Improve alternative libc support

[RossComputerGuy]

Right now, I'm looking to develop my own Linux distro using Zig and I have to supply a libc. A libc implementation which I am interested in using is LLVM's libc, I am also interested in using a pure Zig libc but it is harder to detect and supply what the libc. Currently, these are the things I am looking for Zig being able to do:

• Builder API to supply libc library + headers
• Programmatic function / definition detection

[ikskuh]

What about --libc <file> and zig libc?

[RossComputerGuy]

The problem I have is:

1. Scanning which functions are available
2. std.Target detection

[nektro]

1. weak export all of them
2. builtin.target

re 1 if its just a matter of wanting to know which ones to implement first, remove -lc and see which symbols the linker starts complaining about being missing

[kassane]

What about --libc <file> and zig libc?

This reminds me a reference from Andrew.

• https://github.com/ziglang/zig/issues/514#issuecomment-467172534

When it comes to C code, it's common to use -nostdlib and -nostdinc, but in the zig build interface it gets complicated, leaving only the absence of .linkLibC as an alternative solution.

---

I recently tried to port picolibc to zig build. However, so far I have only encountered a link problem.

As is currently the case with emscripten, it would be interesting to add initial support for the rtos and microlibc interfaces, since cross-compilation is also mentioned in microcontrollers.

[RossComputerGuy]

@kassane Was your linker issue related to libc, libm, libutil, etc not being found? I ran into a similar issue when I tried adding my own libc to Zig. The only thing I did was add it into the abi enum and any switches which didn't have an else.

[kassane]

Hi @RossComputerGuy ,

Sorry for the delay in responding.

Yes, I've been having problems with linking, specifically link scripting with lld instead of gnu-ld. Picolibc has a modification to generate a link script for lld (meson), but I need to do more testing on it.

The most critical part of these tests is the toolchain, as compatibility is never 100% (maybe 99.9%) and this where more attention to detail is required, especially for a solo developer.

[RossComputerGuy]

Yes, I've been having problems with linking, specifically link scripting with lld instead of gnu-ld. Picolibc has a modification to generate a link script for lld (meson), but I need to do more testing on it.

Oh, gotcha. Yeah when I tried adding my own libc into my Zig fork, I ran into this linker issue:

error: ld.lld: unable to find library -lm
error: ld.lld: unable to find library -lpthread
error: ld.lld: unable to find library -lc
error: ld.lld: unable to find library -ldl
error: ld.lld: unable to find library -lrt
error: ld.lld: unable to find library -lutil

I got these errors despite targeting glibc, seems like it isn't straight forward to add new libc support into Zig. I'm hoping with this issue that we can get a simpler way to specify custom or unsupported libc without patching Zig.