Lack of return causes abort() in Emscripten
I received the following Javascript exception from some code compiled with Emscripten. The code was working correctly as a standalone C++ program. This confused me for a while:
uncaught exception: abort() at jsStackTrace@file:///home/new/gitcode/repeatanalysis/progs/r.js:1049:7 stackTrace@file:///home/new/gitcode/progs/r.js:1066:3 abort@file:///home/new/gitcode/progs/r.js:8368:3 _llvm_trap@file:///home/new/gitcode/progs/r.js:4960:7 __Z15test_badret_auxiii [test_badret_aux(int, int, int)]@file:///home/new/gitcode/repeatanalysis/progs/r.js:8079:2 _test_badret@file:///home/new/gitcode/progs/r.js:8089:2 asm._test_badret@file:///home/new/gitcode/progs/r.js:8148:1 ccallFunc@file:///home/new/gitcode/progs/r.js:534:9 @file:///home/new/gitcode/progs/r.html:15:4
The cause was a non-void function failing to return a value. Here’s the complete example:
#include <iostream>
#include <fstream>
#include <vector>
#include "malloc.h"
using namespace std;
int test_badret_aux(int arg1,int arg2,int arg3) {
// return 0;
}
extern "C" {
int test_badret(char *inputstring);
}
int test_badret(char *inputstring) {
test_badret_aux(1,100,100);
return 0;
}
Compiled with (I tried a bunch of options):
emcc ./r.cpp -o r.js -s EXPORTED_FUNCTIONS="['_test_badret']" -s SAFE_HEAP=1 -g -s ASSERTIONS=1
And driven with the following html:
<!DOCTYPE html>
<html>
<body>
<script src="r.js"></script>
<script>
var mystring = "test";
var strptr = Module._malloc(mystring.length);
Module.writeAsciiToMemory(mystring, strptr);
var ret = Module.ccall('test_badret', // name of C function
'number', // return type
['number'], // argument types
[strptr]); // arguments
</script>
</body>
</html>
If I uncomment the return in the above C program, the code no longer aborts. Understandable perhaps. But seemed unusual to me. This was using Firefox (Iceweasel 31.2.0 on Debian Jessie).
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