//! The user-space process entry shim. Every user binary roots `_start` here (via
//! `entry = _start` in build.zig) and forces this file to be analysed with
//! `comptime { _ = &runtime.start._start; }`, so the whole runtime is linked in.

const std = @import("std");
const system = @import("system.zig");

/// The kernel enters at `_start` with rsp 16-aligned, but a SystemV function expects
/// rsp ≡ 8 (mod 16) on entry (as if reached by `call`). The `call` below pushes
/// the 8-byte return address, satisfying the ABI before any Zig frame runs; the
/// `ud2` is a safety net if `rt_start` ever returns.
pub export fn _start() callconv(.naked) noreturn {
    asm volatile (
        \\call rt_start
        \\ud2
    );
}

/// The first Zig frame. The heap is lazy (first alloc grows it), so there is no
/// runtime init to order here — just hand control to the program's `main`.
export fn rt_start() callconv(.c) noreturn {
    const root = @import("root"); // the user binary's root source file
    root.main();
    system.exit(0);
}

/// No runtime to unwind into — report a panic as a nonzero exit code.
pub const panic = std.debug.FullPanic(struct {
    fn panic(_: []const u8, _: ?usize) noreturn {
        system.exit(127);
    }
}.panic);