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

Minimum shelf, At a shop of marbles, packs of marbles are prepared. Packets...

At a shop of marbles, packs of marbles are prepared. Packets are named A, B, C, D, E …….. All packets are kept in a VERTICAL SHELF in random order. Any numbers of packets with thes

Explain scope rules and storage classes, Scope Rules and Storage Classes ...

Scope Rules and Storage Classes The storage class verifies the life of a variable in terms of its duration or its scope. There are four storage classes : automatic static

Atm program, Ask quIn this assignment you will create an ATM Machine progra...

Ask quIn this assignment you will create an ATM Machine program (using C++) that allows a user to choose one of the following introduction menu items: 1) Create a bank account by

What do you mean by inheritance, Inheritance is the process of forming new ...

Inheritance is the process of forming new classes, called derived classes, from existing classes or base classes. The derived class inherits all the capabilities of the base class,

Introduction of c, Discuss the saleint featuresand application of c

Discuss the saleint featuresand application of c

Pascal programming , 1. The management of a company would like to determine...

1. The management of a company would like to determine the median annual salary of its employees.Write a pascal program that display the number of employees and their median salary

Polishing game, Byteland county is very famous for luminous jewels. Luminou...

Byteland county is very famous for luminous jewels. Luminous jewels are used in making beautiful necklaces. A necklace consists of various luminous jewels of particular colour. Nec

Explain syntax rules for writing a destructor function, Syntax rules for wr...

Syntax rules for writing a destructor function Its name is the similar as that of the class to which it belongs, except that the first character of the name is the symbol t

Boardcoloring, how to fill the blank spaces in the board of 4*4 matrix with...

how to fill the blank spaces in the board of 4*4 matrix with the minimum of 4 colors and the condition is the adjacent element should not have the same colour

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