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Proposed strategy to support WASM in D
6 days ago
AnimusPEXUS
Nov 18
Johan
Nov 19
Pierce Ng
Nov 19
Pierce Ng
November 18
  1. probably two different approaches to supporting wasm is needed simultatiously:
    0.1: [wasm module] + [js glue] -- this is current approach, similar to golang's
    0.2: wasi support - this approach means what wasi platforms provide interface for wasi application to interact with the system

I'm talking here about [wasm module] + [js glue] approach

  1. this approach mean the task have to be separated to two subtasks:
    1.1 js glue code, which allows wasm code to interact with js environment.
    1.2 druntime have to be written, so Dlang code would be compilable with ldc (or yet better with dmd it self) with wasm triplet, without --betterC option, like any usual D program.

not so long ago I've started new project https://github.com/AnimusPEXUS/dwasmjs and I've wrote some basic js code to work with js values from inside D ( https://github.com/AnimusPEXUS/dwasmjs/blob/master/source/dwasmjs/dwasmjsi.js ) it's far from being complete. but the general Idea - is to store js values on js side of js<>d glue code. (also I think reflect module of js could be used to improve js interactions, to avoid eval() function use, as eval would slow everything down)

also, to address memory transfers from js to d (wasm) - I've figured out what js side can ask D side to allocate memory arrays as needed and js should write bytes back to pointer passed by D side.

this js side of glue is working with identifiers (randomly generated unique values). if D side needs to get some string - D side calls function on JS side with id of value from which D side wants to get string, and D side also passes pointer to preallocated array (D side gets size needed for array by calling another function).

in my code I've stacked with need to allocate memory inside of wasm module instance. I've seen ADR's mini-druntime for wasm and seen how he used ldc's special fields to calculate addressing for memory allocation and used special ldc function to grow wasm blob (I think, those function can be called from standard WebAssembly module of JS, avoiding need in special ldc functions)

vvv
so basically, the main problem now in literally is to write WebAssembly version of druntime. gluing it to js is not so problematic.
^^^


as for WASI support, I've didn't read documentation yet, but I imagine it provides some binary interface so it can be used to interact with the system, so WASI, probably should be separate version of druntime - separate from WebAssembly(64)

so currently I'm reading druntime and trying to figureout how to modify it to be compilable in wasm


additionally:

  1. LDC have to support unsigned integers in wasm function parameters, as currently wasm generated by ldc puts i32 type on all parameters.

  2. we have to answer question: does stdc parts of druntime also should be ported to WebAssembly, as I've discovered what, looks like druntime requires struct tm from sys.posix.time module

November 18

also I've collected some useful links for various WASM and JS resources related to WASM<>JS integration for ppl less to Google. here

November 18
On Friday, 18 November 2022 at 00:55:57 UTC, AnimusPEXUS wrote:
> vvv
> so basically, the main problem now in literally is to write WebAssembly version of druntime. gluing it to js is not so problematic.
> ^^^

I took Sebastiaan's thing from two years ago and applied it to new druntime here:

https://github.com/adamdruppe/dmd/tree/wasm


I haven't tried actually compiling it yet though, I've been pretty swamped with work lately. When the new ldc comes out, I'll get Sebastiaan's documentation together and give it a try.

> interact with the system, so WASI, probably should be separate version of druntime - separate from WebAssembly(64)

WebAssembly is a kind of CPU and WASI is a kind of C library.

So it should be two separate versions kinda like how there's version(X86) and version(Windows) and version(CRuntime_Microsoft) all independent (though often used together you don't have to).
November 18

On Friday, 18 November 2022 at 00:55:57 UTC, AnimusPEXUS wrote:

>
  1. LDC have to support unsigned integers in wasm function parameters, as currently wasm generated by ldc puts i32 type on all parameters.

Can you give an example of what goes wrong? i32 is LDC/LLVM's type of signed and unsigned integers, there is no distinction on LLVM IR level.

-Johan

November 18

On Friday, 18 November 2022 at 07:06:08 UTC, Johan wrote:

>

On Friday, 18 November 2022 at 00:55:57 UTC, AnimusPEXUS wrote:

>

Can you give an example of what goes wrong? i32 is LDC/LLVM's type of signed and unsigned integers, there is no distinction on LLVM IR level.

-Johan

for example, if I export function uint fname(uint p1, uint p2), the resulting wasm code treats values as signed. but actually I don't know if it possible for wasm to really know I wast to pass unsigned value.

November 18

On Friday, 18 November 2022 at 07:28:33 UTC, AnimusPEXUS wrote:

>

On Friday, 18 November 2022 at 07:06:08 UTC, Johan wrote:

>

On Friday, 18 November 2022 at 00:55:57 UTC, AnimusPEXUS wrote:

>

Can you give an example of what goes wrong? i32 is LDC/LLVM's type of signed and unsigned integers, there is no distinction on LLVM IR level.

-Johan

for example, if I export function uint fname(uint p1, uint p2), the resulting wasm code treats values as signed. but actually I don't know if it possible for wasm to really know I wast to pass unsigned value.

