Windows is trivial to cross compile for because there is a single set of headers. And for DLLs Windows compiler like to generate an import lib. Which is basically a stub function for all exports.

Linux is stupid and sucks. Linux doesn’t have a single set of headers because programmers in the 80s didn’t know better. And Linux linking to a shared library expects you to have a full copy of the library you expect to exist at runtime. Which is fucking stupid and ass backwards. But I digress.

So. Why is Zig awesome for crosscompiling C++? Because Zig fixed Linux sucking ass. Zig moves mountains to generate thin “import libs” of the half dozen .so files you need to link against to run on Linux.

If you want to cross compile C++ for Linux all you need is clang++ executable, headers, and those stub .so files. Zig generates the libs implicitly as part of its zig cc build process. I’m asking for the half dozen (C) or dozen (C++) libs to be explicitly exportable by Zig. So that they can be trivially used in other build systems.

I’ve got a custom polyglot build system that leverages Zig. But I have to zig cc a hello_world.cpp and parse the output to get the paths to those libs. Which is annoying and janky.

Hopefully that helps?

A straightforward implementation of memchr, i.e. finding the index of a particular byte inside an array of bytes, looks like this:

    for (bytes, 0..) |byte, i| {
        if (byte == search) return i;
    }
    return null;

But it's desirable to use tricks to make the function really fast, such as assuming that you can read up to the page boundary with SIMD instructions[1]. This is generally true on real world hardware, but this is incompatible with the pointer provenance memory model, which is load-bearing for important optimizations that C, C++, Rust, and Zig all rely on.

So if you want to do such tricks you have to do it in a black box that is exempt from the memory model rules. The Zig code I link to here is unsound because it does not do this. An optimization pass, whether it be implemented in Zig pipeline or LLVM pipeline, would be able to prove that it writes outside a pointer provenance, mark that particular control flow unreachable, and thereby cause undefined behavior if it happens.

This is not really LLVM's fault. This is a language shortcoming in C, C++, Rust, Zig, and probably many others. It's a fundamental conflict between the utility of pointer provenance rules, and the utility of ignoring that crap and just doing what you know the machine allows you to do.

[1]: https://github.com/ziglang/zig/blob/0.14.1/lib/std/mem.zig#L...