zig/std/special/bootstrap.zig

// This file is in a package which has the root source file exposed as "@root".
// It is included in the compilation unit when exporting an executable.

const root = @import("@root");
const std = @import("std");
const builtin = @import("builtin");

var argc_ptr: &usize = undefined;

comptime {
    const strong_linkage = builtin.GlobalLinkage.Strong;
    if (builtin.link_libc) {
        @export("main", main, strong_linkage);
    } else if (builtin.os == builtin.Os.windows) {
        @export("WinMainCRTStartup", WinMainCRTStartup, strong_linkage);
    } else {
        @export("_start", _start, strong_linkage);
    }
}

nakedcc fn _start() -> noreturn {
    switch (builtin.arch) {
        builtin.Arch.x86_64 => {
            argc_ptr = asm("lea (%%rsp), %[argc]": [argc] "=r" (-> &usize));
        },
        builtin.Arch.i386 => {
            argc_ptr = asm("lea (%%esp), %[argc]": [argc] "=r" (-> &usize));
        },
        else => @compileError("unsupported arch"),
    }
    // If LLVM inlines stack variables into _start, they will overwrite
    // the command line argument data.
    @noInlineCall(posixCallMainAndExit);
}

extern fn WinMainCRTStartup() -> noreturn {
    @setAlignStack(16);

    root.main() %% std.os.windows.ExitProcess(1);
    std.os.windows.ExitProcess(0);
}

fn posixCallMainAndExit() -> noreturn {
    const argc = *argc_ptr;
    const argv = @ptrCast(&&u8, &argc_ptr[1]);
    const envp = @ptrCast(&?&u8, &argv[argc + 1]);
    callMain(argc, argv, envp) %% std.os.posix.exit(1);
    std.os.posix.exit(0);
}

fn callMain(argc: usize, argv: &&u8, envp: &?&u8) -> %void {
    std.os.ArgIteratorPosix.raw = argv[0..argc];

    var env_count: usize = 0;
    while (envp[env_count] != null) : (env_count += 1) {}
    std.os.posix_environ_raw = @ptrCast(&&u8, envp)[0..env_count];

    return root.main();
}

extern fn main(c_argc: i32, c_argv: &&u8, c_envp: &?&u8) -> i32 {
    callMain(usize(c_argc), c_argv, c_envp) %% return 1;
    return 0;
}