[LLVMdev] LLVM memory management (original) (raw)

Tim Northover t.p.northover at gmail.com
Sun Mar 23 00:59:38 PDT 2014

Hi Taylor,

1. How does the lli keep itself from being overwritten by a misbehaving program?

It doesn't. If you want that kind of safety you have to generate input IR that checks all its accesses and avoids unsafe constructs.

3. does it support multithreading?

It should be compatible with multithreading. Using current MCJIT, all compilation happens before execution so you can just write IR that uses your OS primitives to create and manage your threads. But doing that management is your responsibility.

(The old JIT and interpreter seem to have some kind of support for a "llvm_start_multithreaded" function to stop LLVM stomping on its own structures during execution, but both of those have issues of their own: you should be using the MCJIT unless you have good reason not to. If you do have good reason, we'd like to hear about it so we can improve MCJIT).

4. does lli allow for multitasking or do you just ran one VM per program?

5. if it does support multitasking how does it keep processes from colliding? 6. if it does not support multitasking and runs one VM per process then what means are there for communication of processes?

There's no LLVM help for running multiple tasks, you have to rely on your OS support again.

7. does lli support emulated virtual memory?

I'm not exactly sure what you mean, but I suspect the answer is "no, do it in your IR using OS primitives".

As Dmitri said, LLVM isn't really designed to be a friendly hosted environment, but a way to compile (and possibly run in the same process) native code.

Cheers.

Tim.

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