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

[Rui Ueyama via llvm-dev]

--rosegment puts read-only data and executable text in a single segment and
make it executable, so your read-only code becomes executable. I think that
shouldn't be a default behavior. If valgrind needs that, we can't fix it by
changing the default.

On Thu, Apr 5, 2018 at 2:50 PM Andrew Kelley via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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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