Import attribute

[Jiboo]

Hello,

As there is a reflection about a dedicated export attribute in #64, I wondered if there would be any interest for an import attribute?

With a string argument, it may allow imports from multiple modules/host-namespaces, lifting the restriction on --allow-undefined-file to import only from "env".
It would make it more convenient for embeders to specify their API, and users to compile against it.

// env.h
__attribute__((wasm_import("env"))) void print_i32(int32_t);
__attribute__((wasm_import("env"))) void print_i64(int64_t);
...

// test.c
#include <env.h>
__attribute__((wasm_export)) void hello() { print_i32(789); }

Thanks,
JB.

[sbc100]

There is work in progress on this already: #55

[xtuc]

FYI I made WebAssembly/binaryen#1500 some time ago

[sbc100]

Yes WebAssembly/binaryen#1500 looks very similar, but for the .s file format rather than the binary.

[Jiboo]

Thanks, although I'm not sure about how to be able to output this attribute (to the .s) from clang?

I stumbled into the "import_module" attribute, but it look like it didn't make it into upstream (can't find "import_module" in tools/clang/include/clang/Basic/Attr.td).

It looks implemented for rust.

[xtuc]

Interesting, I didn't know that PR against LLVM, but I did implement it on my side as well. (Edit: or I don't remember)

First I bypassed LLVM, see https://github.com/xtuc/holyc/blob/master/include/webassembly/esm.h but the plan was to implement some syntax in the frontend.

[Jiboo]

@xtuc oh, didn't though about dumping it using __asm__

I guess I'll close this as some work along this direction (import attribute) already were investigated.

Thanks again,
JB.