I know data in nested function calls go to the Stack.The stack itself implements a step-by-step method for storing and retrieving data from the stack as the functions get called or returns.The name of these methods is most known as Prologue and Epilogue.
I tried with no success to search material on this topic. Do you guys know any resource ( site,video, article ) about how function prologue and epilogue works generally in C ? Or if you can explain would be even better.
P.S : I just want some general view, not too detailed.
Prologue: (or preamble) Save registers and return address; transfer parameters. Epilogue: (or postamble) Restore registers; transfer returned value; return. A return statement in a procedure is compiled to: 1. Load the returned value into a register.
The definition of prologue introduce important information—such as background details, or characters—that have some connection to the main story, but whose relevance is not immediately obvious.
There are lots of resources out there that explain this:
to name a few.
Basically, as you somewhat described, "the stack" serves several purposes in the execution of a program:
The prolouge is what happens at the beginning of a function. Its responsibility is to set up the stack frame of the called function. The epilog is the exact opposite: it is what happens last in a function, and its purpose is to restore the stack frame of the calling (parent) function.
In IA-32 (x86) cdecl, the ebp
register is used by the language to keep track of the function's stack frame. The esp
register is used by the processor to point to the most recent addition (the top value) on the stack. (In optimized code, using ebp
as a frame pointer is optional; other ways of unwinding the stack for exceptions are possible, so there's no actual requirement to spend instructions setting it up.)
The call
instruction does two things: First it pushes the return address onto the stack, then it jumps to the function being called. Immediately after the call
, esp
points to the return address on the stack. (So on function entry, things are set up so a ret
could execute to pop that return address back into EIP. The prologue points ESP somewhere else, which is part of why we need an epilogue.)
Then the prologue is executed:
push ebp ; Save the stack-frame base pointer (of the calling function).
mov ebp, esp ; Set the stack-frame base pointer to be the current
; location on the stack.
sub esp, N ; Grow the stack by N bytes to reserve space for local variables
At this point, we have:
...
ebp + 4: Return address
ebp + 0: Calling function's old ebp value
ebp - 4: (local variables)
...
The epilog:
mov esp, ebp ; Put the stack pointer back where it was when this function
; was called.
pop ebp ; Restore the calling function's stack frame.
ret ; Return to the calling function.
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