[llvm-dev] RuntimeDyLdCOFF and RTTI on Windows

Mon Oct 24 16:49:09 PDT 2016

I have a similar build tree to what you describe on Windows, but I get this:

$ clang -c -emit-llvm repro_input.cpp -std=c++11 -o t.bc
$ lli t.bc
LLVM ERROR: Program used external function '??_7type_info@@6B@' which could
not be resolved!

It looks like people have already reported similar issues. Have you done
anything to get past this kind of problem?

On Sat, Oct 22, 2016 at 7:18 AM, Stefan Gränitz via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Lang, hi dev-list (as it may be interesting for others too)
>
> With the cpp file attached, the repro is actually as simple as this:
> $ clang -std=c++11 -emit-llvm repro_input.cpp -c -o repro_input.bc
> $ lli repro_input.bc
>
> On Mac this prints:
> dynamic_cast worked! dummy is 1
>
> On Windows this prints:
> dynamic_cast failed
>
> As the issue is reproducible with lli, it's probably unrelated to the COFF
> implementation as originally stated.
> I built LLVM and Clang from release39 HEAD and used both, clang and lli
> from this build. OS versions and CMake flags are:
>
> * OSX 10.10.6 with -DLLVM_ENABLE_RTTI=ON -DLLVM_ENABLE_EH=ON
> -DLLVM_TARGETS_TO_BUILD=X86
> * Windows 10 64bit OS Build 14393.222 with -DLLVM_ENABLE_RTTI=ON
> -DLLVM_ENABLE_EH=ON -DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_USE_CRT_DEBUG=MDd
> -DLLVM_USE_CRT_RELEASE=MD
>
> Hope this helps nailing down the issue. Maybe I can help fixing it, if you
> can provide a few pointers where to start :) If you need any more info
> please let me know.
>
> Cheers
> Stefan
>
> Am 19.10.16 um 12:10 schrieb Stefan Gränitz:
>
> Hi Lang, thanks for getting back to this.
>
> Did you get a chance to run this on a debug build? Did it trigger an
> assertions/unreachables? Or did the cast just fail?
>
> Yes, I use debug builds of Clang and LLVM (both 3.9.1). We have a pretty
> special setup in the Projucer, but with "95% certainty":
> Clang output is correct. Loading the binary objects with RuntimeDyLd
> produces the problem. I spent quite some time debugging this and the fact
> that data is incomplete though it's in the right place feels similar to
> what I experienced with exceptions on Win64 (which turned out to be missing
> registration calls https://llvm.org/bugs/show_bug.cgi?id=24233).
>
> Will you be at the dev meeting? We could take a look at this in one of the
> labs.
>
> Sooner or later I will make it to a Bay Area dev meeting, promise!
> Unfortunately not in November as I will be at ADC in London. However, I
> will try to reproduce the issue in a minimal example during our Berlin
> Hackday on Saturday, that's a good challenge! If successful I will put it
> on GitHub and let you know! Maybe you guys then find a solution or make a
> plan at the dev meeting.
>
> Thanks
> Stefan
>
> Am 18.10.16 um 21:35 schrieb Lang Hames:
>
> Hi Stefan,
>
> Did you get a chance to run this on a debug build? Did it trigger an
> assertions/unreachables? Or did the cast just fail?
>
> Will you be at the dev meeting? We could take a look at this in one of the
> labs.
>
> Cheers,
> Lang.
>
>
> On Tue, Oct 11, 2016 at 1:52 AM, Stefan Gränitz <stefan.graenitz at gmail.com
> > wrote:
>
>> Thanks Lang for forwarding this to the list
>> The symptom in a nutshell: I cannot get dynamic_cast to work in JITed
>> code on Windows
>>
>> Reid, do you have an idea whether: it's a bug / it's just not implemented
>> yet / I am missing something?
>>
>> Just to rule out one other possibility, Reid: does Windows require any
>> special calls to register C++ RTTI?
>>
>>
>> There's some more details in the original mail.
>>
>> Thanks
>> Stefan
>>
>> Am 07.10.16 um 02:29 schrieb Lang Hames via llvm-dev:
>>
>> HI Stefan,
>>
>> CC'ing Reid Kleckner, who might have some insight here, and llvm-dev as
>> this may be of interest to other windows JIT users.
>>
>> I am facing the issue that C++ dynamic_cast doesn't work for types
>>> loaded from object files with RuntimeDyLd.
>>
>>
>> <snip>
>>
>> Do you think it is possible that RuntimeDyLd misses type info data in
