zig cc: unsupported darwin linker args

[opti-mix]

Thanks a lot for adding zig cc and zig c++ functionality. It is really useful.

I tried to use zig c++ instead of the standard LLVM toolchain for one of my projects. I build it on MacOS. In general, it mostly works, but I've discovered the following issues:

1. There is a number of flags passed to the linker using -Wl,my_linker_option. They are important for proper linking of the project. But some of them are not supported yet.

warning: unsupported linker arg: -search_paths_first
warning: unsupported linker arg: -headerpad_max_install_names
warning: unsupported linker arg: -force_load
warning: unsupported linker arg: -force_load

2. If I configure my CMake-based project to use make and then run make, it seems to work fine as long as make is using just a single thread. But if I use e.g. make -j 2 I start seeing some issues:

zig -c test.cpp -std=c++14 -ffast-math -fno-finite-math-only -g -I/path/to/include -emit-llvm -O0 -o test.o
Invalid argument: -c

It seems as if there is a race condition somewhere. As you can seen in zig's command line it misses c++ after zig somehow.

3. If I configure my CMake-based project to use ninja and then run ninja, I see issues with dependency tracking supported by clang. Specifically, there seems to be an issue with handling of -MF flags (see below). Same project can be build just fine if I use the vanilla LLVM toolchain.

zig: error: no such file or directory: 'test.cpp.o.d'

The following command failed when running ninja:
zig clang -c -MD -MV -MF zig-cache/tmp/eamNMvLXEZYC-test.o.d  -MD -MT -MF test.cpp.o.d -o zig-cache/tmp/eamNMvLXEZYC-test.o test.cpp

It would be nice if these issues could be resolved.

Please let me know if I can provide any additional information that would allow to fix these issues.

[opti-mix]

Oh, one more thing I forgot to mention:

4. If I use CXX="zig c++" cmake it runs into some problems for some targets that play with the compiler name. It seems like cmake does not correctly handle the space between zig and c++ in some cases. So, I created a small shell-wrapper called zigc++ which looks like this:

#!/bin/bash
zig c++ $@

If I then use it like CXX="zigc++" cmake, then the issue disappears. So, maybe it is a good idea to provide such wrappers for zig cc and zig c++ as part of Zig pre-built binaries?

[andrewrk]

zig -c test.cpp -std=c++14 -ffast-math -fno-finite-math-only -g -I/path/to/include -emit-llvm -O0 -o test.o
Invalid argument: -c

you're missing c++ here. zig c++ -c ...

edit: oops, I see that you noticed this. can you confirm that it's a problem on zig's end though?

[opti-mix]

edit: oops, I see that you noticed this. can you confirm that it's a problem on zig's end though?

The thing is: if I use a single-threaded make, it does not happen. It seems to happen only with make -j N, where N > 1. Which indicates that command-line options are passed correctly to zig in a single-threaded make.

[andrewrk]

You could verify this with strace -f -e trace=execve make ... and then see what argv is being passed to zig

[opti-mix]

You could verify this with strace -f -e trace=execve make ... and then see what argv is being passed to zig

Seems like it is a make issue, because make dumps a wrong command line in verbose mode. I tried to use the zigc++ wrapper instead of zig c++ and the issue disappears. Seems like the whitespace between zig and c++ is an issue for CMake or make or both of them.

[andrewrk]

(2) is a make issue as noted above
(3) is solved in e4edc6d
(4) there is no plan to do this; I consider that to be out of scope of the project

As for (1) I am repurposing this issue to address it. If you run into any more independent problems, let's handle those in new issues.

[andrewrk]

Alright so the remaining issue has to do with the fact that Zig uses LLD as the linker, and until very recently the mach-o LLD code was unmaintained. It does not support these flags.

However now I expect this new team to quickly bring LLD up to speed for mach-o, and so I expect this issue to be resolved with the release of LLVM 11 (in 6 months).

[opti-mix]

@andrewrk BTW, I was about to download the latest builds from https://ziglang.org/download/#release-master, but it seems to be not updated since yesterday for some reason. Don't know if it is expected or not.

[opti-mix]

Alright so the remaining issue has to do with the fact that Zig uses LLD as the linker, and until very recently the mach-o LLD code was unmaintained. It does not support these flags.

I don't quite understand this comment. Couldn't Zig just pass the provided -Wl,my_linker_option to a linker "as is", without doing anything about these flags?

Or do you say that the error messages I see are from the LLD linker and not from Zig?