GCC cross-compilation from M1 to Intel for macOS

[kornelski]

On x86-64 I've used to use Homebrew's gcc-11 to build x86-64 executables with OpenMP support. Now I've switched to an M1 Mac, but I still need to build x86-64 C executables with OpenMP support. How can I do that? Is it even possible?

Homebrew docs say for cross-compilation there's x86_64-elf-gcc formula, but that's a weird compiler. It's totally not a cross-compiler equivalent of brew's normal gcc. It doesn't seem to support anything. Not just OpenMP is broken:

x86_64-elf-gcc -fopenmp
x86_64-elf-gcc: error: unrecognized command-line option '-pthread'

but I can't even compile a "hello world":

/opt/homebrew/opt/x86_64-elf-binutils/bin/x86_64-elf-ld: cannot find crt0.o: No such file or directory
/opt/homebrew/opt/x86_64-elf-binutils/bin/x86_64-elf-ld: cannot find -lc

and the "elf" part of the name makes me suspect it's not even for macOS mach-O executables. It doesn't support -arch flag either.

• Is the x86_64-elf-gcc usable for building x86-64 macOS executables?
• Do I need to install extra libs/headers/SDK/some wrapper for it to behave like a normal gcc compiler?
• If it's not suitable for cross-compiling to Intel macOS, what's the recommended way? For example, should I install another copy of Homewbrew for Intel, running under Rosetta?

[carlocab]

x86_64-elf-gcc compiles ELF executables. macOS uses Mach-O, not ELF.

If you need to compile for Intel on M1, use Clang. If you need to use GCC specifically, you might be able to build your own cross-compiler, but that's not something Homebrew provides.

Using a Rosetta installation of Homebrew to install an Intel GCC will probably work too.