[LLVMdev] Controlling the stack layout

[Bill Wendling]

Hi Nicolas,

>> This might help. See how "stack protectors" is implemented here:
>>
>> 	lib/CodeGen/StackProtector.cpp
>>
>> It places a special value at a specific place on the stack. You can
>> use the same trick to put your own information on a set stack
>> position. There's more to the code than just that .cpp file. It's  
>> done
>> with intrinsics. You'll also need to check out the
>> PrologEpilogInserter.cpp code.
>>
>>
> Thanks. I've already looked at what stack protector does, and indeed  
> the
> need is similar. However, I'd like to add the functionality as a new
> machine pass, so that I don't need to add new intrinsics and modify  
> the
> llvm code base. Do you think that's possible?
>
I suppose that it's possible, though not as elegant. :-) What type of  
information are you storing? Is it stuff that is known before we  
convert the LLVM IR into its DAG format for the back-end? If so, then  
it's probably cleaner to go the way of the stack protector. It's  
easier to send this information to the back-end so that it knows how  
to set up the prologue and epilogue. I'm not too familiar with the  
JIT, so I don't know if making this a machine function pass will work.

In all, modifying LLVM to create a new intrinsic (a la stack  
protectors) isn't all that much work. ;-) And modifying LLVM IR is  
*much* easier than modifying its DAG format.

-bw