Add support for getentropy in d8

[hoodmane]

Use os.system to read from /dev/urandom and then base 64 encode the result. Then use base64Decode to read the result. Only works when --enable-os-system is passed to d8.

[sbc100]

lgtm, are you using d8 in production somewhere? i.e. what is the motivation for this change?

[hoodmane]

I asked @erikcorry if he could look into ways to improve codegen for Python ceval.c and he said it would be much easier if he could run Pyodide in d8 as opposed to having to build node or such against a branch of v8.

[hoodmane]

But it was surprisingly not too hard to get it to work: https://github.com/pyodide/pyodide/pull/5607/files
This is the only change to Emscripten needed.

[sbc100]

I asked @erikcorry if he could look into ways to improve codegen for Python ceval.c and he said it would be much easier if he could run Pyodide in d8 as opposed to having to build node or such against a branch of v8.

So you are patching / working on v8? Indeed that does sounds like a good use case.

If you just want recent builds of v8 in node you can also use node canary which I think its basically a nightly build: https://nodejs.org/download/v8-canary/

[sbc100]

Looks like you need to add os.system to src/closure-externs/node-externs.js maybe?

[hoodmane]

The same set of tests failed twice in CI but they pass for me locally.

[sbc100]

The closure compilr failure looks real:

building:ERROR: Closure compiler run failed:

building:ERROR: /tmp/emtest_qmeo9dvm/emscripten_temp_3t3ik5j9/hello_world.js:1078:15: ERROR - [JSC_UNDEFINED_VARIABLE] variable os is undeclared
  1078|           if (!os.system) {
                       ^^

1 error(s), 0 warning(s)

emcc: error: closure compiler failed (rc: 1): /root/emsdk/node/20.18.0_64bit/bin/node --max_old_space_size=8192 /root/project/node_modules/.bin/google-closure-compiler --compilation_level ADVANCED_OPTIMIZATIONS --language_in UNSTABLE --language_out NO_TRANSPILE --emit_use_strict=false --externs /root/project/src/closure-externs/closure-externs.js --externs /root/project/src/closure-externs/webgpu-externs.js --externs /root/project/src/closure-externs/v8-externs.js --externs /root/project/src/closure-externs/spidermonkey-externs.js --js /tmp/emtest_qmeo9dvm/emscripten_temp_3t3ik5j9/hello_world.js --js_output_file tmpj2841mhf.cc.js --formatting PRETTY_PRINT
None
None
test_closure_webgpu_wasm64 (test_other.other) ... FAIL

[hoodmane]

Hmm:

ERROR - [JSC_VAR_MULTIPLY_DECLARED_ERROR] Variable os declared more than once. First occurrence: /home/rchatham/Documents/programming/emscripten/third_party/closure-compiler/node-externs/os.js:30:4