Alloca implementation

Question

How does one implement alloca() using inline x86 assembler in languages like D, C, and C++? I want to create a slightly modified version of it, but first I need to know how

Answer 1

It would be tricky to do this - in fact, unless you have enough control over the compiler's code generation it cannot be done entirely safely. Your routine would have to manipulate the stack, such that when it returned everything was cleaned, but the stack pointer remained in such a position that the block of memory remained in that place.

The problem is that unless you can inform the compiler that the stack pointer is has been modified across your function call, it may well decide that it can continue to refer to other locals (or whatever) through the stack pointer - but the offsets will be incorrect.