llvm-ar: Invalid archive when creating thin archives from other archives

[hmartinez82]

Description / Steps to reproduce the issue

Using llvm-ar to create a thin archive from other archives result in invalid files where nm returns empty content and trying to link using the thin archive fails with ld.lld: error: unknown file type

Steps to repro:
dep.c:

int forty_two() {
    return 42;
}

Then running:

cc -c dep.c && \
nm -g dep.o &&  \
ar cr dep.a dep.o &&  \
nm -g dep.a  && \
ar crT archive.a dep.a && \
nm -g archive.a && \
file archive.a

GNU binutils doesn't have this error.

Expected behavior

forty_two
forty_two
forty_two
archive.a: thin archive with 1 symbol entry

Actual behavior

forty_two
forty_two
<nothing is shown here, the output of nm is empty>
archive.a: thin archive with 1684369454 symbol entries

Verification

• I have verified that my MSYS2 is up-to-date before submitting the report (see https://www.msys2.org/docs/updating/)

Windows Version

MINGW64_NT-10.0-26200

MINGW environments affected

• MINGW64
• MINGW32
• UCRT64
• CLANG64
• CLANGARM64

Are you willing to submit a PR?

No response

[hmartinez82]

I found this while building MUMPS in CLANG64. Let me know if I should post this issue in upstream instead.

[lazka]

maybe @mstorsjo knows

[hmartinez82]

This was the workaround: https://github.com/msys2/MINGW-packages/pull/27438/files#diff-bfd25341255b620760277e246efa4c356ed0b5b8803ab6e683a9c8746f5e1825R116

[dragon-archer]

Seemes like an upstream problem. I can reproduce this on Ubuntu.