[LLVMdev] MCJIT finalizeObject output to use in external process

[Dave Pitsbawn]

No, I was asking how to extract the code from MCJIT, and you said it use a
custom memory manager.

When you say that I must treat each section as a block, do you mean that
there is inter-block relative offsets need to be maintained? Or that when I
get a section, I must copy it to target process memory as a one-shot
contiguous block. If it's second, I think we're ok.


On Wed, Mar 25, 2015 at 5:39 PM, Kaylor, Andrew <andrew.kaylor at intel.com>
wrote:

>  Are you asking about the actual mechanism for transferring the bits into
> the remote process or how you locate the generated code in memory?
>
>
>
> The mechanism for transferring the bits is outside the scope of MCJIT.
> The easiest way to locate the generate code is to use a custom memory
> manager as lli does.  MCJIT will call the memory manager to allocate memory
> on a section-by-section basis.  You should treat each section as a
> monolithic block when copying to the remote system because the generated
> code may depend on relative offsets staying fixed.
>
>
>
> -Andy
>
>
>
> *From:* Dave Pitsbawn [mailto:dpitsbawn at gmail.com]
> *Sent:* Wednesday, March 25, 2015 5:00 PM
> *To:* Kaylor, Andrew
> *Cc:* LLVM Developers Mailing List
> *Subject:* Re: [LLVMdev] MCJIT finalizeObject output to use in external
> process
>
>
>
> Aha. Thanks.
>
>
>
> Seems like I need to call mapSectionAddress with the target address. But
> how I copy the code? What function would I call?
>
>
>
> On Wed, Mar 25, 2015 at 4:32 PM, Kaylor, Andrew <andrew.kaylor at intel.com>
> wrote:
>
> Yes, that is one of the intended use models for MCJIT.
>
>
>
> If you look at the source for ‘lli’ you’ll find an option called
> “remote-mcjit” which does exactly this (for testing purposes).
>
>
>
> The key function (which in the lli case is called from lli’s
> RemoteMemoryManager::notifyObjectLoaded method) is
> ExecutionEngine::mapSectionAddress.  This function tells MCJIT to reapply
> relocations to the loaded object as if it were loaded at a different
> address in memory than it actually is.  The client is responsible for the
> particulars of allocating memory in the remote process, determining the
> address of the memory in the remote process’ address space and (after
> calling mapSectionAddress) copying the JIT’d object to the remote process
> memory and setting the memory attributes as needed for execution.
>
>
>
> -Andy
>
>
>
>
>
> *From:* llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] *On
> Behalf Of *Dave Pitsbawn
> *Sent:* Wednesday, March 25, 2015 4:07 PM
> *To:* LLVM Developers Mailing List
> *Subject:* [LLVMdev] MCJIT finalizeObject output to use in external
> process
>
>
>
> A need has arisen to generate code using MCJIT but not in the target
> process instead in a different process (and possibly even different machine
> though not in the scope).
>
>
>
> Reading through the tutorials and MCJIT design document, it seems like
> this is possible or was kept in mind during design of MCJIT.
>
>
>
> How do I achieve this? Are there examples?
>
>
>
> Dave
>
>
>
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