stage1 C ABI compatibility

[andrewrk]

This issue is to track C ABI compatibility support in the stage1 compiler.

Here's what support looks like currently:

• integers, floats, pointers, enums, bools work on every target, as parameters and return values
• x86_64: struct & union parameters & return values larger than 16 bytes
• x86_64: struct & union parameters that have at least 1 integer in them
• x86_64: struct & union parameters <= 16 bytes which break structs into parameters
• x86_64: struct & union parameters <= 16 bytes which are all floats
• x86_64: struct & union return values <= 16 bytes
• ARM: struct & union return values
• ARM: struct & union parameters
• C ABI for parameters that is unsupported gives a compile error linking to this issue
• C ABI for return values that is unsupported gives a compile error linking to this issue
• other architectures structs & unions parameters & return values

For those who find this issue from the compile error, leave a comment detailing your specific needs and I'll see if I can code those up for you to unblock you, so you don't have to wait for this issue to be 100% solved.

[andrewrk]

Update:

I just merged a branch into master which does the following things:

• Unsupported C ABI gives a compile error, like this:

const ASmallUnion = extern union {
    r: u8,
};
extern fn foo(x: ASmallUnion) void;

pub fn main() void {
    const x = ASmallUnion{ .r = 0x12 };

    foo(col);
}

/home/andy/downloads/zig/build/test.zig:4:8: error: TODO: support C ABI for more targets. https://github.com/ziglang/zig/issues/1481
extern fn foo(x: ASmallUnion) void;
       ^
/home/andy/downloads/zig/build/test.zig:4:8: note: pointers, integers, floats, bools, and enums work on all targets
extern fn foo(x: ASmallUnion) void;
       ^

• There is a new type of test, C ABI tests, which covers the C ABI that we do suport. See test/stage1/c_abi/* for the source.

Test 1/9 C importing Zig ABI Tests...OK
Test 2/9 C ABI integers...OK
Test 3/9 C ABI floats...OK
Test 4/9 C ABI pointer...OK
Test 5/9 C ABI bool...OK
Test 6/9 C ABI array...OK
Test 7/9 C ABI big struct...OK
Test 8/9 C ABI big union...OK
Test 9/9 C ABI small struct of ints...OK

• Added all targets C ABI support for integers, floats, bools, enums, and pointers
• Added x86_64 C ABI support for big structs and unions (which are passed by memory)
• Added x86_64 C ABI support for small structs which contain at least one integer

[andrewrk]

Zig will now either panic or emit a compile error when C ABI compatibility is required that it doesn't support yet. Therefore this issue is now an enhancement in order to provide additional C ABI compatibility and not a bug.

For those who find this issue from the compile error, leave a comment detailing your specific needs and I'll see if I can code those up for you to unblock you, so you don't have to wait for this issue to be 100% solved.

[bheads]

Running into this issue when trying to work with the godot native headers.
"TODO implement C ABI for x86_64 return types. type 'godot_string'"

https://github.com/GodotNativeTools/godot_headers

[DavidYKay]

Running into this when bringing up the BGFX rendering library on 64-bit Linux.

My code calls the following function:

bgfx_create_vertex_buffer()

Error message:

TODO implement C ABI for x86_64 return types. type 'struct_bgfx_vertex_buffer_handle_s'

bgfx_vertex_buffer_handle_s is defined in this header, using a macro.

The macro evaluates to the following struct definition:

typedef struct bgfx_vertex_buffer_handle_s { 
    uint16_t idx; 
} bgfx_vertex_buffer_handle_t

This seems to correspond to "x86_64: struct & union return values <= 16 bytes," above.

Please advise on how to get unblocked. 😃

Thanks much for your hard work!

[zacharycarter]

I'm using BGFX as well - not sure if @DavidYKay 's issue will affect me as well, but it will most likely end up blocking me too.

Trying to use the CSFML Network API -

const std = @import("std");
const defines = @import("defines.zig");
const ZealErrors = @import("error.zig").ZealErrors;
const sfml = @cImport({
    // See https://github.com/zig-lang/zig/issues/515
    @cDefine("_NO_CRT_STDIO_INLINE", "1");
    @cInclude("SFML/Network.h");
});

var listener: ?*sfml.sfTcpListener = undefined;

pub fn init() u8 {
    listener = sfml.sfTcpListener_create();
    if (listener == null) {
        return defines.QUIT_FAILURE;
    }

    var socket_status = sfml.sfTcpListener_listen(listener, 8080, sfml.sfIpAddress_Any);
    
    return defines.QUIT_SUCCESS;
}

I'm using the CSFML library - csfml: stable 2.4 (bottled), HEAD

I installed via homebrew on macOS High Sierra 10.13.6 (17G65)

Here is the related header file(s) - https://github.com/SFML/CSFML/blob/master/include/SFML/Network/TcpListener.h

Here's the offending function signature written in Zig - pub extern fn sfTcpListener_listen(listener: ?*sfTcpListener, port: c_ushort, address: sfIpAddress) sfSocketStatus;

And the error -

/Users/zachcarter/projects/zeal_zig/src/console_server.zig:23:5: error: TODO: support C ABI for more targets. https://github.com/ziglang/zig/issues/1481
pub extern fn sfTcpListener_listen(listener: ?*sfTcpListener, port: c_ushort, address: sfIpAddress) sfSocketStatus;
    ^
/Users/zachcarter/projects/zeal_zig/src/console_server.zig:23:5: note: pointers, integers, floats, bools, and enums work on all targets
pub extern fn sfTcpListener_listen(listener: ?*sfTcpListener, port: c_ushort, address: sfIpAddress) sfSocketStatus;

