Carl Dong writes:

> Hi all,
>
> Our clang toolchain seems to be quite broken at this time. In particular, it
> fails to call `ld` in the right way such that the startfiles are picked up:
>
> --8<---------------cut here---------------start------------->8---
> $ guix environment --pure --container --ad-hoc clang@6 binutils -- clang++ -v -Xlinker --verbose
> ...
> "/gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/bin/ld"
> 	--eh-frame-hdr
> 	-m elf_x86_64
> 	-dynamic-linker /lib64/ld-linux-x86-64.so.2
> 	-o a.out
> 	crt1.o
> 	crti.o
> 	/gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/crtbegin.o
> 	-L/gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0
> 	-L/gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/../../..
> 	-L/gnu/store/zki2b9r9lkdxnb23sqc8xs99xs9s5x03-clang-6.0.1/bin/../lib
> 	--verbose
> 	-L/gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/lib
> 	-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
> 	/gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/crtend.o
> 	crtn.o
> ...
> attempt to open crt1.o failed
> /gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/bin/ld: cannot find crt1.o: No such file or directory
> attempt to open crti.o failed
> /gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/bin/ld: cannot find crti.o: No such file or directory
> ...
> attempt to open /gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/libm.so failed
> attempt to open /gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/libm.a failed
> attempt to open /gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/../../../libm.so failed
> attempt to open /gnu/store/64xzk1kwk30n7arqgmxs2qy7wzcnc8i3-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/../../../libm.a failed
> attempt to open /gnu/store/zki2b9r9lkdxnb23sqc8xs99xs9s5x03-clang-6.0.1/bin/../lib/libm.so failed
> attempt to open /gnu/store/zki2b9r9lkdxnb23sqc8xs99xs9s5x03-clang-6.0.1/bin/../lib/libm.a failed
> attempt to open /gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/lib/libm.so failed
> attempt to open /gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/lib/libm.a failed
> attempt to open /gnu/store/mx2bgrpxkbdjsmhlxp9a30hbzcilk4cn-binutils-2.32/x86_64-unknown-linux-gnu/lib64/libm.so failed
> attempt to open /gnu/store/mx2bgrpxkbdjsmhlxp9a30hbzcilk4cn-binutils-2.32/x86_64-unknown-linux-gnu/lib64/libm.a failed
> attempt to open /no-ld-lib-path/libm.so failed
> attempt to open /no-ld-lib-path/libm.a failed
> attempt to open /gnu/store/mx2bgrpxkbdjsmhlxp9a30hbzcilk4cn-binutils-2.32/x86_64-unknown-linux-gnu/lib/libm.so failed
> attempt to open /gnu/store/mx2bgrpxkbdjsmhlxp9a30hbzcilk4cn-binutils-2.32/x86_64-unknown-linux-gnu/lib/libm.a failed
> /gnu/store/8aj9slzwi5vnmi5iszc5jh3hrvndj29c-profile/bin/ld: cannot find -lm
> ...
> --8<---------------cut here---------------end--------------->8---
>
> I believe this is because we have crt1.o, crti.o, and limb.so in the output of
> our glibc package, which clang seems unaware of.
>
> I don't know exactly how to fix this, but I did some digging in the clang
> codebase (cfe-6.0.1 to be exact), and found that the crt1.o, crti.o arguments
> are added in lib/Driver/ToolChains/Gnu.cpp.
>
> These arguments are constructed using something like
> Args.MakeArgString(ToolChain.GetFilePath("crti.o")), which really calls
> Driver::GetFilePath in lib/Driver/Driver.cpp under the hood. Meaning that we
> just need to make Driver::GetFilePath aware of our glibc path and return the
> correct full path to crt1.o and crti.o.
>
> If anyone can help out here it would be much appreciated.
>
> Cheers,
> Carl Dong
> contact@carldong.me
> "I fight for the users"