kill error checking does not work

[psznm]

Zig Version

0.16.0-dev.1424+d3e20e71b

Steps to Reproduce and Observed Behavior

Kill is not returning errors.

I have been trying to reimplement kill because of #26011 and debugging why it is not working as before.

fn kill(pid: std.c.pid_t, sig: u8) std.posix.KillError!void {
    const rc = std.os.linux.syscall2(.kill, @as(usize, @bitCast(@as(isize, pid))), sig);
    // const as_isize: isize = @bitCast(rc);
    // std.debug.print("rc={d}, as_isize={d}\n", .{ rc, as_isize });
    switch (std.posix.errno(rc)) {
        .SUCCESS => return,
        .INVAL => unreachable, // invalid signal
        .PERM => return error.PermissionDenied,
        .SRCH => return error.ProcessNotFound,
        else => |err| return std.posix.unexpectedErrno(err),
    }
}

With this function, which is remiplementation of the kill without some indirection and SIG enum, it never returns me error when I call kill(9999999, 0), the commented out comment prints out "rc=18446744073709551613, as_isize=-3". The value is -3, but std.posix errno checks for -1

Expected Behavior

Kill should return error on error.

[psznm]

Note: I tracked it that it is due to errno changing since 0.15.2. This is reimplementation that works for me:

    fn kill(pid: std.os.linux.pid_t, sig: u8) std.posix.KillError!void {
        switch (errno(std.os.linux.syscall2(.kill, @as(usize, @bitCast(@as(isize, pid))), sig))) {
            .SUCCESS => return,
            .INVAL => unreachable, // invalid signal
            .PERM => return error.PermissionDenied,
            .SRCH => return error.ProcessNotFound,
            else => |err| return std.posix.unexpectedErrno(err),
        }
    }
    fn errno(rc: anytype) std.posix.E {
        const signed: isize = @bitCast(rc);
        const int = if (signed > -4096 and signed < 0) -signed else 0;
        return @enumFromInt(int);
    }

[psznm]

I think this may have either been fixed recently in 6b4f45f, or I may have made a mistake in the reimplementation. Anyway, on current master it works as proven in #26012