Was "Undefined symbol 'errno' when linking with wasi-libc", and in particular see bug #2228297 comment #3.

+++ This bug was initially created as a clone of Bug #2228297 +++

Using the following simple reproducer and linking against the Fedora 38 wasm32-wasi-static libs results in a linker error

$ cat e.c
#include <errno.h>

int main(void)
{
        errno = 0;
        return errno;
}
$ clang --target=wasm32-wasi --sysroot=/usr/wasm32-wasi -o e.wasm e.c
wasm-ld: error: /tmp/e-78d8d7.o: undefined symbol: errno
wasm-ld: error: /tmp/e-78d8d7.o: undefined symbol: errno
clang-16: error: linker command failed with exit code 1 (use -v to see invocation)

However doing the same with the wasi-sysroot v20.0 tarball from https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-20/wasi-sysroot-20.0.tar.gz works fine

$ clang --target=wasm32-wasi --sysroot=/tmp/wasi-sysroot -o e.wasm e.c
$


Reproducible: Always

Steps to Reproduce:
1. Try to compile and link the above program
Actual Results:  
Linker error

wasm-ld: error: /tmp/e-78d8d7.o: undefined symbol: errno
wasm-ld: error: /tmp/e-78d8d7.o: undefined symbol: errno
clang-16: error: linker command failed with exit code 1 (use -v to see invocation)


Expected Results:  
Successful compilation/linking.

--- Additional comment from Andrew Clayton on 2023-08-01 18:37:09 PDT ---

Forgot to add that looking for the errno definition in the libraries (with llvm-nm), from the the wasi-sysroot v20.0 tarball pulled from GitHub we see

errno.o:
00000000 D errno

in libc.a

whereas in the libc.a from the Fedora 38 wasm32-wasi-static package we see

errno.o:
00000000 D __EINVAL
00000004 D __ENOMEM

and I only see references to 'U errno' and no 'D errno' in any of the packaged libraries/objects.

--- Additional comment from Josh Stone on 2023-08-09 11:05:51 PDT ---

That's curious. In wasm32-wasi-static's libc.a, I see *two* entries that look like:

errno.o:
00000000 D __EINVAL
00000004 D __ENOMEM

Whereas in rust-std-static-wasm32-wasi, which still bundles its own copy, there is one entry like that, and another with "D errno".
(They only other difference in those libc.a symbols is having dlmalloc.o vs. emmalloc.o)

--- Additional comment from Josh Stone on 2023-08-09 11:22:27 PDT ---

There are two separate errno.c sources that create errno.o objects in libc.a:

libc-bottom-half/cloudlibc/src/libc/errno/errno.c (errno)
libc-bottom-half/sources/errno.c (__EINVAL and __ENOMEM)

However, "%global toolchain clang" enables the post-install /usr/lib/rpm/redhat/brp-llvm-compile-lto-elf, which unpacks the archive (ar x), looks for LLVM bitcode to compile in each object, and then re-packs them (ar r). So with two errno.o, the second overwrites the first while unpacking, and then that's also written on top of the first in the archive when repacking.

I think we could undefine %__brp_llvm_compile_lto_elf (or redefine it to %{nil}) to skip that step.

--- Additional comment from Andrew Clayton on 2023-08-11 08:00:22 PDT ---

Sounds good. Happy to test any new builds...

--- Additional comment from Jan Staněk on 2023-08-14 02:26:25 PDT ---

Thanks both of you for the report and the suggested fix, it now works on my machine :) Update should follow shortly.

--- Additional comment from Fedora Update System on 2023-08-14 02:44:06 PDT ---

FEDORA-2023-d36d498dc0 has been submitted as an update to Fedora 40. https://bodhi.fedoraproject.org/updates/FEDORA-2023-d36d498dc0

--- Additional comment from Fedora Update System on 2023-08-14 02:45:37 PDT ---

FEDORA-2023-d36d498dc0 has been pushed to the Fedora 40 stable repository.
If problem still persists, please make note of it in this bug report.

--- Additional comment from Jan Staněk on 2023-08-14 03:08:53 PDT ---

Note: I have trouble building this for F38 ATM, seems something is broken in koji: https://koji.fedoraproject.org/koji/taskinfo?taskID=104820303. The builds will be incoming once that is resolved.

--- Additional comment from Fedora Update System on 2023-08-16 02:51:32 PDT ---

FEDORA-2023-1276d16f5b has been submitted as an update to Fedora 39. https://bodhi.fedoraproject.org/updates/FEDORA-2023-1276d16f5b

--- Additional comment from Fedora Update System on 2023-08-16 02:54:37 PDT ---

FEDORA-2023-1276d16f5b has been pushed to the Fedora 39 stable repository.
If problem still persists, please make note of it in this bug report.