crash with x86_64 hello world with assembly

[andrewrk]

This example from the language reference is crashing stage2:

stage3/bin/zig build-exe test.zig
thread 1564356 panic: reached unreachable code
???:?:?: 0x6a455c3 in ??? (???)
???:?:?: 0x7220050 in ??? (???)
???:?:?: 0x73cc5d9 in ??? (???)
???:?:?: 0x71931ab in ??? (???)
???:?:?: 0x701c448 in ??? (???)
???:?:?: 0x701acfb in ??? (???)
???:?:?: 0x73cbef9 in ??? (???)
???:?:?: 0x71e1218 in ??? (???)
???:?:?: 0x70228a6 in ??? (???)
???:?:?: 0x701acfb in ??? (???)
???:?:?: 0x6ed3c77 in ??? (???)
???:?:?: 0x6d50795 in ??? (???)
???:?:?: 0x6d4effd in ??? (???)
???:?:?: 0x6c86e2a in ??? (???)
???:?:?: 0x6c83fa1 in ??? (???)
???:?:?: 0x6ca9329 in ??? (???)
???:?:?: 0x6aacd79 in ??? (???)
???:?:?: 0x6a4463d in ??? (???)
???:?:?: 0x6a43eb7 in ??? (???)
Aborted (core dumped)

pub fn main() noreturn {
    const msg = "hello world\n";
    _ = syscall3(SYS_write, STDOUT_FILENO, @ptrToInt(msg), msg.len);
    _ = syscall1(SYS_exit, 0);
    unreachable;
}

pub const SYS_write = 1;
pub const SYS_exit = 60;

pub const STDOUT_FILENO = 1;

pub fn syscall1(number: usize, arg1: usize) usize {
    return asm volatile ("syscall"
        : [ret] "={rax}" (-> usize),
        : [number] "{rax}" (number),
          [arg1] "{rdi}" (arg1),
        : "rcx", "r11"
    );
}

pub fn syscall3(number: usize, arg1: usize, arg2: usize, arg3: usize) usize {
    return asm volatile ("syscall"
        : [ret] "={rax}" (-> usize),
        : [number] "{rax}" (number),
          [arg1] "{rdi}" (arg1),
          [arg2] "{rsi}" (arg2),
          [arg3] "{rdx}" (arg3),
        : "rcx", "r11"
    );
}

Bonus points if you fix the missing stage3 stack traces before fixing the underlying issue.

[davidgm94]

This hello world is no longer crashing

[davidgm94]

How can I make this into a regression test? Where should I put it?