va_arg cannot pass structs of union type or type with bit field correctly

[xxuejie]

Please refer to this gist for the test source code: https://gist.github.com/4063456

This file works correctly when compiling directly using clang:

$ clang va-args-bug.c
$ ./a.out
The original address of a is: 0x12345678
The original type of b is: 9
The current address of a is: 0x12345678
The current type of b is: 9

But if we use emscripten to compile it, the results are not correct:

$ ./emcc va-args-bug.c
$ node a.out.js
The original address of a is: 0x12345678
The original type of b is: 9
The current address of a is: 0x10
The current type of b is: 24

This is very likely to be the reason of Issue #689. But I'm not 100% sure about this.

[kripken]

Thanks for the testcase! Looks like we do not handle byval varargs (a rare combination I am guessing) properly. Patch coming in a bit.

[kripken]

Hopefully this will indeed fix the original issue #689...