[LLVMdev] Interactions with threads and native code

[Evan Jones]

I have just begun investigating LLVM because it seems like it might be 
an ideal tool for building tools for playing with software. However, my 
current project is related to parallel programming on shared memory 
multiprocessor systems, so I need thread support. As far as I can tell, 
LLVM currently has no intrinsic support for threads, is this correct? I 
saw the bug that indicates that LLVM's JIT needs some locks to protect 
its data structures, but are there any other issues that might be 
preventing LLVM from executing multithreaded applications?

To help me in my investigations, I wrote a small program that calls the 
Linux clone system call. It turns out that this small test program 
executes correctly with LLVM, which surprised me. Is this just because 
I got lucky, or is this expected behaviour?

Does anyone have any thoughts about if or how LLVM should support 
threads? I was thinking that it might be worthwhile to add a few thread 
primitives to the llvm.* collection of instrinsics. Something like 
llvm.spawn, llvm.join, llvm.lock, llvm.unlock, and llvm.cas would be 
sufficient for my purposes.

Finally, how does LLVM interact with native code? I see in the 
disassembly that it declares the prototype for the clone function, but 
how does it locate the implementation? If it ends up calling "dlopen" 
and "dlsym," how does it know which library to look in? Additionally, 
is it possible to link against arbitrary native code libraries?

Thank you for your assistance,

Evan Jones