[LLVMdev] Dynamically loading native code generated from LLVM IR

Kaylor, Andrew andrew.kaylor at intel.com
Fri Oct 12 17:21:22 PDT 2012

I'm not sure I understand your use case, but MCJIT (as opposed to the legacy JIT) does almost exactly what you're asking for.  It generates an in-memory object file image (using addPassesToEmitMC) and then loads and links it for execution.

If there's some particular detail you don't like in the way this is happening, you might be able to generate a file as you have and then use the RuntimeDyld interface to load it.  The llvm-rtdyld tool does something like this.


-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Baris Aktemur
Sent: Thursday, October 11, 2012 11:58 PM
To: llvmdev at cs.uiuc.edu
Subject: [LLVMdev] Dynamically loading native code generated from LLVM IR


I'm building LLVM IR. I'd like to compile this IR to native code (I don't want JIT) and immediately load it to execute. So far, I've the following:

1) I can emit the IR to native assembly/object file doing the same thing llc does (using TargetMachine::addPassesToEmitFile).
2) I can dynamically load a precompiled .so file (using llvm::sys::DynamicLibrary::getPermanentLibrary), get a function pointer from that file, and execute. 

I can't dynamically load the .o file I produce in step 1 because it's a static library. If I could produce a .so file in step 1, my problem would be solved. llc has a "-relocation-model=pic" option, but the file produced with that did not dynamically load. I got lost in clang's options when trying to find where the "-shared" and "-fPIC" options are used.

So, my question is: Which API should I look at to emit dynamically loadable native code from LLVM IR? 

I would also like to emit code to an in-memory stream instead of a file because everything happens at runtime, but that's a secondary concern.

Thanks in advance.

-Baris Aktemur

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