Fail to parse glibc math headers when building Python C extensions

[arrufat]

Hi! I am currently developing Python bindings for my image processing library, zignal: https://github.com/bfactory-ai/zignal

Everything was working fine until llvm was replaced by arocc.
Building Python C extensions with @cImport fails because arocc cannot parse glibc's bits/mathcalls.h. The issue occurs when Python.h transitively includes <math.h>, which uses complex macro patterns.

In zignal, just typing zig build python-bindings triggers the bug, but I've prepared a minimal reproduction below with detailed steps and outputs.

Environment:

• Zig version: 0.16.0-dev.457+f90510b08
• OS: Arch Linux (kernel 6.16.8)
• glibc: 2.42
• Python: 3.13

Minimal Reproduction:

main.zig:

const std = @import("std");

const c = @cImport({
    @cDefine("PY_SSIZE_T_CLEAN", {});
    @cInclude("Python.h");
});

pub fn main() void {
    const version = c.Py_GetVersion();
    std.debug.print("Python version: {*}\n", .{version});
}

build.zig:

const std = @import("std");

pub fn build(b: *std.Build) void {
const target = b.standardTargetOptions(.{});
const optimize = b.standardOptimizeOption(.{});

const lib = b.addLibrary(.{
    .name = "test",
    .linkage = .dynamic,
    .root_module = b.createModule(.{
        .root_source_file = b.path("main.zig"),
        .target = target,
        .optimize = optimize,
        }),
    });

    lib.root_module.link_libc = true;
    lib.linkSystemLibrary("python3");
    b.installArtifact(lib);
}

Build command:

zig build

Error output:

error: /usr/include/bits/mathcalls.h:53:1: error: expected ';', found 'an identifier'
__MATHCALL_VEC (acos,, (_Mdouble_ __x));
^
/usr/include/bits/mathcalls-macros.h:22:54: note: expanded from here
__SIMD_DECL (__MATH_PRECNAME (function, suffix)) \
^
[... continues with similar errors for sin, cos, tan, etc.]

Root Cause:

The __MATHCALL_VEC macro in glibc expands through multiple levels:
__MATHCALL_VEC(acos,, (_Mdouble_ __x)) → __SIMD_DECL(__MATH_PRECNAME(acos, )) → __SIMD_DECL(acosf32)

arocc expands __MATH_PRECNAME(acos, ) to acosf32 but then fails to parse the resulting code.

What I've tried:

Preprocessor workarounds don't help (at leats I couldn't make it work):

• @cDefine("__SIMD_DECL(x)", ""): arocc still expands the arguments before discarding
• @cDefine("__MATHCALL_VEC", "__MATHCALL"): arocc has similar issues with __MATHCALL's macro expansion

Let me know if you need anything else.