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Andrew
>> Kelley via llvm-dev <llvm-dev at lists.llvm.org>
>> *Reply-To: *Andrew Kelley <superjoe30 at gmail.com>
>> *Date: *Thursday, April 5, 2018 at 2:14 PM
>> *To: *LLVM Dev <llvm-dev at lists.llvm.org>
>> *Subject: *[llvm-dev] can valgrind read LLD's debug info?
>>
>>
>>
>> I just filed https://bugs.llvm.org/show_bug.cgi?id=37021
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D37021&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=LOIzu9sn31pmykUwYH1_wAigCpxv33qUDNdmOrmGop4&s=2_EmscX6fjQZR0pF1CQWKUPDgpBLCJhFfnOvlkivJBE&e=>
>>
>> There was another bug that seems related to this which is
>> https://bugs.llvm.org/show_bug.cgi?id=35032
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D35032&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=LOIzu9sn31pmykUwYH1_wAigCpxv33qUDNdmOrmGop4&s=c8bjnWV_NwOLITc1Tc5dCjJC88BhCt86girLjAbXTbk&e=>
>> but that one is marked fixed. But this seems to be an issue in trunk.
>>
>> Is this a known issue?
>>
>
>
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