[LLVMdev] bug in the JIT global variable emitter

[Nuno Lopes]

[resending since the previous copy was apparently dropped by the mailing 
list]

>> Today I found a nice bug in the JIT global variable emitter.
>> The problem may lead to an assert() failure when doing the following:
>> 1) compile some function
>> 2) emit a global variable
>> 3) compile another function. an assert() may trigger in the JIT memory
>> manager
>>
>> This happens because the JIT global variable emitter is using the
>> MachineCodeEmitter::allocate() function, which uses memory allocated
>> by the
>> JIT memory manager (which should be used for functions only).
>
> No, this was a deliberate change, 54442.  We have a situation where a
> user
> wants to emit JIT code on one machine, then send it off to another
> machine to
> execute.  Putting statically allocated data in the same buffer as code
> is the
> easiest approach to make this work, although there may be others.

Ok, thanks for the explanation. So my first patch doesn't work. Also, to be
clear, this bug has nothing to do with overflowing the JIT memory buffer.
I made another one that takes keeps the allocation of global variables in
the JIT buffer, but it creates a new mem block if it doesn't exist (i.e.
when dumping a global variable out of the scope of a function compilation).
The patch is at:
http://web.ist.utl.pt/nuno.lopes/llvm_jit_global_emitter2.txt

The problem only happens when calling
ExecutionEngine::getPointerToGlobal(someGV) from some non-llvm program. If
the function is called when JITing a function, it works, since it will dump
the global variable to the memory reserved to the function being JITed,
which raises a question: shouldn't it generate the GV to some non-executable
memory block?? My patch doesn't attempt to fix this last concern.

Thanks,
Nuno

P.S.: the control flow of this bug is quite complex, so feel free to ask if
you don't get what the problem is.