llvm dev - May 2021 - libunwind, -static and -lpthread on ARM

Hello,

I'm trying to cross compile an executable that's using pthread. Target
is
armv7-linux-gnueabihf. I'm using the latest raspberry pi os as sysroot.
I've managed to successfully build llvm, clang + all the runtimes and
I'm
trying to build a statically linked executable that's using as less GNU
stuff as possible.

clang++ -sysroot=...  -stdlib=libc++ --rtlib=compiler-rt -static
-resource-dir ... -fuse-ld=lld -lc++abi -lunwind test.cpp

The linker error I'm getting is:

ld.lld: error: undefined symbol: _Unwind_ForcedUnwind
>>> referenced by unwind.c:121
>>>               unwind.o:(__pthread_unwind) in archive
path-to-sysroot/usr/lib/arm-linux-gnueabihf/libpthread.a

Peeking at libunwind's internals, it seems clear there's no
_Unwind_ForcedUnwind built for ARM (at least not with default options).
What options do I have?

1) Should I add some options when building libunwind so I get
_Unwind_ForcedUnwind? I'm not sure this is even possible
2) Use libgcc?

Thanks,
Andrei
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Hello,
I may be wrong here but i was getting something like this in old vers of
clang.

Id assume, pthread.a namely unwind.c is using api for unwinding thats
incompatible with one provided by clang libs. Prolly assumed gcc model or
windows api. Id check source of unwind.c and lookup+use or if absent
implement exception api version thats compatible with clang. We will need
to ask somebody else which clang lib provides this api. Documentation to
clang might have some hints too.

Best regards,
Pawel

sob., 1.05.2021, 03:47 użytkownik Andrei Datcu via llvm-dev <
llvm-dev at lists.llvm.org> napisał:
> Hello,
>
> I'm trying to cross compile an executable that's using pthread.
Target is
> armv7-linux-gnueabihf. I'm using the latest raspberry pi os as sysroot.
> I've managed to successfully build llvm, clang + all the runtimes and
I'm
> trying to build a statically linked executable that's using as less GNU
> stuff as possible.
>
> clang++ -sysroot=...  -stdlib=libc++ --rtlib=compiler-rt -static
> -resource-dir ... -fuse-ld=lld -lc++abi -lunwind test.cpp
>
> The linker error I'm getting is:
>
> ld.lld: error: undefined symbol: _Unwind_ForcedUnwind
> >>> referenced by unwind.c:121
> >>>               unwind.o:(__pthread_unwind) in archive
> path-to-sysroot/usr/lib/arm-linux-gnueabihf/libpthread.a
>
> Peeking at libunwind's internals, it seems clear there's no
> _Unwind_ForcedUnwind built for ARM (at least not with default options).
> What options do I have?
>
> 1) Should I add some options when building libunwind so I get
> _Unwind_ForcedUnwind? I'm not sure this is even possible
> 2) Use libgcc?
>
> Thanks,
> Andrei
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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