And here's the above example, without using @cimport -

const std = @import("std");
const defines = @import("defines.zig");
const ZealErrors = @import("error.zig").ZealErrors;

pub const struct_sfTcpListener = @OpaqueType();
pub const sfTcpListener = struct_sfTcpListener;

pub const sfIpAddress = extern struct {
    address: [16]u8,
};

pub const sfSocketStatus = extern enum {
    sfSocketDone = 0,
    sfSocketNotReady = 1,
    sfSocketPartial = 2,
    sfSocketDisconnected = 3,
    sfSocketError = 4,
};

pub extern const sfIpAddress_Any: sfIpAddress;

pub extern fn sfTcpListener_create() ?*sfTcpListener;
pub extern fn sfTcpListener_listen(listener: ?*sfTcpListener, port: c_ushort, address: sfIpAddress) sfSocketStatus;

var listener: ?*sfTcpListener = undefined;

pub fn init() u8 {
    listener = sfTcpListener_create();
    if (listener == null) {
        return defines.QUIT_FAILURE;
    }

    var socket_status = sfTcpListener_listen(listener, 8080, sfIpAddress_Any);
    
    return defines.QUIT_SUCCESS;
}

[nebulaeonline]

Trying to run @sizeof builtin on packed structs from 2 bytes to 8 bytes, compiler emits the following: error: TODO: support C ABI for more targets. #1481

This is the relevant code (from x86_64.zig):

// Segment Selector
pub const SegmentSelector = packed struct {
    rpl: u2,
    ti: u1,
    index: u13,
};

From kzig.zig:

const m1 = "sizeof(SegmentSelector) == %lu\n";
efi_result = klib.uefi.AsciiPrint(&m1, @sizeOf(x86.SegmentSelector));

[ThatsNoMoon]

I'm trying to use XCB, translating this hello world program into Zig.

Here's what I have so far:

const std = @import("std");
const xcb = @cImport({
    @cInclude("xcb/xcb.h");
});

pub fn main() error!void {
    std.debug.warn("Starting...\n");
    const connection = xcb.xcb_connect(null, null);
    defer xcb.xcb_disconnect(connection);

    const screen = xcb
        .xcb_setup_roots_iterator(xcb.xcb_get_setup(connection)).data;

    const window = xcb.xcb_generate_id(connection);

    xcb.xcb_create_window(connection,
                          xcb.XCB_COPY_FROM_PARENT,
                          window,
                          screen.root,
                          0, 0,
                          150, 150,
                          10,
                          xcb.XCB_WINDOW_CLASS_INPUT_OUTPUT,
                          screen.root_visual,
                          0, null);

    xcb.xcb_map_window(connection, window);

    xcb.xcb_flush(connection);

    const stdin = try std.io.getStdIn();
    stdin.readByte();
}

And the error message:

TODO implement C ABI for x86_64 return types. type 'struct_xcb_screen_iterator_t'

Referring to the type of screen.

Also, I am a newcomer to Zig, so it's possible I'm doing something wrong.

Thank you for your time!

[xxxbxxx]

trying to use https://github.com/cimgui/cimgui
many functions take a struct parameter:

struct ImVec2
{
    float x, y;
};

[shawnl]

Vector ABI depends on the compiler flags on x86_64, and current the c_abi tests have the compiler flags mixed up so that the zig version expects arguments to be passed in registers (such as %ymm0 and %zmm0 that don't exist on earlier CPUs, which only have %xmm0 et cetera) and the c version expects things to be passed on the stack.

But clearly the C can also pass on the stack with certain arguments https://godbolt.org/z/RCPb2c , we are passing -march=native so I don't know what we get the stack behavior https://godbolt.org/z/DzE_Px

[IgorKorobeynikov]

when will these goals be achieved?

[nektro]

when stage2/0.10.0 is released

[a99984b1799]

Getting this using zig-imgui (project code here):

./src/positions.zig:89:39: error: TODO: support C ABI for more targets. https://github.com/ziglang/zig/issues/1481
            _ = ig.Text("%s", position.ticker);
                                      ^

Where:

pub const Holding = struct {
    name: []const u8,
    ticker: []const u8,
[...]

Builds on Windows but not on Linux, both running Zig 0.10.0-dev.3559+d2342370f.

Edit Working around this circumstance with position.ticker.ptr :)

[Vexu]

No longer relevant, test coverage in zig build test-c-abi.

[esnunes]

No longer relevant, test coverage in zig build test-c-abi.

Hey @Vexu , I didn't get why you've closed this issue, is the stage1 fully compatible now? I'm especially interested in the ARM: struct & union parameters issue.

[Vexu]

Stage1 no longer exists.

[IgorKorobeynikov]

😳

[IgorKorobeynikov]

@andrewrk ARM: struct & union parameters fixed now? In stage2 compiller?

[Vexu]

All but complex number tests are passing for arm, if you find some case that doesn't work report it as a new bug.

[IgorKorobeynikov]

Ok

[esnunes]

All but complex number tests are passing for arm, if you find some case that doesn't work report it as a new bug.

You are talking about the master version, right? Thanks

[Vexu]

Most of the ABI improvements should have already landed in 0.10.0 (for self-hosted).

[rofrol]

What about tasks?

• x86_64: struct & union return values <= 16 bytes
• ARM: struct & union parameters
• other architectures structs & unions parameters & return values

They are unchecked in @andrewrk's post.