Webassembly -尝试编译代码缓冲区并通过C++通过EM_JS执行它
Webassembly -尝试编译代码缓冲区并通过C++通过EM_JS执行它
提问于 2020-03-19 06:27:12
我正在试验webassembly，并且我已经制作了一个玩具模块，它可以用C++暴力强制素数
extern "C" {
bool isPrime(int n) {
for (int i = 2; i <= n; i++) {
if (n % i == 0) return false;
}
return true;
}
int getPrimes() {
int primesFound = 0;
for (int i = 2; i < 4206969; i++) {
if (isPrime(i)) {
primesFound++;
}
}
return primesFound;
}}
在windows中用emcc /O3编译得到以下字节流：
0x0, 0x61, 0x73, 0x6d, 0x1, 0x0, 0x0, 0x0, 0x1, 0x8, 0x2, 0x60,
0x0, 0x0, 0x60, 0x0, 0x1, 0x7f, 0x3, 0x3, 0x2, 0x0, 0x1, 0x5, 0x6, 0x1, 0x1, 0x80, 0x2,
0x80, 0x2, 0x7, 0x1f, 0x3, 0x6, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x2, 0x0, 0x9, 0x67,
0x65, 0x74, 0x50, 0x72, 0x69, 0x6d, 0x65, 0x73, 0x0, 0x1, 0x6, 0x5f, 0x73, 0x74, 0x61,
0x72, 0x74, 0x0, 0x0, 0xa, 0x4e, 0x2, 0x3, 0x0, 0x1, 0xb, 0x48, 0x1, 0x4, 0x7f, 0x41,
0x2, 0x21, 0x0, 0x3, 0x40, 0x41, 0x2, 0x21, 0x1, 0x2, 0x40, 0x3, 0x40, 0x20, 0x0, 0x20,
0x1, 0x70, 0x45, 0xd, 0x1, 0x20, 0x0, 0x20, 0x1, 0x46, 0x21, 0x3, 0x20, 0x1, 0x41, 0x1,
0x6a, 0x21, 0x1, 0x20, 0x3, 0x45, 0xd, 0x0, 0xb, 0x20, 0x2, 0x41, 0x1, 0x6a, 0x21, 0x2,
0xb, 0x20, 0x0, 0x41, 0x1, 0x6a, 0x22, 0x0, 0x41, 0xf9, 0xe2, 0x80, 0x2, 0x47, 0xd, 0x0,
0xb, 0x20, 0x2, 0xb, 0xb, 0xa, 0x1, 0x0, 0x41, 0x80, 0xc, 0xb, 0x3, 0xa0, 0x6, 0x50这对大多数人来说可能是难以理解的，但VSC的WASM to WAT工具表明，这代表了以下WASM：
(module
(type $t0 (func))
(type $t1 (func (result i32)))
(func $_start (type $t0)
nop)
(func $getPrimes (type $t1) (result i32)
(local $l0 i32) (local $l1 i32) (local $l2 i32) (local $l3 i32)
i32.const 2
local.set $l0
loop $L0
i32.const 2
local.set $l1
block $B1
loop $L2
local.get $l0
local.get $l1
i32.rem_u
i32.eqz
br_if $B1
local.get $l0
local.get $l1
i32.eq
local.set $l3
local.get $l1
i32.const 1
i32.add
local.set $l1
local.get $l3
i32.eqz
br_if $L2
end
local.get $l2
i32.const 1
i32.add
local.set $l2
end
local.get $l0
i32.const 1
i32.add
local.tee $l0
i32.const 4206969
i32.ne
br_if $L0
end
local.get $l2)
(memory $memory 256 256)
(export "memory" (memory 0))
(export "getPrimes" (func $getPrimes))
(export "_start" (func $_start))
(data $d0 (i32.const 1536) "\a0\06P"))从另一个程序调用下面的EM_JS，目的是从WASM调用，它告诉javascript引擎编译一些WASM，然后执行它。
EM_JS(int, call_wasmBlock, (const uint8_t* wasmBlock, uint32_t length), {
let wasmBuf = new Uint8Array(Module.HEAPU8.buffer, wasmBlock, length);
WebAssembly.instantiate(wasmBuf)
.then(
obj => console.log(obj.instance.exports.getPrimes())
);
});我得到了这个错误：
Uncaught (in promise) CompileError: WebAssembly.instantiate(): unexpected section <Export> @+158我不完全确定该怎么做，这主要是在试验webassembly的局限性。
