-static-libstdc++ unused on macOS

[h-2]

We are building mac binaries with llvm17 installed from homebrew. The built binaries depend on /opt/homebrew/opt/llvm/lib/c++/libc++.1.dylib.
We would like the binaries to not depend on the presence of homebrew, therefore we added -static-libstdc++ to the build, but this is ignored:

clang++: warning: argument unused during compilation: '-static-libstdc++' [-Wunused-command-line-argument]

On Linux this works. What are we doing wrong?

[DimitryAndric]

You are linking libc++, so the option only applies to the GNU specific libstdc++ (which is default on Linux). Unfortunately there seems to be no equivalent -static-libc++ option. You may have to play games with -Wl,-Bstatic, though I am unsure if that will work as expected on macOS. (In general, static linking is discouraged on macOS, it seems.)

[h-2]

You are linking libc++, so the option only applies to the GNU specific libstdc++ (which is default on Linux).

On Linux, -static-libstdc++ -stdlib=libc++ statically links libc++. So at least on Linux, the option refers to whatever c++ standard library is used.

(In general, static linking is discouraged on macOS, it seems.)

Yeah, we don't want to statically link system stuff, but the libc++ is effectively an application dependency when used from homebrew.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Hannes Hauswedell (h-2)

We are building mac binaries with llvm17 installed from homebrew. The built binaries depend on `/opt/homebrew/opt/llvm/lib/c++/libc++.1.dylib`. We would like the binaries to not depend on the presence of homebrew, therefore we added `-static-libstdc++` to the build, but this is ignored: ``` clang++: warning: argument unused during compilation: '-static-libstdc++' [-Wunused-command-line-argument] ```

On Linux this works. What are we doing wrong?

[poyaoc97]

It's orthogonal to the chosen standard library (irrelevant to either libc++ or libstdc++).

The Darwin toolchain doesn't contain the logic found in the GNU counterpart, probably due to the lack of -Bstatic counterpart in ld64:

llvm-project/clang/lib/Driver/ToolChains/Gnu.cpp

Lines 557 to 563 in 5143a12

	bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
	!Args.hasArg(options::OPT_static);
	if (OnlyLibstdcxxStatic)
	CmdArgs.push_back("-Bstatic");
	ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
	if (OnlyLibstdcxxStatic)
	CmdArgs.push_back("-Bdynamic");

Hardcoding it in the linker arguments is likely the way to go for your use case (no -stdlib=libc++ and no change to compiler options):

-nostdlib++ -Wl,/opt/homebrew/opt/llvm/lib/c++/libc++.a,/opt/homebrew/opt/llvm/lib/c++/libc++abi.a

Alternatively, you can download and build libc++ as a dependency like so: https://github.com/poyaoc97/cxxlab/blob/main/cmake/FetchLibcxx.cmake.