Why not a segmentation fault??


 
Thread Tools Search this Thread
Top Forums Programming Why not a segmentation fault??
# 1  
Old 05-08-2008
Why not a segmentation fault??

Hi,

Why I don't receive a segmentation fault in the following sample.

int main(void)
{
char buff[10];
sprintf(buff,"Hello world");
printf("%s\n",buff);
}

If I define a buffer of 10 elements and I'm trying to put inside it twelve elements, Should I receive a sigsev signal???

Thanks in advance!
# 2  
Old 05-08-2008
Actually, not quite.
SegFault (in this case) goes when the EIP register point's to a invalid memory address to execute, and just 2 bytes aren't enough to reach the EIP, however try with 500 chars Smilie, you should get your SegFault.
# 3  
Old 05-08-2008
Thanks!

Hi Zarnick,

So, you mean that when I overwrite the return instruction pointer on the procedure stack I should receive a SegFault, but if I don't reach it I don't? and why not 2 bytes aren't enough??

Sorry, I don't want to be annoying!

Thanks!!
# 4  
Old 05-08-2008
snprintf() anyone

Another reason to use snprintf() instead of sprintf() because sprintf() does not check for bounds.
# 5  
Old 05-08-2008
I wouldn't know for sure why 2 bytes are just not enough, I think it's something to do with the pointers used to allocate the enough memory for your char[10] string. But I can be wrong on this one.

And at least from what I can remember, I never saw a segfault that wasn't about the EIP register being overruned, as always, I can be wrong.
# 6  
Old 05-08-2008
Shamrock -
He is trying to create a SIGSEGV. To test some other code. This corrupts the stack on HPUX PA_RISC boxes, and then dumps core:
Code:
#include <stdlib.h>
#include <string.h>

int main()
{
	char buff[10]={0x0};
	char *p=buff;
	p-=20;
    memset(p,0x0, sizeof(buff));
    return 0;	
}

# 7  
Old 05-08-2008
Thanks!

Hi All,

Certainly I'm fixing an application with this type of code and I've replaced the sprintf by snprintf function, but I have to explain to my boss why I'm doing it and I need to show him the application crashing.

The original message in the printf function overcomes the boundaries only for 2 bytes and it doesn't crash, I don't know how to do it and I don't know if its behavior is deterministic or not.

Thanks to all of you for your support!!!!!
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. Programming

C. To segmentation fault or not to segmentation fault, that is the question.

Oddities with gcc, 2.95.3 for the AMIGA and 4.2.1 for MY current OSX 10.14.1... I am creating a basic calculator for the AMIGA ADE *NIX emulator in C as it does not have one. Below are two very condensed snippets of which I have added the results inside the each code section. IMPORTANT!... (11 Replies)
Discussion started by: wisecracker
11 Replies

2. Programming

Segmentation fault

I keep getting this fault on a lot of the codes I write, I'm not exactly sure why so I'd really appreciate it if someone could explain the idea to me. For example this code #include <stdio.h> main() { unsigned long a=0; unsigned long b=0; int z; { printf("Enter two... (2 Replies)
Discussion started by: sizzler786
2 Replies

3. Homework & Coursework Questions

Segmentation Fault

this is a network programming code to run a rock paper scissors in a client and server. I completed it and it was working without any error. After I added the findWinner function to the server code it starts giving me segmentation fault. -the segmentation fault is fixed Current problem -Also... (3 Replies)
Discussion started by: femchi
3 Replies

4. Programming

Using gdb, ignore beginning segmentation fault until reproduce environment segmentation fault

I use a binary name (ie polo) it gets some parameter , so for debugging normally i do this : i wrote script for watchdog my app (polo) and check every second if it's not running then start it , the problem is , if my app , remain in state of segmentation fault for a while (ie 15 ... (6 Replies)
Discussion started by: pooyair
6 Replies

5. Programming

segmentation fault

Hi, I am having this segmentation fault not in the following program, bt. in my lab program . My lab program is horrible long so cannot post it here bt. I am using the following logic in my program which is giving the segmentation fault. Bt. if I run this sample program as it is it dosen't give... (3 Replies)
Discussion started by: mind@work
3 Replies

6. UNIX for Dummies Questions & Answers

Segmentation Fault

Hi, While comparing primary key data of two tables thr bteq script I am getting this Error. This script is a shell script. *** Error: The following error was encountered on the output file. Script.sh: 3043492 Segmentation fault(coredump) Please let me know how to get through it. ... (5 Replies)
Discussion started by: monika
5 Replies

7. AIX

Segmentation fault

Hi , During execution a backup binary i get following error "Program error 11 (Segmentation fault), saving core file in '/usr/datatools" Riyaz (2 Replies)
Discussion started by: rshaikh
2 Replies

8. Programming

segmentation fault

ive written my code in C for implementation of a simple lexical analyser using singly linked list hence am making use of dynamic allocation,but when run in linux it gives a segmentation fault is it cause of the malloc function that ive made use of????any suggestions as to what i could do??? thank... (8 Replies)
Discussion started by: rockgal
8 Replies

9. Programming

Hi! segmentation fault

I have written a program which takes a directory as command line arguments and displays all the dir and files in it. I don't know why I have a problem with the /etc directory.It displays all the directories and files untill it reaches a sub directory called peers which is in /etc/ppp/peers.the... (4 Replies)
Discussion started by: vijlak
4 Replies

10. UNIX for Dummies Questions & Answers

Segmentation Fault

hello all, I tried a program on an array to intialise array elements from the standard input device.it is an integer array of 5 elements.but after entering the 4th element it throws a message called "Segmentation Fault" and returns to the command prompt without asking for the 5th element. ... (3 Replies)
Discussion started by: compbug
3 Replies
Login or Register to Ask a Question