[llvm-dev] Need help on identifying a patch which fixed lld on linux platform

[Rui Ueyama via llvm-dev]

On Thu, Jun 13, 2019 at 7:15 PM karnajit wangkhem <karnajitw at gmail.com>
wrote:

> Thanks for the info Rui.
>
> Transitioning from llvm 5.0 to llvm 7.0 will take some time due to the
> nature/process of the production environment. Is it ok to use lld 7.0 with
> llvm 5.0?
>

If you are not doing LTO, then yes, you can use any version of lld with any
version of LLVM or Clang. lld takes the industry-standard file format as
inputs, so you can use lld with any compiler including non-LLVM ones like
GCC.

I'd recommend you do that if you can upgrade lld. The improvements from lld
4.0 to lld 7.0 are significant, since lld 4.0 was not very mature when it
was released.


> On Thu, Jun 13, 2019 at 1:47 PM Rui Ueyama <ruiu at google.com> wrote:
>
>> Looks like Ubuntu 12 was released in 2012, and the most recent version of
>> LLVM is LLVM 8.0.0.
>>
>> LLVM 5.0 is pretty old, and in particular, lld in LLVM 5.0 is extremely
>> outdated. IIUC, the first release of LLVM that includes somewhat usable
>> version of lld is LLVM 4.0, and I wouldn't be surprised that LLVM 5.0 has a
>> lot of bugs.
>>
>> Can't you simply use a newer version of lld?
>>
>> On Thu, Jun 13, 2019 at 4:01 PM karnajit wangkhem via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi All,
>>>
>>> This test is on a ubuntu 12 box. Can anyone please point me what
>>> revision/commit-id of lld fixed this issue which was atleast in llvm 5.0.
>>> .
>>> ├── build.sh
>>> ├── main.c
>>> ├── shared
>>> │   └── sh.c
>>> └── static
>>>     └── st.c
>>>
>>> [[ build.sh ]]
>>>
>>> #!/bin/sh
>>>
>>> CC="${TOOLCHAIN}/bin/clang"
>>> AR="${TOOLCHAIN}/bin/llvm-ar"
>>> CFLAGS="-g -O"
>>> LDFLAGS="-fuse-ld=lld"
>>>
>>> rm shared/sh.o static/st.o main.o
>>> rm shared/libsh.so static/libst.a main
>>>
>>> ${CC} ${CFLAGS} -c shared/sh.c -o shared/sh.o
>>> ${CC} ${CFLAGS} ${LDFLAGS} -shared -o shared/libsh.so shared/sh.o
>>>
>>> ${CC} ${CFLAGS} -c static/st.c -o static/st.o
>>> ${AR} cq static/libst.a static/st.o
>>>
>>> ${CC} ${CFLAGS} -c main.c -o main.o
>>>
>>> ${CC} ${CFLAGS} ${LDFLAGS} -o main -Lshared -lsh -Lstatic -lst  main.o
>>> -Wl,-rpath=shared
>>>
>>> [[ main.c ]]
>>>
>>> void gn();
>>>
>>> int main()
>>> {
>>>     gn();
>>>     return 0;
>>> }
>>>
>>> [[ shared/sh.c ]]
>>>
>>> #include <stdio.h>
>>>
>>> void gn(void);
>>> void fn(void);
>>>
>>> void gn()
>>> {
>>>     printf("Calling gn...\n");
>>>     fn();
>>> }
>>>
>>> [[ static/st.c ]]
>>>
>>> #include <stdio.h>
>>>
>>> void fn(void);
>>>
>>> void fn()
>>> {
>>>     printf("Calling fn...\n");
>>> }
>>>
>>>
>>> Code flow:
>>> main -> gn (shared library) -> fn (part of the static lib)
>>>
>>> Result:
>>> With llvm 5.0
>>>
>>> ./main
>>> Calling gn...
>>> ./main: symbol lookup error: shared/libsh.so: undefined symbol: fn   <==
>>> symbol fn was not found in binary "main"
>>>
>>> readelf -s main | grep fn
>>> <Nothing>
>>>
>>> With llvm 7.0
>>>
>>> ./main
>>> Calling gn...
>>> Calling fn...
>>>
>>> readelf -s main | grep fn
>>>      9: 0000000000001100    12 FUNC    GLOBAL DEFAULT   13 fn
>>>     36: 0000000000001100    12 FUNC    GLOBAL DEFAULT   13 fn
>>>
>>> Regards,
>>> Karan
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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