[LLVMdev] Using JIT code to code a program to call C++

[Óscar Fuentes]

"Paul J. Lucas" <paul at lucasmail.org> writes:

[snip]

> I'm aware that LLVM doesn't know anything about C++ and that one way
> to call C++ functions is to wrap them in C thunks:

Yes, this is the only sane way unless you are willing to replicate the
ABI of your chosen C++ implementation onto your system. Let's forget
about dealing with more than one C++ ABI ;-)

[snip]

> I would think that, because it's a StructType, the alignment would be
> correct and the sizeof(item) would get the size right.  Will that
> work?

Yes. I do the same on my compiler. Please note that this trick is only
necessary if you pretend to put C++ objects on your stack. If all C++
objects your JITted code creates are on the heap, you can simply use
`new' instead of placement `new' in the C function that creates the C++
object and deal with the returned pointer..

> Is there a better way?

It all depends on the charateristics of your language.

[snip]

> but verifyModule() still complains at me because, apparently, there's
> no automatic casting to void* types in LLVM.  How can I solve this
> problem?

You must do the cast yourself, or simply use void* for all pointers for
all your C++ objects and deal with its real type on the upper part of
the compiler.

As said above, it all depends on the details of your language.