[llvm-dev] Moving to ORCv2 - Compiling debuggable code?

[Geoff Levner via llvm-dev]

I too am in the process of porting our ORC code to ORC v2 and LLJIT. The new API allows me to remove much of our own code, which can only be a good thing. I sometimes get crashes, however, when executing my JIT compiled function, so I thought I would use gdb to try to figure out what is going wrong. And I am dismayed to see that there seems to be no way to provide an event listener to register compiled functions with gdb. LLJIT creates an object linking layer with no listeners, and no way to add listeners afterwards that I can see.

Am I missing something? Is there another way to debug JIT compiled code?

Geoff

[David Blaikie via llvm-dev]

+Lang Hames  the author/owner of the ORC JIT - though he's out of teh office at the moment I think, so might not get a reply until the new year I'd expect. Perhaps other folks familiar with it might chime in, though.

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[Praveen Velliengiri via llvm-dev]

Dear Geoff,

As for as ORCv2 is concerned, there is no event listener facility available as of now.

Thanks

[River Riddle via llvm-dev]

If you are creating your own object linking layer via LLJITBuilder, you could add the notification yourself. For RTDyldObjectLinkingLayer, you can use `setNotifyLoaded`. For ObjectLinkingLayer, I think you would need to use a `ObjectLinkingLayer::Plugin`. I was able to hook the existing GDB registration listener this way.

-- River

[Geoff Levner via llvm-dev]

Hmm, the things of which you speak (LLJITBuilder, setNotifyLoaded(),
ObjectLinkingLayer) do not seem to exist in LLVM 8. We may have to
jump directly from LLVM 7 to LLVM 9 then....

Thanks,
Geoff

[Geoff Levner via llvm-dev]

For anyone interested, the reason our JIT compiled code was crashing is that, in LLVM 8, LLJIT::addIRModule() does not record constructors, so global variables were not constructed. (LLLazyJIT does record constructors, but we don't need LLLazyJIT.) The solution was to derive a subclass of LLJIT and provide an addIRModule() method that records constructors and destructors. Perhaps this was fixed in more recent versions of LLVM...

Geoff

[Stefan Gränitz via llvm-dev]

Hi Geoff

There's been an API change from 8 to 9, but it should work with both
versions. LLJIT is only one possible implementation and doesn't provide
all functionality. Make your own. Hope it helps.

Release 8: https://github.com/weliveindetail/JitFromScratch/commit/4e858ef
Release 9: https://github.com/weliveindetail/JitFromScratch/commit/a4b88a0

Best,
Stefan

--
https://flowcrypt.com/pub/stefan....@gmail.com