Functions and stack frame, C/C++ Programming

Assignment Help:

Each function has its own stack frame between %fp and %sp. Let Caller calls Callee. Then Caller's %sp becomes callee's %fp, and callee's %sp set to be a new value (a smaller one because stack grows from large address to small address). You can think that Callee's stack frame is on top of Caller's stack frame.

In Caller: put arguments in %o0 to %o5 registers or if number of arguments more than 6, prepare values in call linkage of the current stack frame. Then "call" address_of_callee; %o7 stored the returned address. (This %o7 will becomes %i7 in callee after the callee executes save instruction.)

In Callee: it executes "save" instruction:

  • 0. Caller's %i (input registers) and %l (local registers) are reserved in its own stack frame. They are put in the top portion of the caller's stack frame. Implication: the return address of Caller (NOT CALLEE), %i7, is stored there.
  • 1. set callee's %i (input registers) by callers %o (output registers). The implication: pass parameters and return address now is in %i7. And now callee's fp (%i6) <-- caller's sp (%o6).
  • 2. Allocate space for new frame pointers. Caller's sp (%o6) is now set to be the new value.

So at this point in callee, %i6 (%fp was caller's %o6) is set, and %o6 (%sp is set to be a new value). Question: where is the old %fp? It is stored somewhere in the top portion of the previous stack frame (see step 0.) The return address of Callee is stored in %i7. Is it possible to write a program to overflow this %i7? What return address that you really can overflow? Question: how to access that return address.

The "restore" instruction is the inverse function of save. Then the "ret" instruction should branch to %i7+8. The normal address should be %i7+4 as the next instruction address after call. The extra 4 is because sparc has a "branch delay" instruction that is executed BEFORE the call is made even it is put just after CALL. Is it strange. Not really. This is because modern CPU is a pipeline machine. It loads instruction every clock cycle, and branch (or jump or call) somewhat cannot be really done until the later stage the pipeline. And then it is already too late because the one JUST after this branch has already been executed. If you want to know more, you should take a look at computer architecture textbook which I think every graduate should know.

You should be very clear what return address in server.c is overflowed? Is it the return address of main() or the return address of copy()?


Related Discussions:- Functions and stack frame

Integration, to find the area under the curve y = f(x) between x = a and x ...

to find the area under the curve y = f(x) between x = a and x = b

Program, write a program for convert numbers upto 9 to alphabet?Eg.now ente...

write a program for convert numbers upto 9 to alphabet?Eg.now enter the inputis 666 means output is "0" lphabet

Fill an array of randomly generated integers, The task consists of two part...

The task consists of two parts which are both preferably implemented in one source file. Towards the end of this document you will find a code skeleton that you must assume. Start

Function with two arguments, Write out pseudocode for a function called "an...

Write out pseudocode for a function called "and" that takes two arguments, both booleans, and returns the logical and of the inputs. DO NOT use the logical and operator: instead, w

Bitcoin alternative – deployment and modification, I started preparing an a...

I started preparing an alternative cryptocurrency and I am way over my head. I would like help in making modifications to the open source files and then help with deployment. I wil

Area under the curve, Write a c++ program to find the area under the curve ...

Write a c++ program to find the area under the curve y = f(x) between x = a and x = b, integrate y = f(x) between the limits of a and b. The area under a curve between two points c

Polindrome, A palindrome is a string that reads the same from both the ends...

A palindrome is a string that reads the same from both the ends. Given a string S convert it to a palindrome by doing character replacement. Your task is to convert S to palindrome

Molecular dynamics and Monte carlo, Molecular dynamics for a Lennard-Jones ...

Molecular dynamics for a Lennard-Jones system (in C++) 1. Write a function which reads in the input variables of a molecular dynamics simulation of a Lennard-Jones system. The inpu

What are user defined data types, Q: What are User Defined data types? ...

Q: What are User Defined data types? C supports an extraordinary feature known as "type definition" that permits users to define an identifier that would represent an existing

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd