[llvm-dev] ORC JIT - Incorrect support for COFF files?

[Stefan Gränitz via llvm-dev]

Hi Björn

I made a workaround for this specific issue a long time ago for the
Projucer C++ JIT Engine. It basically forwards the call to another stub
that provides enough space to encode a full 64-bit address. The patch is
based on LLVM 3.9, so I guess it won't work out-of-the-box on a recent
release, but it may give you enough hints to figure it out on your own:
https://github.com/weliveindetail/pj-llvm/commit/97cd336d458ae9c73232d1b539ceefcdb2f5eb0f

Alternatively, you could consider a memory manager that makes sure all
calls are within a 32-bit range. For the code you JIT yourself, this
should be no problem. In case you have to link against an old MSVCRT
though, this is not possible, because it has a fixed load address that's
far beyond the 32-bit range from any heap allocation you can make for
your JITed code. That's been our issue back then and so this patch was
the last resort.

Please also note: this is for freestanding function only. I didn't
consider member function calls, etc. (addend is always 0) because it was
not relevant for the specific issue.

Hope it helps
Stefan

On 21/08/2020 13:22, Gaier, Bjoern via llvm-dev wrote:
>
> I figured out that this problem is caused because “planschiValue” has
> a REL32 relocation and the addresses between the code and the variable
> overflows 32bit.
>
> Is there any workaround for this kind of issue?
>
>  
>
> *From:*llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of
> *Gaier, Bjoern via llvm-dev
> *Sent:* 20 August 2020 12:15
> *To:* LLVM Developers Mailing List <llvm-dev at lists.llvm.org>; Lang
> Hames <lhames at gmail.com>
> *Subject:* [llvm-dev] ORC JIT - Incorrect support for COFF files?
>
>  
>
> Hey LLVM-Mailing-List and Lang,
>
>  
>
> I’m still learning how to use the ORC JIT but I finally reached the
> point to JIT and execute some code. For this purpose I created a test
> file (TestModule.cpp) and compiled it with Clang, generating two
> different files, one in the LLVM IR format and one in the Microsoft
> COFF format.
>
>  
>
> The JIT resolves all undefined references, including
> “externintplanschiValue;” and “voidexternFunction();”. Using the IR
> Module I will get the correct address for “planschiValue” and the
> correct value – however this is not the case for the object file.
>
> For the object file I get (via printf from the module) the address
> 0x000002295D6B003C while the actual address is 0x00007FF71D9959A4.
>
>  
>
> I’m really surprised about this, because the IR module works with no
> problem. I attach the source code, the IR file and the resulting
> object file (including its assembly file).
>
>  
>
> Any ideas what I’m doing wrong?
>
>  
>
> Thank you for the help in advance and kind greetings
>
> Björn
>
>  
>
> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
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> Tajika, Ergin Cansiz.
>
> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
> USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr.
> Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Junichi
> Tajika, Ergin Cansiz.
>
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-- 
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