1. Displaying Memory/Files
What every systems programmer needs to know how to do

2. An often-needed capability
When we want to look at memory-contents
or see what’s been saved in an arbitrary file
We need to write code for a memory-dump
So often, It’s probably worth memorizing!

3. Here’s the basic loop in C
unsigned char *cp; // where the data starts
int n; // number of bytes of data
for (i = 0; i < n; i += 16) {
if ( (i % 16) == 0 ) printf( “\n%a: “, cp+i );
for (j = 0; j < 16; j++)
{ if ( i+j < n ) printf( “%02X “, cp[i+j] ); else printf( “ “ ); }
char ch = ( i+j < n ) ? cp[i+j] | 0x20;
if (( ch < 0x20 )||( ch > 0x7E )) ch = ‘.’;
printf( “%c”, ch ); }

4. Exercise: let’s see our stack
Write a program to ‘dump’ its user-stack
We can use inline assembly to get ESP
int main( void ) {
unsigned char *cp;
asm(“ movl %%esp, %0 “ : “=n” (cp) );
int nbytes = 0xC – (int)cp;
/* then code to dump stack goes here */

5. Compare with ‘mm_struct’
Header-file ‘/usr/src/linux/include/linux/sched.h’
Defines the type ‘struct mm_struct’
Includes some fields describing user stack