Infinite loop upon exiting a nodejs program

[cpitclaudel]

I don't have a simple repro yet, but I'm seeing the following in the generated javascript code:

  function _exit(status) {
      __exit(status);
    }function __Exit(status) {
      __exit(status);
    }

function __exit($0) {
 $0 = $0 | 0;
 __Exit($0 | 0);
}

This causes an infinite loop when the node.js program completes:

exception thrown: RangeError: Maximum call stack size exceeded,RangeError: Maximum call stack size exceeded
    at __Exit (/test/output.g3.js:4646:21)
    at __exit (/test/output.g3.js:4108667:2)
    at __Exit (/test/output.g3.js:4647:7)
    at __exit (/test/output.g3.js:4108667:2)
    at __Exit (/test/output.g3.js:4647:7)
    at __exit (/test/output.g3.js:4108667:2)
    at __Exit (/test/output.g3.js:4647:7)
    at __exit (/test/output.g3.js:4108667:2)
    at __Exit (/test/output.g3.js:4647:7)
    at __exit (/test/output.g3.js:4108667:2)
/test/output.g3.js:114
      throw ex;
      ^

I compiled with this:

EMCC_JS_OPTIONS=(-s OUTLINING_LIMIT=200000 # Avoid “excessive recursion” errors at parsing in web workers
                 # (But beware: too low values cause stack overflows in the program)
                 -s DISABLE_EXCEPTION_CATCHING=0 # Let CVC4 catch exceptions
                 -s ABORTING_MALLOC=0 -s ALLOW_MEMORY_GROWTH=1 # Allow dynamic memory resizing
                 -s EXPORTED_FUNCTIONS='["_main"]'
                 -s STRICT=1 -s ERROR_ON_UNDEFINED_SYMBOLS=1)

EMCC_JS_LIBLIKE_OPTIONS=(-s INVOKE_RUN=0 # Don't call main automatically
                         -s NO_EXIT_RUNTIME=1
                         -s MODULARIZE=1 -s EXPORT_NAME="'CVC4'"
                         -s 'EXTRA_EXPORTED_RUNTIME_METHODS=["FS"]')

emcc "${EMCC_JS_OPTIONS[@]}" "${EMCC_JS_LIBLIKE_OPTIONS[@]}" -O3 -g3 -l "nodefs.js" "${EMCC_JS_INPUTS[@]}" -o output.g3.js

Any idea ?

[kripken]

The source for _exit is in src/library.js (search for exit:). Perhaps you have a local change? Or perhaps some custom code that modifies the JS output?

[cpitclaudel]

No local change, and no modifications of the JS output, AFAICT. Does it make a difference that it reads __exit, not _exit?

[kripken]

Oh, right. That __exit might be from your code? Then it could explain part of this, but still it's not clear why _exit differs from what is in the js library. Should be easy to figure out with a repro though.

[cpitclaudel]

I'm trying to get one. I misspoke when I stated that it was only node — it also happens on a regular webpage. It started happening when I moved to incoming.

[cpitclaudel]

Would it help if I sent the compiled program?

[cpitclaudel]

Could this be a recent regression?

When I run on tag-1.37.13, the code looks like this:

  Module["_pthread_mutex_unlock"] = _pthread_mutex_unlock;

  
  
  function __exit(status) {
      // void _exit(int status);
      // http://pubs.opengroup.org/onlinepubs/000095399/functions/exit.html
      Module['exit'](status);
    }function _exit(status) {
      __exit(status);
    }function __Exit(status) {
      __exit(status);
    }

Whereas on incoming, I get this:

  Module["_pthread_mutex_unlock"] = _pthread_mutex_unlock;

  
  function _exit(status) {
      __exit(status);
    }function __Exit(status) {
      __exit(status);
    }

[kripken]

If it's a regression, please bisect, the specific commit would be useful information.

[cpitclaudel]

I can try, but each build cycle takes 25 minutes, so it's going to be a fairly painful task.

[kripken]

Well, I'd guess it might be 7a5744d - perhaps just check that commit and the one before it?

Or if a repro is quicker to make, that's better.

[cpitclaudel]

Thanks, that's very helpful :) I'll try to make a repro.

[cpitclaudel]

Alright, here it is:

#include <unistd.h>

int main() {
  _exit(0);
}

$ emcc helloworld.cpp -o helloworld.js; nodejs helloworld.js
exception thrown: RangeError: Maximum call stack size exceeded,RangeError: Maximum call stack size exceeded
    at __Exit (/scratch/emscripten/helloworld.js:1734:21)
    at __exit (/scratch/emscripten/helloworld.js:2355:2)
    at asm.__exit (/scratch/emscripten/helloworld.js:5715:20)
    at __Exit (/scratch/emscripten/helloworld.js:1735:7)
    at __exit (/scratch/emscripten/helloworld.js:2355:2)
    at asm.__exit (/scratch/emscripten/helloworld.js:5715:20)
    at __Exit (/scratch/emscripten/helloworld.js:1735:7)
    at __exit (/scratch/emscripten/helloworld.js:2355:2)
    at asm.__exit (/scratch/emscripten/helloworld.js:5715:20)
    at __Exit (/scratch/emscripten/helloworld.js:1735:7)
/scratch/emscripten/helloworld.js:110
      throw ex;
      ^

It took me a while, because this works fine:

#include <cstdlib>

void _exit(int c) {
  std::exit(c);
}

int main() {
  _exit(0);
}

[cpitclaudel]

And of course, it works if I return to latest:

$ emsdk activate sdk-1.37.9-64bit
…
$ source /build/emsdk-portable/emsdk_env.sh 
…
$ emcc helloworld.cpp -o helloworld.js
…
$ nodejs helloworld.js
$ 

[kripken]

Thanks, looks like it was a bug in our system libs, fix is in #5325 (bug was old, but it just became noticeable recently with that commit mentioned before).

[kripken]

Fixed by that merge.

[cpitclaudel]

Thanks!