回答 1
Stack Overflow用户
发布于 2020-04-27 06:36:45
index.js
'use strict';
import fs from 'fs';
const bin = fs.readFileSync('test.wasm');
// only checks for primes up to 100
const primeAppBin = new Uint8Array([0, 97, 115, 109, 1, 0, 0, 0, 1, 10, 2, 96, 0, 1, 127, 96, 1, 127, 1, 127, 3, 3, 2, 1, 0, 5, 4, 1, 1, 1, 1, 7, 32, 3, 6, 109, 101, 109, 111, 114, 121, 2, 0, 7, 105, 115, 80, 114, 105, 109, 101, 0, 0, 9, 103, 101, 116, 80, 114, 105, 109, 101, 115, 0, 1, 10, 142, 1, 2, 61, 1, 2, 127, 65, 1, 33, 1, 32, 0, 65, 4, 78, 4, 127, 32, 0, 65, 127, 106, 33, 2, 65, 2, 33, 1, 2, 64, 3, 64, 32, 0, 32, 1, 111, 69, 13, 1, 32, 1, 65, 1, 106, 34, 1, 32, 2, 71, 13, 0, 11, 65, 1, 15, 11, 65, 0, 5, 65, 1, 11, 11, 78, 1, 4, 127, 65, 2, 33, 0, 3, 64, 2, 64, 32, 0, 65, 4, 79, 4, 64, 32, 0, 65, 127, 106, 33, 3, 65, 2, 33, 2, 3, 64, 32, 0, 32, 2, 112, 69, 13, 2, 32, 2, 65, 1, 106, 34, 2, 32, 3, 71, 13, 0, 11, 11, 32, 1, 65, 1, 106, 33, 1, 11, 32, 0, 65, 1, 106, 34, 0, 65, 228, 0, 71, 13, 0, 11, 32, 1, 11, 11, 9, 1, 0, 65, 128, 12, 11, 2, 160, 6]);
(async () => {
let buff;
const imports = {
env: {
execWasm: (byteOffset, length) => {
WebAssembly.instantiate(new Uint8Array(buff, byteOffset, length)).then(app => console.log(app.instance.exports.getPrimes() + ' primes found'));
}
}
};
const app = await WebAssembly.instantiate(bin, imports);
const { memory, test } = app.instance.exports;
const view = new Uint8Array(memory.buffer, 0, primeAppBin.length);
for (let i in view) view[i] = primeAppBin[i];
buff = memory.buffer;
test(view.byteOffset, view.byteLength);
})();test.cpp
// emcc -O3 "test.cpp" -o "test.wasm" -s STANDALONE_WASM -s EXPORTED_FUNCTIONS="['_test']" -s ERROR_ON_UNDEFINED_SYMBOLS=0 -Wl,--no-entry -msimd128 -s INITIAL_MEMORY=64kb -s ALLOW_MEMORY_GROWTH=0 -s TOTAL_STACK=0kb
#include <emscripten.h>
extern "C" {
extern void execWasm(int byteOffset, int length);
EMSCRIPTEN_KEEPALIVE
void test (int byteOffset, int length) {
execWasm(byteOffset, length);
}
}primes.cpp
// emcc -O3 "primes.cpp" -o "primes.wasm" -s STANDALONE_WASM -s EXPORTED_FUNCTIONS="['_getPrimes']" -s ERROR_ON_UNDEFINED_SYMBOLS=0 -Wl,--no-entry -msimd128 -s INITIAL_MEMORY=64kb -s ALLOW_MEMORY_GROWTH=0 -s TOTAL_STACK=0kb
extern "C" {
bool isPrime(int n) {
for (int i = 2; i < n - 1; i++) {
if (n % i == 0)
return false;
}
return true;
}
int getPrimes() {
int primesFound = 0;
for (int i = 2; i < 4'206'969; i++) {
if (isPrime(i)) {
primesFound++;
}
}
return primesFound;
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/60748355
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