Standalone programs without main are broken

[kripken]

STR:

#include <emscripten.h>
EMSCRIPTEN_KEEPALIVE void foo() {}

=>

$ ./emcc a.cpp -o a.wasm
error: undefined symbol: main
warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`

@sbc100 Is that related to the recent crt1 changes perhaps?

[sbc100]

Hmm, this seems to be because of the way EXPORTED_FUNCTIONS works. We have the default value in src/settings.js which includes '_main' by default. Then we have the command line -s EXPORTED_FUNCTIONS. I'd forgotten by emscriptens normal behaviour is to only mention undefined symbols that come from the user, not from src/settings.js defaults.

This means that we can't seem a 'main' exists just because 'main' is part of EXPORTED_FUNCTIONS. This means that var HAS_MAIN in jsifier.js isn't occurate and nor is use_start_function in Builder.link_lld.

I suggest that we add a command line flag to signal that a program has no main. We could either use -s EXPORTED_FUNCTIONS=[] or a more explicit flag such as -mno-entry?

If we really want to maintain backwards compat we could also make the reference to main in crt1 a weak ref?