[llvm-dev] lld + ThinLTO + fprofile-generate causes duplicate symbol errors

[Teresa Johnson via llvm-dev]

Adding Peter to comment on the linker resolution issue.

>From adding save-temps, it looks like lld and gold are giving different
resolutions to the symbols, which is presumably creating this issue:

(first file is with lld and second is with gold)

$ diff a.out.resolution.txt gold/
4c4
< -r=a.o,__llvm_profile_raw_version,plx
---
> -r=a.o,__llvm_profile_raw_version,l
8,9c8,9
< -r=b.o,__llvm_profile_raw_version,x
< -r=b.o,__llvm_profile_filename,x
---
> -r=b.o,__llvm_profile_raw_version,l
> -r=b.o,__llvm_profile_filename,l

I.e. with lld they are all marked as exported.

Peter, any ideas?

Teresa


On Wed, May 9, 2018 at 9:52 AM Teresa Johnson <tejohnson at google.com> wrote:

> Sorry, operator error. I can reproduce now. Interestingly, this does not
> reproduce using gold, and they utilize the same underlying LTO API. Let me
> dig a little using save-temps and see where they diverge.
> Teresa
>
> On Wed, May 9, 2018 at 9:28 AM Pirama Arumuga Nainar <pirama at google.com>
> wrote:
>
>> LLD revision is r331862.  To add, I had initially tried it on r328903,
>> which also reproduced the issue.
>>
>> On Wed, May 9, 2018 at 9:26 AM Pirama Arumuga Nainar <pirama at google.com>
>> wrote:
>>
>>> Hi Teresa,
>>>
>>> Thanks for looking into this.  I hadn't initially tried ToT, but it
>>> reproduces in ToT as well when I tried.
>>>
>>> $ ./clang --version
>>>
>>> clang version 7.0.0 (trunk 331879) (llvm/trunk 331888)
>>> Target: x86_64-unknown-linux-gnu
>>> Thread model: posix
>>> InstalledDir: /ssd2/pirama/llvm-upstream/llvm-release/bin/.
>>>
>>> $ ./ld.lld --version
>>> LLD 7.0.0 (https://git.llvm.org/git/lld.git dc4977e104c7f33758ac6119d1528aafcd8a94dc) (compatible with GNU linkers)
>>>
>>>
>>> On Wed, May 9, 2018 at 6:44 AM Teresa Johnson <tejohnson at google.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Wed, May 9, 2018 at 6:43 AM Teresa Johnson <tejohnson at google.com>
>>>> wrote:
>>>>
>>>>> Hi Pirama,
>>>>>
>>>>> I can't reproduce with either lld or gold, using a compiler built from
>>>>> head. What version is your clang?
>>>>>
>>>> (and your lld)
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> Teresa
>>>>>
>>>>> On Tue, May 8, 2018 at 7:50 PM Pirama Arumuga Nainar via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> The duplicate symbol errors are for __llvm_profile_filename and __llvm_profile_raw_version.
>>>>>> IIUC, these are supposed to be weak symbols but Thin LTO seems to break
>>>>>> this in some way.  This does't happen with gold or no LTO or full
>>>>>> LTO.
>>>>>>
>>>>>> $ cat > a.c
>>>>>> extern int foo();
>>>>>>
>>>>>> int main() {
>>>>>>   return foo();
>>>>>> }
>>>>>>
>>>>>> $ cat > b.c
>>>>>> int foo() {
>>>>>>   return 0;
>>>>>> }
>>>>>>
>>>>>> $ clang a.c -fprofile-generate -flto=thin -c
>>>>>> $ clang b.c -fprofile-generate -flto=thin -c
>>>>>> $ clang a.o b.o -fprofile-generate -flto=thin -fuse-ld=lld
>>>>>> ld.lld: error: duplicate symbol: __llvm_profile_filename
>>>>>> >>> defined at a.c
>>>>>> >>>            lto.tmp:(__llvm_profile_filename)
>>>>>> >>> defined at b.c
>>>>>> >>>            lto.tmp:(.rodata.__llvm_profile_filename+0x0)
>>>>>>
>>>>>> ld.lld: error: duplicate symbol: __llvm_profile_raw_version
>>>>>> >>> defined at a.c
>>>>>> >>>            lto.tmp:(__llvm_profile_raw_version)
>>>>>> >>> defined at b.c
>>>>>> >>>            lto.tmp:(.rodata.__llvm_profile_raw_version+0x0)
>>>>>> clang-7: error: linker command failed with exit code 1 (use -v to see
>>>>>> invocation)
>>>>>> Makefile:10: recipe for target 'a.out' failed
>>>>>> make: *** [a.out] Error 1
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>>>>  408-460-2413
>>>>>
>>>>
>>>>
>>>> --
>>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>>>  408-460-2413
>>>>
>>>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>  408-460-2413
>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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