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WIP: Add initial syscall/js.copyBytesToJS support #702

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WIP: Add initial syscall/js.copyBytesToJS support #702

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20 changes: 20 additions & 0 deletions targets/wasm_exec.js
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,26 @@
//"syscall/js.valueInstanceOf": (sp) => {
// mem().setUint8(sp + 24, loadValue(sp + 8) instanceof loadValue(sp + 16));
//},

// copyBytesToJS(dst ref, src []byte) (int, bool)
// Originally copied from upstream Go project, then modified:
// https://github.com/golang/go/blob/3f995c3f3b43033013013e6c7ccc93a9b1411ca9/misc/wasm/wasm_exec.js#L404-L416
// param4 and param5 (below) are likely "length" variables of some sort
"syscall/js.copyBytesToJS": (ret_addr, dest_addr, source_addr, param4, param5) => {
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@aykevl aykevl Nov 10, 2019 •
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The calling convention changes have changed this function conceptually to the following:

func copyBytesToJS(returnValue *struct{int; bool}, dst *ref, srcPtr *byte, srcLen, srcCap uintptr)

The following three rules apply to it:

  • large return values are passed as a pointer-to-struct and prepended to the parameter list
  • int64/uint64 (the ref type) are passed as a pointer-to-value
  • slices are split into 3 parts: the pointer to the underlying array, the length, and the capacity.

So yes, param4 is len and param5 is cap.

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@justinclift justinclift Nov 10, 2019

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Thanks. I'll update things accordingly over the next few days. 😄

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@aykevl aykevl Nov 22, 2019

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Any chance you can take a look at this PR? The next release is getting close.

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@justinclift justinclift Nov 22, 2019

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Yep, I can make time this weekend. 😄

let num_bytes_copied_addr = ret_addr;
let returned_status_addr = ret_addr + 4; // address of returned "ok" status variable

const dst = loadValue(dest_addr);
const src = loadSlice(source_addr);
if (!(dst instanceof Uint8Array)) {
mem().setUint8(returned_status_addr, 0); // Return "not ok" status
return;
}
const toCopy = src.subarray(0, dst.length);
dst.set(toCopy);
setInt64(num_bytes_copied_addr, toCopy.length);
mem().setUint8(returned_status_addr, 1); // Return "ok" status
},
}
};
}
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