Issue with dynamic linking

[Mehdi Sabwat]

Hi,

I am trying to understand the expected behavior of Emscripten when we have a SIDE_MODULE that links to a standard library.

I am having this message:

Assertion failed: missing linked function `_emscripten_log`. perhaps a side module was not linked in? if this global was expected to arrive from a system library, try to build the MAIN_MODULE with EMCC_FORCE_STDLIBS=1 in the environment

with the following code :

test1.c:
#include <dlfcn.h>
#include <stdio.h>
#include <pthread.h>
#include <emscripten.h>

int main(int ac, char **av)
{
  void *handle = dlopen("./libwasmdog.wasm", RTLD_LAZY);
  void (*fun_print_name)(const char *) = dlsym(handle, "print_name");
  fun_print_name(av[1]);
  /*                                                                                                                  
    emscripten_log(EM_LOG_CONSOLE, "removing this call will brake linking\n");                                        
    emscripten_debugger();                                                                                            
  */
  return 0;
}

EMCC_FORCE_STDLIBS=1 emcc -g -s MAIN_MODULE=1 test1.c -o test.html --preload-file ./libwasmdog.wasm -s ALLOW_MEMORY_GROWTH=1

and

dog.c:
#include "animal.h"
#include <stdio.h>
#include <stdlib.h>
#include <emscripten.h>

void print_name(const char *type)
{
  emscripten_log(EM_LOG_JS_STACK, "\n");
  emscripten_debugger();
  printf("Je suis un %s\n", type);
}
emcc -g -s SIDE_MODULE=1 dog.c -o libwasmdog.wasm -s "EXPORTED_FUNCTIONS=['_emscripten_log', '_emscripten_debugger']"

Is this a bug, or am I doing it wrong?

Thank you!

[Sam Clegg]

One this that looks wrong here is that you should be exporting  `print_name` from the side module..  Those emscripten functions are being imported (in this case from JS).

However that doesn't explain why _emscripten_log would be undefined.   One thing you could try is calling `emscripten_log` from the main module too.. that would force the JS code for this function to be included.   If that fixes the problem then I guess you need to `EXTRA_EXPORTED_RUNTIME_METHODS`.  TBH I'm surprised this isn't already included when building with MAIN_MODULE.   I seems like all JS functions should be included in that case, but I must be mis-remembering.

Thank you!

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[Alon Zakai]

I think the emscripten_log issue is

https://github.com/emscripten-core/emscripten/issues/9793

which I am not sure what to do about. Perhaps at minimum we should make that error message also suggest flipping EXPORT_ALL?

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[Alon Zakai]

Actually I see that is a real difference between the backends, so we should flip that flag on automatically. I will open a PR.

Meanwhile as a workaround, -s EXPORT_ALL (on the main module) should fix things for you, Mehdi.

- Alon

[Mehdi Sabwat]

Thanks Alon!

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