glfw: Illegal instruction in pollEvents()

[alichraghi]

Code

const std = @import("std");
const glfw = @import("glfw");
const mem = std.mem;

fn printKey(window: glfw.Window, key: glfw.Key, scancode: isize, action: glfw.Action, mods: glfw.Mods) void  {
    _ = window;
    _ = scancode;
    _ = action;
    _ = mods;
    std.debug.print("{s}\n", .{key});
}

pub fn main() !void {
    try glfw.init();
    defer glfw.terminate();

    try glfw.Window.hint(glfw.Window.Hint.context_version_major, 4);
    try glfw.Window.hint(glfw.Window.Hint.context_version_minor, 5);
    const window = try glfw.Window.create(640, 480, "Hello, mach-glfw!", null, null);
    defer window.destroy();
    try glfw.makeContextCurrent(window);
    window.setKeyCallback(printKey);

    while (!window.shouldClose()) {
        try window.swapBuffers();
        try glfw.pollEvents();
    }
}

while the above code running, if you press a keyboard key that will crash with this messsage:

Illegal instruction at address 0x26832c
lib/glfw/upstream/glfw/src/x11_window.c:0:0: 0x26832c in _glfwPlatformPollEvents (/home/ali/dev/kizi/lib/glfw/upstream/glfw/src/x11_window.c)
lib/glfw/upstream/glfw/src/window.c:1072:5: 0x274e74 in glfwPollEvents (/home/ali/dev/kizi/lib/glfw/upstream/glfw/src/window.c)
    _glfwPlatformPollEvents();
    ^
/home/ali/dev/kizi/lib/glfw/src/main.zig:189:21: 0x22b4fd in main (kizi)
    c.glfwPollEvents();

[alichraghi]

i think this is because currently mach can't build for wayland

[slimsag]

Hi @alichraghi - thanks for the bug report! A few things:

1. I believe that @silversquirl's patch in glfw: patch more undefined behaviour #72 likely fixes this, please try again and let me know. I do not think it is caused by any mismatch of Wayland vs. X11 support but rather is undefined behavior being caught in the GLFW source code by Zig / UBSan.

2. You can build for Wayland if you like today by changing your build.zig:

-glfw.link(b, exe, .{});
+glfw.link(b, exe, .{.linux_window_manager = .Wayland});

It should "just work", but there may be unknown issues present. I wouldn't advise doing this however as GLFW's Wayland backend is still very immature, in the next version of GLFW there will be support for choosing between X11 and Wayland backends at runtime and so we will begin building for both by default. glfw/glfw#1958

3. If you continue to run into such illegal instruction crashes, you can workaround them by building with -Drelease-fast temporarily as that will have Zig disable UBSan - until we track down the source of the undefined behavior and patch it in GLFW source code.

[alichraghi]

thank you! #72 worked for X11. but adding .linux_window_manager = .Wayland cause build error. i believe that's because:

• typing mistake in build.zig

- .Wayland => "_D_GLFW_WAYLAND",
+ .Wayland => "-D_GLFW_WAYLAND",

mach/glfw/build.zig

Line 126 in 82a9cf6

.Wayland => "_D_GLFW_WAYLAND",

• there's a missing header file in lib/glfw/upstream/glfw/src called wayland-xdg-shell-client-protocol.h.

[slimsag]

Ahh, okay. I will see if I can fix this soon (unless someone wants to try and sends PRs for it!)

You're right about the typo.

For wayland-xdg-shell, we will need to add the right apt packages to the fecth.sh script here so our SDK has the headers/libs so we can cross compile. https://github.com/hexops/sdk-linux-x86_64

[slimsag]

Filed #76 and #77 to track these two issues. I will close this one since the original illegal instruction issue is fixed.