55 lines
1.7 KiB
Zig
55 lines
1.7 KiB
Zig
//! /sbin/init — the first user-space program. Built as its own freestanding
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//! binary (see build.zig), shipped on the boot volume at sbin/init, loaded by
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//! the bootloader, and started in ring 3 by the kernel's user-ELF loader
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//! (src/kernel/usermode.zig). It talks to the kernel only through the
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//! `int $0x80` syscall gate.
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//!
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//! Today it just proves the path — say hello, exit — and grows into the real
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//! init (service supervision) once processes are schedulable (M3).
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const std = @import("std");
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// The M1 syscall numbers (usermode.zig): 0 = exit(code), 2 = write(ptr, len).
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const sys_exit = 0;
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const sys_write = 2;
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fn syscall2(n: u64, a: u64, b: u64) u64 {
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return asm volatile ("int $0x80"
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: [ret] "={rax}" (-> u64),
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: [n] "{rax}" (n),
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[a] "{rdi}" (a),
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[b] "{rsi}" (b),
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: .{ .memory = true });
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}
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fn write(msg: []const u8) void {
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_ = syscall2(sys_write, @intFromPtr(msg.ptr), msg.len);
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}
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fn exit(code: u64) noreturn {
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_ = syscall2(sys_exit, code, 0);
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unreachable; // the kernel never returns from exit
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}
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/// Entry. Naked: the kernel enters with rsp 16-aligned, but a SysV function
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/// expects rsp ≡ 8 (mod 16) on entry (as if reached by `call`) — so re-enter
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/// the ABI with an actual call. The trap after is unreachable.
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pub export fn _start() callconv(.naked) noreturn {
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asm volatile (
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\\call init_main
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\\ud2
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);
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}
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export fn init_main() callconv(.c) noreturn {
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write("init: hello from user space\n");
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exit(0);
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}
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/// No runtime to unwind into — report the panic as a nonzero exit code.
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pub const panic = std.debug.FullPanic(struct {
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fn panic(_: []const u8, _: ?usize) noreturn {
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exit(127);
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}
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}.panic);
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