suppress verbose --target mismatch warning

[mazunki]

nixpkgs/pkgs/build-support/cc-wrapper/add-clang-cc-cflags-before.sh has a flag to suppress the rather annoying (albeit correct) warning:

Warning: supplying the --target x86_64-pc-linux-elf != x86_64-unknown-linux-musl argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead.

This adds an option (enabled by default across the board) to suppress this. Because of how example/ is built, I had to implement it two places (ideally I'd inherit it in example.nix, which is only used as a test currently... maybe we should change that).

[mazunki]

To be clear, I don't think it's correct to ignore the warning, and this is meant as a temporary workaround so that one can actually read the output of the compiler until we have a better solution.

All tests are passing.

[alfreb]

Interesting. Do we know where --target x86_64-pc-linux-elf != x86_64-unknown-linux-musl comes from? I see we're setting ${ARCH}-pc-linux-elf multiple places - should that be x86_64-unknown-linux-musl instead? See e.g. :

cmake/includeos.cmake:set(TRIPLE "${ARCH}-pc-linux-elf")
cmake/library.cmake:set(TRIPLE "${ARCH}-pc-linux-elf")

[mazunki]

I don't know the answer, but some interesting things to look at are:

$ git clone git@github.com:llvm/llvm-project && cd llvm-project
$ grep -rn -- '-elf' include/ lib/
$ grep -rn -- '-elf' test/ unittests/

$ git clone https://git.savannah.gnu.org/git/config.git && cd config
$ grep -rn -- '-elf'

[mazunki]

The warning itself comes from cc-wrapper, which I'm quite confident is calling our patched llvmPackages/clang++. Because clang++ was built for one target, and IncludeOS & unikernels are being built for another, the cc-wrapper freaks out.

I wonder how this behaves on aarch64. Any knowledge on that @elstr-512?

[mazunki]

While looking into some llvmPackages_19 warnings I stumbled across this: llvm/llvm-project#150147 (comment). Could there be a relationship here?

If we need PIE (do we?), -static-pie seems to be preferred for aarch64.

[MagnusS]

For reference, this is where the warning is coming from: https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/cc-wrapper/add-clang-cc-cflags-before.sh#L29

@mazunki this unfortunately has a conflict now after #2316

[mazunki]

Thanks. Do you know if there's a place where I can filter for conflicts on Github so they're quicker to spot, or perhaps subscribe to them?

The conflict actually makes the implementation for this a bit nicer: we won't need a different implementation for the tests.

[mazunki]

Fixed and tested. @MagnusS

[MagnusS]

I think it's fine to suppress this warning for now as we've relied on this functionality for a while. The warning appeared when we upgraded to 25.05. In the longer term we should consider changing the build to avoid this though -- it would be useful with an issue to track this

[mazunki]

Agreed. I can open one.