Can any one solve this Problem...!!! Post: 83484

Sponsored Content

Top Forums Programming Can any one solve this Problem...!!! Post 83484 by Perderabo on Thursday 15th of September 2005 09:51:04 AM

09-15-2005

Administrator Emeritus

A solution involving portable C eludes me! I naturally rejected the idea of having change() locate its return address on the stack and alter it to step over the i=10 statement. The precise location of the return address and even whether to increment it or decrement it and certainly by how much can vary from system to system. There is really no guarantee that the return address will be stored on the stack or even that there is a stack. I admit that I don't know of any currently marketed unix systems without a stack or that move the PC backwards. But I also don't know of any standard prohibiting them. These days we are in transistion from 32 bit to 64 bit architectures. Most versions of unix currently support executables in either architecture. So the change() function would need to detect the length of the return address as well.

But the other problem that I see with this involves agressive optimization. There is no indication that i is accessible to change() or is otherwise aliased or volatile. So there is no reason that the compiler writer could not legally choose to emit code that operates like...
i=10;
change();
printf("%d",i);
Whether or not that would happen would probably depend on the optimization level selected and the compiler used, and whether or not the resulting executable is intended to interact with a symbolic debugger.

So if you have a portable solution, I would love to see it!

Perderabo

View Public Profile for Perderabo

Find all posts by Perderabo

9 More Discussions You Might Find Interesting

1. Programming

How can I solve this problem?

I'm now designing a server application which can serve large number of clients' request. I've a question to ask, that is, main process will block when invoke the "accept" function, if a client request comes, main process should be separated into 2 processes by invoking "fork" function, the parent...

2. UNIX for Advanced & Expert Users

can't solve that problem [PLEASE HELP]

well, my internet brakes down every day because of my server, i don't have troubles with RAM or anything i think... that problem started since i am running an unrealircd server... well, my internet brakes down and when i try to access the inside ip from the server on http port 80, it says that:...

3. UNIX for Advanced & Expert Users

use two unix commands to solve the following problem

Hi, all, The following commands could compute the 10 most frequent bigrams from a input sequence which is in a file infile. I would like to know whether there is somebody who can use only two unix commands to do the same work. -------------------- tr " " "\012*" <infile >out1 tail +2...

4. UNIX for Advanced & Expert Users

How to solve restarting problem

Hi! My unix os version is OSF1 CP1 V4.0 878 alpha. It startup normally but it restarts within 5 sec. I would like to know how to solve . Please reply to me. Thanks . akzin

5. IP Networking

Need to solve complex network problem

I have a Red Hat linux server X on a x.x.0.0 network. This machine also has to communicate with another server Y on a network called y.y.0.0 Server X has two network interfaces. eth0 is configured on the x.x.0.0 network and has a default gateway on the x.x.0.0 network. In order to...

6. UNIX for Advanced & Expert Users

how would you solve this problem?

I have a file process.txt I wanted to just grab data in "process" column. Name process process_id status Adminserver adminserver 22669 Running Browser Engine browserengine ...

7. Shell Programming and Scripting

Unknown Problem. I really want your help to solve this!

Take a look on this code: #!/bin/sh currentpath=`pwd` if ; then #Normal user if ; then "$currentpath"/.cleaner else ./runit fi else #Root user if ; then rm -r /some fi mkdir /some cd /home/ echo "`ls --group-directories-first -1`" > /some/allusers cat /some/allusers | sed 's/...

8. Shell Programming and Scripting

How to solve the problem of overwriting an array?

Hi all, I have a file..... I want to print 2nd column arranged according to order of first column, present in second file..... So, the output should be: I am using following code: awk 'NR==FNR{a=$2;next}{print a?a:"ABSENT\t"}' file1 file2 But, it seems that the...

9. Shell Programming and Scripting

Help me solve this scripting problem please

LEARN ABOUT SUNOS

setustack

getustack(2)							   System Calls 						      getustack(2)

NAME

       getustack, setustack - retrieve or change the address of per-LWP stack boundary information

SYNOPSIS

       #include <ucontext.h>

       int getustack(stack_t **spp);

       int setustack(stack_t *sp);

DESCRIPTION

       The  getustack() function retrieves the address of per-LWP stack boundary information.  The address is stored at the location pointed to by
       spp. If this address has not been defined using a previous call to setustack(), NULL is stored at the location pointed to by spp.

       The setustack() function changes the address of the current thread's stack boundary information to the value of sp.

RETURN VALUES

       Upon successful completion, these functions return 0. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       These functions will fail if:

       EFAULT	       The spp or sp argument does not refer to a valid address.

USAGE

       Only implementors of custom threading libraries should use these functions to get and set the address of the stack  bound  to  an  internal
       per-thread data structure. Other users should use stack_getbounds(3C) and stack_setbounds(3C).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |       ATTRIBUTE TYPE	     |	     ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     | Evolving 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     | Async-Signal-Safe	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       _stack_grow(3C), stack_getbounds(3C), stack_inbounds(3C), stack_setbounds(3C), stack_violation(3C), attributes(5)

SunOS 5.10							    2 Nov 2004							      getustack(2)