segmentation fault
Hi,
I'm writing a C program in Linux to display memory content of BIOS data area at segement 0040h with offset 0013h. Below is my program:
#include <stdio.h>
int *ptr;
int main(void)
{
ptr = 00400013
printf("\nContent is %d\n", *ptr);
return 0;
}
When I ran this program, I got this error "segmentation fault". Does it related to protected mode in Linux? If so, what can I do?
> Does it related to protected mode in Linux?
Yes - you can't point at random bits of real memory anymore
> If so, what can I do?
State what it is you are actually trying to do.
I'm not even sure if linux even bothers with the BIOS data area (as it is used from say DOS).
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
When a PC boots up, some memory areas are reserved to contain initialization data. I want to access and display information on these specific memory addresses. Any possible solution in Linux?
I am pretty sure you would have to write a kernel module. I don't think linux would let you do it any other way. I am going to have to ask my brother though. He'll know. He'll probably post next
Muhahah <posting to prove linuxdude wrong>
Why are you declaring the pointer as a global btw?
linux doesn't deal with BIOS data structures, like dos.
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Well if you really want to go looking in physical memory, then start with reading
man 4 mem
Which tells you all about reading the /dev/mem file.
But like I (and others) have said, I don't think the BIOS information will be there. Sure it may write some stuff there when the machine starts, but once Linux takes over, I don't think the BIOS plays any further part, so that memory gets claimed by the OS for it's own use.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Salem,
Do you mean that Linux overwrites the contents of these memory areas?
Download the source for the kernel and find out
Write a program using /dev/mem and find out
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Well, what the others have said, but I'd like to point out the errors in the program. When you're assigning 00400013 to the pointer, there is a problem with the base you're using.
You want to use hexadecimal number base, and you're in fact using octal. Any number that starts with a 0 is treated as octal, and the actual memory location you're accessing is way off. You'd need to use 0x00400013. Any number that starts with 0x (that's a zero, same with octal) is treated as hexadecimal.
I just thought I'd point that out.
SoKrA-BTS "Judge not the program I made, but the one I've yet to code"
I say what I say, I mean what I mean.
IDE: emacs + make + gcc and proud of it.
