[LLVMdev] Controlling the stack layout

[Nicolas Geoffray]

Hi everyone,

As a front-end developer, I'd like to add a language-specific 
information at a fixed location of each stack frame. The reason is that 
I want to retrieve this information when dynamically walking the stack.

For example, X86 has the following stack layout for a function with two 
arguments and two locals:

12(%ebp)    - second function parameter
8(%ebp)      - first function parameter
4(%ebp)      - old %EIP (the function's "return address")
0(%ebp)      - old %EBP (previous function's base pointer)
-4(%ebp)     - first local variable
-8(%ebp)     - second local variable


I'd like to generate this layout:

12(%ebp)    - second function parameter
8(%ebp)      - first function parameter
4(%ebp)      - old %EIP (the function's "return address")
0(%ebp)      - old %EBP (previous function's base pointer)
-4(%ebp)     - My language specific information
-8(%ebp)     - first local variable
-12(%ebp)   - second local variable


Can I express this in LLVM without modifying llvm internals? I looked at 
writing a machine function pass, but I can't register one when JITting. 
Is the machine function pass the correct way of implementing this?

Thanks,
Nicolas