[llvm-dev] JIT-Client for Shared Memory

[Gaier, Bjoern via llvm-dev]

Is… Lang now added? I’m not sure about this system…

My problem is that I can not change the size of the shared memory I’m targeting – so I can only allocate it once, but how do I know how much memory I’m going to need, when each sections requests the memory after each other?
To work around this I first allocate the memory locally and count the bytes it needed. After notifyObjectLoaded I can request the shared memory and do the mapping. But this only covers one module. If I have two modules for example, then I will end up having two shared memories, because the second module will go through the same steps as the first one. But I want to have one coherent memory.

Also the applying of the mapping causes a bug with the new LLVM7 – I already filled out a bug report for this. But I have no idea how things will progress from that point… Still I have no idea about the system…

From: David Blaikie <dblaikie at gmail.com>
Sent: Mittwoch, 7. November 2018 17:34
To: Gaier, Bjoern <Bjoern.Gaier at horiba.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] JIT-Client for Shared Memory

Adding Lang here in case he's got some insight.

I take it the system you're targeting doesn't have the memory limitations that some systems have, where once memory is set executable, it can never be written to? & so you'd like to write some code into a page, execute it, write some more code into the same page and have that execute too?

(I don't know teh JIT architecture well enough to know if that's supported, or if I'm accurately understanding your situation, etc)
On Thu, Nov 1, 2018 at 11:49 PM Gaier, Bjoern via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hello everyone,

I want to use the LLVM to write a JIT client, that works with shared memory. Currently I proceed as following:

I wrote an own class that inherits "RTDyldMemoryManager". The functions "allocateCodeSection" and "allocateDataSection" are allocating local non-shared memory. I store there addresses in a std::vector.
When the function "notifyObjectLoaded" is invoked, I allocate the shared memory - I'm getting the size from the local non-shared memory - and apply the address mapping.
When the function "finalizeMemory" is invoked I copy the code from the local non-shared memory to the shared memory but only one time.

So far so good, this works actually good! Yippie x3

BUT... There is one problem. The shared memory can't be dynamical adjusted. So if I add another module to the current module, then I would go through this process again! Not the "finalizeMemory" process though, but I would allocate another shared memory. This is not what I want! Currently I use the linker first, to work around this problem, but this will not help me if I add object files or libraries to the JIT process - or does it?

So is there any way to work around this?

Kind greetings
Björn
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