[llvm-dev] Questions about moving from MCJIT to Orc JIT

Thu Jun 27 02:47:38 PDT 2019

Thanks for the input! I was able to write my own Generator function for the JITDylib!
Thank you a lot x3

From: Praveen Velliengiri <praveenvelliengiri at gmail.com>
Sent: Donnerstag, 27. Juni 2019 10:55
To: Gaier, Bjoern <Bjoern.Gaier at horiba.com>
Cc: Lang Hames <lhames at gmail.com>; llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Questions about moving from MCJIT to Orc JIT

Nice!
Let me try to answer some questions,
Before that I have to mention this is ORC version 2 APIs and this is where the project is moving forward.
JITDylib is the symbol table, basically for a JIT Symbol it have an associated materializers, (you can think of it like an entity that generate the address for that symbol),
Example: compiler are materializers.
So to add symbols to your own JIT you can define them in JITDylib.

For example, Suppose you want to add "your host process (on which JIT runs) symbols to the JIT".
You can do
JD.setGenerator(DynamicLibrarySearchGenerator::GetForCurrentProcess(DL.getGlobalPrefix()))

Under hood, ORC normally search for your host symbols in the defGenerator if it can't find symbols anywhere else.
You can look at core.cpp at line 1163 to see how it works!

I highly recommended you to watch "Updating ORC for Concurrency" dev meeting talks, it is explained in detail,,
For question 4, I don't know maybe If I know after sometime I will write here :)

Thanks

On Thu, 27 Jun 2019 at 14:00, Gaier, Bjoern <Bjoern.Gaier at horiba.com<mailto:Bjoern.Gaier at horiba.com>> wrote:
Hey Praveen,

Thanks for your help! I still have questions and try providing some context.

For questions:
2.) I exactly mean that! Sadly I was not able to understand how to use the ‘define’ function, I tried that:
[cid:image001.png at 01D52CDE.1C37ABB0]
I had no idea how to deal with that >o<

2.1.) With MCJIT I was actually used to getting the name of a function and then ‘answering’ with an address. Is that behavior not possible with OrcJIT anymore? I actually tried looking into the ‘setGenerator’ function of the JITDylib. As a test I came up with this:
[cid:image002.png at 01D52CDE.1C37ABB0]
This was pretty cool, because I actually saw the missing function ‘puts’ but I have no idea how to reply with an  address for ‘puts’. Returning ‘Names’ actually makes the application pause and not go on.

4.) I used the code of Kaleidoscope JIT for my little experiments. If I understood it correctly, the JIT process is completed after I used the lookup function to find a symbol in the code. Now I would like to reset the instance of the Kaleidoscope JIT I had, to jit new modules, which are not related to the previous modules I jitted.
Kind greetings
Björn

From: Praveen Velliengiri <praveenvelliengiri at gmail.com<mailto:praveenvelliengiri at gmail.com>>
Sent: Donnerstag, 27. Juni 2019 08:21
To: Gaier, Bjoern <Bjoern.Gaier at horiba.com<mailto:Bjoern.Gaier at horiba.com>>; Lang Hames <lhames at gmail.com<mailto:lhames at gmail.com>>
Cc: llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Subject: Re: [llvm-dev] Questions about moving from MCJIT to Orc JIT

Hi Bjoern,
CC'ing Lang hames

For questions,
1. In short yes, you can replace the memory manager, default one provided is section memory manager.

2. If you mean by " address of already compiled code", yes you can do that.
 Like this
 JITDylib.define(absoluteSymbols, ( Your_own_symbol , JITTargetAddress(Address of function))), now ORC can resolve all the references to Your_own_symbol to the provided the Address.

3. Yes, all the class/function with legacy prefix will be removed in subsequent releases.

4. Could please provide some more context on this? Like it's usage model, what goal you are aiming for?

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