llvm dev - Mar 2015 - [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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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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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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