It looks like that if you look at the number, but in reality WASM makes no distiction, it is up for the application themselves to use the appropriate set of opcodes.

>

The class defines uninterpreted integers, whose signedness interpretation can vary depending on context. In the abstract syntax, they are represented as unsigned values. However, some operations convert them to signed based on a two’s complement interpretation.

https://webassembly.github.io/spec/core/syntax/values.html#integers

https://webassembly.github.io/spec/core/syntax/instructions.html#syntax-sx

November 19

On Friday, 18 November 2022 at 00:55:57 UTC, AnimusPEXUS wrote:

>

0.2: wasi support - this approach means what wasi platforms provide interface for wasi application to interact with the system

WASI is like a libc interface for Wasm and WASI libc is an implementation. A Wasm program calls WASI to access libc/OS-like functionality provided by the Wasm runtime, which could be the web browser or other runtimes.

Earlier this year, for the fantasy game console TIC-80, I implemented the D-Wasm template.

However, I'm stuck actually implementing games in D, (IHIRC) because of a symbol clash between TIC-80's time() API function and WASI libc's time(). For comparison and contrast, with the Zig TIC-80 Wasm interface, Zig source code calls tic.time() for the TIC-80 time() function and thus no symbol conflict.

Here's the code snippet:

// D
void TIC() {
  cls(0);
  for (int x=0; x<240; x+=28) {
    for (int y=0; y<136; y+=28) {
      cx = 12*sinf(time()/30000*(x+y+1)); // <========== time() symbol conflict
      cy = 12*cosf(time()/30000*(x+y+1)); // <========== ditto
      Pir(x, y, 25, 25, x+cx, y+cy);
    }
  }
}

// Zig
export fn TIC() void {
    // some var initialization removed
    tic.cls(3);
    while (ax <= 240) {
      fx = @intToFloat(f32, ax);
      ay = 0;
      while (ay <= 136) {
        fy = @intToFloat(f32, ay);
        ca = 12*std.math.sin(tic.time()/30000*(fx+fy+1)); // tic.time()
        cb = 12*std.math.cos(tic.time()/30000*(fx+fy+1)); // no conflict
        Pir(fx, fy, 25, 25, fx+ca, fy+cb);
        ay += 28;
      }
      ax += 28;
    }
}

Without modifying TIC-80 source code, is there a way to do some 'namespace' thingie for D like how Zig does it?

More generally, as a D newbie, the confusion for me was (still is): Should I be writing D programs (whether for TIC-80 or more mundane platforms like Linux) in D, or in BetterC?

November 19

On Saturday, 19 November 2022 at 01:16:00 UTC, Pierce Ng wrote:

>

Without modifying TIC-80 source code, is there a way to do some 'namespace' thingie for D like how Zig does it?

probably you can try playing with pragma(mangle) for this.

November 19
On Saturday, 19 November 2022 at 01:16:00 UTC, Pierce Ng wrote:
> Without modifying TIC-80 source code, is there a way to do some 'namespace' thingie for D like how Zig does it?

All D symbols are namespaced by their module name. You can expose the JS functions in different modules.

I don't know your specific problem but it ought to just be a case of adjusting the imports on JS and using them through different modules in D.

> More generally, as a D newbie, the confusion for me was (still is): Should I be writing D programs (whether for TIC-80 or more mundane platforms like Linux) in D, or in BetterC?

Always use real D unless it is impractical to do so. No point going through suffering when you don't have to.
November 19

On Saturday, 19 November 2022 at 01:57:21 UTC, Adam D Ruppe wrote:

>

On Saturday, 19 November 2022 at 01:16:00 UTC, Pierce Ng wrote:

>

Without modifying TIC-80 source code, is there a way to do some 'namespace' thingie for D like how Zig does it?

All D symbols are namespaced by their module name. You can expose the JS functions in different modules.

Thanks. I misremembered, the trouble isn't with time() but with trying to use WASI libc's sinf() and cosf(). If I try to use D's std.math instead, the code doesn't compile in BetterC mode:

% make
dub build --quiet --build release --compiler ldc2 --arch wasm32-unknown-unknown-wasm
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4433,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4435,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4437,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4537,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4539,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4541,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4558,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4560,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/math.d(4562,13): Error: undefined identifier `c_long`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(875,5): Error: undefined identifier `fenv_t`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(878,5): Error: undefined identifier `fexcept_t`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(880,5): Error: undefined identifier `fexcept_t`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(888,5): Error: undefined identifier `fenv_t`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(890,5): Error: undefined identifier `fenv_t`
/home/pierce/pkg/ldc/include/d/core/stdc/fenv.d(939,9): Error: undefined identifier `fenv_t`
ldc2 failed with exit code 1.
make: *** [Makefile:7: build] Error 2

In TIC-80's case there is no JS. TIC-80 embeds the wasm3 standalone runtime and makes its (TIC-80's) APIs available to Wasm programs

(Well, TIC-80 also embeds Duktape, thus making it programmable with JS, but that's not relevant here.)

>

Always use real D unless it is impractical to do so. No point going through suffering when you don't have to.

Good point.

Let me update D, TIC-80, etc. and try again.

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