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

Tue Aug 25 13:10:22 PDT 2020

Hi Bjoern,

That is really cool :D Is the creation of that table a Windows thingy or is
> this the way the LLVM handles it?

This is a Windows ABI feature, similar to GOTs on MachO and ELF.
RuntimeDyld just needed to be taught to build the table correctly.

Also… since it is COFF related – the never ending story of “finding my
> global constructors” first of all: Yes! I tried using the “initialize”
> function of LLVMJIT – however this only worked when I was loading a Module.
> When I added the object file (from the same source) the constructors were
> not called at all. What also really bothers me, when I load the object from
> disk and iterate over the symbols I will find:
> “_GLOBAL__sub_I_TestModule.cpp” but when I do a lookup on it, the symbol
> will not be found…

This is a known limitation. To enable running static constructors from a
COFF object file we would need a COFF Platform, and a COFF version of
JITLink. The Platform would identify the static constructors when they are
added to the JIT, and the COFF JITLink implementation would make them
accessible despite them being static.

Regards,
Lang.

On Mon, Aug 24, 2020 at 11:07 PM Gaier, Bjoern <Bjoern.Gaier at horiba.com>
wrote:

> Hey Lang,
>
>
>
> That is really cool :D Is the creation of that table a Windows thingy or
> is this the way the LLVM handles it?
>
>
>
> Also… since it is COFF related – the never ending story of “finding my
> global constructors” first of all: Yes! I tried using the “initialize”
> function of LLVMJIT – however this only worked when I was loading a Module.
> When I added the object file (from the same source) the constructors were
> not called at all. What also really bothers me, when I load the object from
> disk and iterate over the symbols I will find:
> “_GLOBAL__sub_I_TestModule.cpp” but when I do a lookup on it, the symbol
> will not be found…
>
> It's like being sooo close to the constructor but den someone takes it
> away from me :< Plus object files seem to be not passed to the
> TransformationFunction so no luck there either. I solved this issue with
> Modules by either using the mentioned function or by changing the
> visibility of the symbol – it seems like both is not possible with an
> object file .w.
>
>
>
> Kind greetings
>
> Björn
>
>
>
> *From:* Lang Hames <lhames at gmail.com>
> *Sent:* 24 August 2020 19:46
> *To:* Gaier, Bjoern <Bjoern.Gaier at horiba.com>
> *Cc:* Stefan Gränitz <stefan.graenitz at gmail.com>; LLVM Developers Mailing
> List <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] ORC JIT - Incorrect support for COFF files?
>
>
>
> Hi Bjoern,
>
>
>
> Using dllimport on my “planschiValue” actually worked! But I have no idea
> why, because the relocation is still a REL32 if I use dumpbin…
>
>
>
> From memory dllimport is like a GOT access: You'll have a REL32 either
> way, but instead of a REL32 directly to the variable you'll end up with a
> REL32 to an entry in a pointer table containing the address of the
> variable, and the code sequence will change to access the variable
> indirectly via the pointer you load.
>
>
>
> -- Lang.
>
>
>
> On Mon, Aug 24, 2020 at 12:57 AM Gaier, Bjoern <Bjoern.Gaier at horiba.com>
> wrote:
>
> Hey Lang and Stefan,
>
>
>
> Using dllimport on my “planschiValue” actually worked! But I have no idea
> why, because the relocation is still a REL32 if I use dumpbin… So how is it
> possible for that to work?
>
> However… when I load an COFF object file, am I able to change the
> relocations to dllimport somehow? I honestly can’t imagine how this would
> work since the machine code is probably already adjusted to use a REL32… or
> something… Just wanted to ask…
>
>
>
> @Stefan Gränitz <stefan.graenitz at gmail.com> I remember your patch! How
> does it deal with extern variables though? As far as I understood from the
> code – not that I understood much – it fixes function calls by having a
> trampoline right?
>
>
>
> Thank you guys!
>
>
>
> Kind greetings
>
> Björn
>
>
>
> *From:* Lang Hames <lhames at gmail.com>
> *Sent:* 22 August 2020 19:50
> *To:* Stefan Gränitz <stefan.graenitz at gmail.com>
> *Cc:* Gaier, Bjoern <Bjoern.Gaier at horiba.com>; LLVM Developers Mailing
> List <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] ORC JIT - Incorrect support for COFF files?
>
>
>
> Hi Stefan, Bjoern,
>
>
>
> For calls across object boundaries __dllimport now supported in
> RuntimeDyld:
> https://github.com/llvm/llvm-project/commit/337e131ca7de48072def7729df69434c37a66eb7
> <https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fgithub.com%2fllvm%2fllvm%2dproject%2fcommit%2f337e131ca7de48072def7729df69434c37a66eb7&umid=9d785513-e9cd-44e5-a111-cb77401a12f6&auth=b6f66d00f8195cc5198eee21f0dbabe6af0a3180-2bd41aad154bd7e67313fcb36c401a0c65d55652>.
> You may just be able to mark your externs as __dllimport for this to work.
> I don't recall whether __dllimport works for data symbols too, but I
> suspect so -- I think it's basically an explicit GOT entry.
>
>
>
> If anyone is ever interested in writing a JITLink COFF implementation I
> will be happy to help out or review patches -- I'd love to get better COFF
> support in tree.
>
>
>
> -- Lang.
>
>
>
>
>
>
>
> On Fri, Aug 21, 2020 at 2:09 PM Stefan Gränitz <stefan.graenitz at gmail.com>
> wrote:
>
> 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
> <https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fgithub.com%2fweliveindetail%2fpj%2dllvm%2fcommit%2f97cd336d458ae9c73232d1b539ceefcdb2f5eb0f&umid=9d785513-e9cd-44e5-a111-cb77401a12f6&auth=b6f66d00f8195cc5198eee21f0dbabe6af0a3180-dffa61903884c3a0176d5f66111470dc6e9b9d2b>
>
> 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>
> <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>
> <llvm-dev at lists.llvm.org>; Lang Hames <lhames at gmail.com>
> <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 “extern int
> planschiValue;” and “void externFunction();”. 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
>
>
>
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> 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
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>
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>
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>
> --
>
> https://flowcrypt.com/pub/stefan.graenitz@gmail.com
>
> 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.
>
> 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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