>>> the COFF file or doesn't wire it up correctly?
>>> I set ProcessAllSections = true, but I didn't recognize any change. I
>>> found that RuntimeDyLdCOFF does not override finalizeLoad like the ELF
>>> and MachO versions. The function call's comment reads "Give the
>>> subclasses a chance to tie-up any loose ends" -- possibly missing
>>> functionality?
>>>
>>
>> Unfortunately I don't have a windows machine to test on, so it's
>> difficult to know for sure. From a quick look at the IR, it seems like the
>> Window's C++ ABI implementation of dynamic_cast works similarly to
>> Darwin's: The type info pointers for the reference type and cast type are
>> passed in to the function, so as long as memory has been allocated for the
>> type info I would have expected this to "just work". My best guess for why
>> it wouldn't is that RuntimeDyldCOFF is a missing relocation somewhere. What
>> happens when you run this code on a debug build? Do you hit the
>> llvm_unreachable at the bottom of the resolveRelocation switch?
>>
>> Just to rule out one other possibility, Reid: does Windows require any
>> special calls to register C++ RTTI?
>>
>> Finally, regarding the ProcessAllSections flag: it tells RuntimeDyld to
>> call the memory manager interface for every section, not just the sections
>> that RuntimeDyld thinks are necessary for execution. This was a hack to
>> make debug info sections visible to clients who are interested in them. It
>> can be important if your object file contains metadata sections that are
>> required, but not referenced in the file. I don't think it should affect
>> this case though.
>>
>> - Lang.
>>
>>
>> On Thu, Oct 6, 2016 at 4:37 AM, Stefan Gränitz <stefan.granitz at roli.com>
>> wrote:
>>
>>> Hi Lang
>>>
>>> You are not only the maintainer for ORC but also for RuntimeDyLd right?
>>> May I ask if you know about problems reading RTTI data from COFF object
>>> files on Windows?
>>>
>>> I am facing the issue that C++ dynamic_cast doesn't work for types
>>> loaded from object files with RuntimeDyLd. I inspected my object files
>>> compiled with Clang-3.9 (pure, not cl2) and they seem to include all the
>>> necessary info. When I link (with MS link) and run the static build I
>>> get the expected behavior. Correspondingly I'd consider the RTTI
>>> emission in Clang to work correctly.
>>>
>>> When I load the object files with RuntimeDyLd at runtime, I face the
>>> following troubles in vcruntime140.dll:
>>> * invoking dynamic_cast: the RTTI Complete Object Locator queried in
>>> __RTDynamicCast (rtti.cpp) has incomplete data, which tricks the runtime
>>> to always belief the number of base classes is zero, that's why
>>> dynamic_cast never succeeds
>>> * invoking typeid(variable).name(): the runtime's __std_type_info_name
>>> (std_type_info.cpp) receives a corrupt type data pointer, which causes
>>> an access violation when reading from one of its members
>>>
>>> Do you think it is possible that RuntimeDyLd misses type info data in
>>> the COFF file or doesn't wire it up correctly?
>>> I set ProcessAllSections = true, but I didn't recognize any change. I
>>> found that RuntimeDyLdCOFF does not override finalizeLoad like the ELF
>>> and MachO versions. The function call's comment reads "Give the
>>> subclasses a chance to tie-up any loose ends" -- possibly missing
>>> functionality?
>>>
>>> It would help a lot if you let me know your feeling on this issue and/or
>>> give me a few pointers what I could check next.
>>>
>>> I can reproduce the above symptoms reliably within our project on
>>> different Windows systems. I think I can also prepare a self-contained
>>> repro, if you happen to have a Windows machine/VM at hand and you are
>>> interested in clearing up this issue.
>>>
>>> Thanks.
>>> Stefan
>>>
>> _______________________________________________
>> LLVM Developers mailing listllvm-dev at lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>> -- https://about.me/stefan.graenitz
>>
>> -- https://about.me/stefan.graenitz
>
> -- https://about.me/stefan.graenitz
>
>
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