[LLVMdev] Size limitations in MCJIT / ELF Dynamic Linker/ ELF codegen?

[Kaylor, Andrew]

I would guess that it's crashing somewhere in the generated code.  On Windows we don't have a way to get call stacks to the generated code (though if you want to try it on Linux, that should work).  You can probably look at the address where the crash is occurring and verify that it is in the generated code.

There are a couple of things I would look for.

First, I'd take a look at the SectionMemoryManager allocation handling.  The fact that the problem is code size dependent strongly points in this direction.  It may be that SectionMemoryManager does something wrong when it hits a page boundary or something.

Second, I'd look at the relocation processing.  If it is generating any stubs, that would be a potential problem spot, but it shouldn't be generating any stubs.  So the obvious thing to look at is whether any of the relocations are writing to the spot where the crash occurs.

-Andy


From: Yaron Keren [mailto:yaron.keren at gmail.com]
Sent: Tuesday, October 22, 2013 10:17 AM
To: Kaylor, Andrew
Cc: <llvmdev at cs.uiuc.edu>
Subject: Re: Size limitations in MCJIT / ELF Dynamic Linker/ ELF codegen?

OS is Windows 7 64 bit OS, compiler is 32 bit Visual C++ 2012 with 32 bit.
The target which is i686-pc-mingw32-elf so I can use the ELF dynamic loader.
Code model, relocation model and and memory manager are whatever default for this - did not modify.

The Module comes from clang. The source is 1000 or more lines repeating C++ code in one big function:

  A+1;
  A*B.t();

where A and B are matrices from Armadillo http://arma.sourceforge.net/. This a stress and performance test due to the large number of EH and temporary objects created.

I am using the Engine Builder and MCJIT unmodified (except the multi-modules patches which are not relevant as there is only one module) like this:

  OwningPtr<llvm::ExecutionEngine> EE(llvm::EngineBuilder(M)
                                          .setErrorStr(&Error)
                                          .setUseMCJIT(true)
                                          .create());

to run the function either

  llvm::Function *F = M->getFunction(Name);
  void *FN = EE->getPointerToFunction(F);
or
  uint64_t FN = EE->getFunctionAddress(Name);

followed by

 ((void (*)())FN)();
or
  EE->runFunction(F, std::vector<llvm::GenericValue>());

all work the same with smaller about 1000 lines of the above code module and crash the same with more code. The call stack is unhelpful Visual C++ says: Frames below may be incorrect and/or missing which indicates a real problem with it. I have tried to provide less stack space (default is 10M) for the compiled program without any change.

Yaron


2013/10/22 Kaylor, Andrew <andrew.kaylor at intel.com<mailto:andrew.kaylor at intel.com>>
I'm not aware of such a limitation.

What architecture, code model and relocation model are you using?  Are you using the SectionMemoryManager?

-Andy

From: Yaron Keren [mailto:yaron.keren at gmail.com<mailto:yaron.keren at gmail.com>]
Sent: Tuesday, October 22, 2013 8:12 AM
To: <llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>>; Kaylor, Andrew
Subject: Size limitations in MCJIT / ELF Dynamic Linker/ ELF codegen?

I'm running in MCJIT a module generated from one C++ function. Every line of the source function uses C++ classes and may throw an exception. As long as there are less than (about) 1000 lines, everything works. With more lines the compiled code crashes when running it, with no sensible stack trace.

Is there any kind of hard-coded size limitation in MCJIT / ELF Dynamic Linker / ELF codegen / number of EH states in a function ?

I did browse the code but could not find anything obvious.

Yaron


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