09-15-2005
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!
9 More Discussions You Might Find Interesting
1. Programming
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... (4 Replies)
Discussion started by: acqy
4 Replies
2. UNIX for Advanced & Expert Users
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:... (2 Replies)
Discussion started by: AiRkO
2 Replies
3. UNIX for Advanced & Expert Users
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... (3 Replies)
Discussion started by: vicky20000
3 Replies
4. UNIX for Advanced & Expert Users
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 (2 Replies)
Discussion started by: akzin
2 Replies
5. IP Networking
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... (4 Replies)
Discussion started by: soliberus
4 Replies
6. UNIX for Advanced & Expert Users
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 Replies)
Discussion started by: soemac
7 Replies
7. Shell Programming and Scripting
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/... (17 Replies)
Discussion started by: hakermania
17 Replies
8. Shell Programming and Scripting
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... (3 Replies)
Discussion started by: CAch
3 Replies
9. Shell Programming and Scripting
Hello,
I would really appreciate some help into approaching this problem:
- i have a random txt file with x lines and y rows following this pattern:
ex:
ip1 | user1 | command
ip2 | user2 | command
ip3 | user3 | command
- i need to telnet/ssh into these ip's, login with... (7 Replies)
Discussion started by: catalinstk
7 Replies
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)