[LLVMdev] Exception handling question
junk at giantblob.com
Fri Jan 22 11:08:13 CST 2010
2010/1/22 Garrison Venn <gvenn.cfe.dev at gmail.com>
> Hi James,
> Note that the wiki example is a manual JIT example that works directly with
> the C++ APIs. As you know, no LLVM tools are used,
> just LLVM libraries. I say this to point out, that in the example, the
> exception mechanism is under the complete control of the
> developer moded by the LLVM libraries. In my mind a different
> example/different doc. would be needed to explain how
> a bit code driven JIT exception mechanism works. Sure the semantics and
> syntax of the unwind mechanism would be the
> same, but how/where the dwarf is emitted could be different. I do know that
> different classes are used to emit dwarf code
> for non-JIT projects vs what classes are used in the wiki JIT example. I
> know you understand this already, but I just wanted to
> make it clear for the readers of this list.
In principle though what I'm trying to do ought to work though - I don't see
anything fundamentally different about my bitcode test that lli loads from a
file versus what the wiki JIT exception example generates at runtime. Both
should result in similar IR in memory driving the JIT to generate the
required unwind information from inkove instructions and the llvm.eh
intrinsics - there's no other magic going on in the JIT example (is there?)
Anyway, I now have LLVM trunk from svn compiled with debug information,
which makes it easier to see what's going on. Assuming I get to the bottom
of it I'll post an update here.
> PS: I would find if extremely useful, if you would post your results once
> you've figured out the issues.
> On Jan 22, 2010, at 10:31, James Williams wrote:
> 2010/1/22 James Williams <junk at giantblob.com>
>> 2010/1/22 Duncan Sands <baldrick at free.fr>
>>> Hi James,
>>> want to send us your testcase code? Then we can give it a whirl.
>>>> Test code is at http://giantblob.com/ehtest.tar.gz
>>>> Thanks for the help. I apologize in advance if it turns out I'm doing
>>>> something stupid!
>>> I hope you realise that by running llvm-ld without -native you are
>>> executing your program from the JIT. I did a native compilation as
>>> used llvm-link to link all of the bitcode into "total.bc"; ran llc on
>>> producing "total.s"; did "g++ -o total total.s"; ran ./total. It seems
>>> to work:
>>> $ ./total
>>> __l_personality called$
>>> Of course it is probably supposed to work from the JIT too (I don't know
>>> anything about the JIT), but it clearly doesn't: when I tried I got:
>>> lli: lib/ExecutionEngine/JIT/JIT.cpp:624: void
>>> llvm::JIT::runJITOnFunctionUnlocked(llvm::Function*, const
>>> llvm::MutexGuard&): Assertion `!isAlreadyCodeGenerating && "Error: Recursive
>>> compilation detected!"' failed.
>>> 6 lli 0x0000000000d3f5e2
>>> llvm::JIT::runJITOnFunctionUnlocked(llvm::Function*, llvm::MutexGuard
>>> const&) + 62
>>> 7 lli 0x0000000000d3f9c6
>>> llvm::JIT::getPointerToFunction(llvm::Function*) + 686
>>> 8 lli 0x0000000000d67c86
>>> llvm::ExecutionEngine::getPointerToGlobal(llvm::GlobalValue const*) + 70
>>> 9 lli 0x0000000000d62805
>>> llvm::JITDwarfEmitter::EmitCommonEHFrame(llvm::Function const*) const + 613
>>> 10 lli 0x0000000000d60ac3
>>> llvm::JITCodeEmitter&, unsigned char*, unsigned char*, unsigned char*&) +
>> Thanks for looking at this.
>> Yes, I realise this will link to bitcode and that the result is a script
>> that runs lli. I kind of just expected JIT to work, particularly since the
>> example code on the wiki uses JIT.
>> The JIT is what my project will eventually target (goal is an out of
>> process compiler will incrementally generate bitcode on disk combined with
>> an application server that will run resulting bitcode via JIT) and hence
>> I've only been testing on the JIT.
>> I'll see if I can work around the recursive compilation problem.
>> -- James
> Sorry - t's only just sunk in that the JIT must use a completely different
> mechanism to load the eh tables versus having as + ld and the ELF loader do
> it and that posting the assembler when I was seeing the JIT fail was
> probably unhelpful. I apologise for the confusion.
> -- James
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