Incorrect MIPS termios constants

Zig Version

0.10.0-dev.4418+99c3578f6

Steps to Reproduce

#12079 apparently exposed an interesting C ABI issue for MIPS Linux that @topolarity found where when trying to run tests like this the output looks malformed like this:

$ cat test0.zig                                                                               
test { }

test "test a" {
    return error.SkipZigTest;
}

test "test b" {
    return error.SkipZigTest;
}
$ ./build/stage3/bin/zig test test0.zig -target mips-linux --test-cmd qemu-mips --test-cmd-bin
Test [2/3] test.test a... SKIP
                              Test [3/3] test.test b... SKIP
                                                            1 passed; 2 skipped; 0 failed.
                                                                                          %    

The issue boils down to this tcsetattr

zig/lib/std/Progress.zig

Line 246 in 5127dae

defer os.tcsetattr(file.handle, .NOW, original_termios) catch {

in getTerminalCursorColumn in std.Progress.

This however is purely a C ABI issue. It should actually work.

Here's reproducible code: it gets termios (the terminal's config) and then sets it. It shouldn't change the terminal at all:

Zig:

const std = @import("std");

pub fn main() !void {
    const current_termios = try std.os.tcgetattr(std.os.STDERR_FILENO);
    try std.os.tcsetattr(std.os.STDERR_FILENO, .NOW, current_termios);
}

zig build-exe x.zig -target mips-linux; qemu-mips x

Outcome: broken terminal with echo etc. not working.

C:

#include <termios.h>
#include <unistd.h>

int main() {
    struct termios current_termios;
    tcgetattr(STDERR_FILENO, &current_termios);
    tcsetattr(STDERR_FILENO, TCSANOW, &current_termios);
}

mips-linux-gnu-gcc -static x.c; qemu-mips a.out

Outcome: terminal is the same as before.

You might need the packages gcc-mips-linux-gnu, qemu-user, and qemu-system-mips for your system in order to reproduce this issue.

Expected Behavior

The terminal doesn't break.

[topolarity]

Oh I thought this was probably a C ABI issue, but it looks like a broken syscall. The layout of termios matches just fine on MIPS and the example works with -lc, so the problem is when Zig performs the ioctl syscall directly

That or there's some kind of initialization dance that libc is doing which Zig is not

[topolarity]

Aha! This is suspicious:

pub const T = struct {
    pub const CGETS = if (is_mips) 0x540D else 0x5401;
    pub const CSETS = 0x5402;
    pub const CSETSW = 0x5403;
    pub const CSETSF = 0x5404;
    pub const CGETA = 0x5405;
    pub const CSETA = 0x5406;
    ....

Indeed almost all of these are incorrect for MIPS, except for CGETS

[Hejsil]

Ops, missclick. Sorry about that

[The-King-of-Toasters]

See arch/mips/include/uapi/asm/ioctls.h for the full list. Also note the comment in include/uapi/asm-generic/ioctls.h:

The architectures that use different values here typically try to be compatible with some Unix variants for the same architecture.

In this case I bet it's copying IRIX.

[marler8997]

This PR is related: #12771

It tries to define the constants the same way the kernel does, however, I haven't confirmed if all ioctl numbers behave this way, there could be some older values that don't use this new mechanism.