Weird C interop behavior, when targeting x86_64-windows-gnu

[km19809]

Zig Version

0.9.0

Steps to Reproduce

1. To get codes:

git clone https://github.com/km19809/zig-raylib
git submodule init
git submodule update

2. To run the program:

zig build -Dtarget=x86_64-windows-gnu
zig-out/bin/main.exe

Expected Behavior

In examples/main.zig:52, I got a C struct that represents the current mouse position.
The position's y value should be changed into the correct value, as the mouse moves.

Snippets:

1. examples/main.zig

        const raylib=@cImport({@cInclude("raylib.h");});
        //...
        const mousePosition=raylib.GetMousePosition(); // It returns raylib.Vector2
        circle.position.x=@floatToInt(i32,mousePosition.x);
        circle.position.y=@floatToInt(i32,mousePosition.y);

2. GetMousePosition() from raylib/src/rcore.c:3737

Vector2 GetMousePosition(void)
{
    Vector2 position = { 0 };

#if defined(PLATFORM_ANDROID) || defined(PLATFORM_WEB)
    position = GetTouchPosition(0);
#else
    position.x = (CORE.Input.Mouse.currentPosition.x + CORE.Input.Mouse.offset.x)*CORE.Input.Mouse.scale.x;
    position.y = (CORE.Input.Mouse.currentPosition.y + CORE.Input.Mouse.offset.y)*CORE.Input.Mouse.scale.y;
#endif

    return position;
}

3. The definition of raylib.Vector2 in auto-generated cimport.zig

pub const struct_Vector2 = extern struct {
    x: f32,
    y: f32,
};
pub const Vector2 = struct_Vector2;

Actual Behavior

The value of mousePosition.y is always 0.
This does not happen when the target is native x86_64-linux.
It only happens when the target is x86_64-windows-gnu. I tested this in both Linux (cross-compile) and Windows (native) hosts.
I also tried compiling c code(core_input_mouse.c) that uses GetMousePosition(), then it worked correctly.

I used vsdbg for debugging this, but I cannot find any solution.
All the values from the raylib struct, CORE.Input.Mouse(raylib/src/rcore.c:3745) , were correct.
But when the mouse position struct passed to zig, its y value suddenly became 0.

Is it related to alignment or something?

[rohlem]

I imagine this might be a C ABI *compatibility issue (as in, currently unimplemented / incorrect implementation).
Issue #1481 tracks this for stage1 - the checkmark for "x86_64: struct & union return values <= 16 bytes" is unticked.
You might be able to work around this in the short term by storing the struct somewhere in C code and only passing the pointer over to Zig.

[km19809]

I imagine this might be a C ABI *compatibility issue (as in, currently unimplemented/incorrect implementation). Issue #1481 tracks this for stage1 - the checkmark for "x86_64: struct & union return values <= 16 bytes" is unticked. You might be able to work around this in the short term by storing the struct somewhere in C code and only passing the pointer over to Zig.

I changed the function to the other one that does not return a struct. It worked.
As you said, it was a C ABI problem. It seems duplicated, so I'll close this issue.
Thank you for your comment!