memlayout.c

#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>
#include <unistd.h>
#include <signal.h>
#include "memlayout.h"

// Storing the current memory access type
static sig_atomic_t current_access, last_access;

// Storing where to return after the signal handlers
static sigjmp_buf jumpbuf;

// For making sure the process controlling this doesn't get affected.
static struct sigaction oldsignalhandle;
static struct sigaction oldsignalbushandle;
static struct sigaction newsignalhandle;

// Signal handler for SIGSEGV
static void handler(int signum) {
	siglongjmp(jumpbuf, 1);
}

// Memory scan function
int get_mem_layout (struct memregion *regions, unsigned int size){
	
	// Saving the old signal handler of mem_x.c files
  	if( sigaction(SIGSEGV, NULL, &oldsignalhandle) == -1){
		printf("Failed saving old SIGSEGV handler.");
		exit(EXIT_FAILURE);
	}
	if( sigaction(SIGBUS, NULL, &oldsignalbushandle) == -1){
		printf("Failed saving old SIGSEGV handler.");
		exit(EXIT_FAILURE);
	}

	// Defining new sigaction struct
	newsignalhandle.sa_flags = 0; // no flags
	sigemptyset(&newsignalhandle.sa_mask); // clear the mask so no signals are blocked
	newsignalhandle.sa_handler = handler; // set function pointer for handler
	
	// Setting the signal handlers
	sigaction(SIGSEGV, &newsignalhandle, NULL); // set the handler
	sigaction(SIGBUS, &newsignalhandle, NULL); // set the handler

  	unsigned int *currentAddress = 0; // This is the current address we are in for the search.
  	int readValue; // This is the value in the currentAddress	
	int pageSize = PAGE_SIZE; // Page size of a memory space
	int listIndex = 0; // The current index in regions
	int regionCount = 0; // The total count of regions
	int isItFirst = 1; // Active in currentAddress = 0x0
	
	int i;
	int needTimes = ((0xFFFFFFFF - pageSize + 1) / pageSize) + 1; // This is how many times we scan with the pagesize

	for( i = 0; i < needTimes; i++ ){
		current_access = MEM_NO;
        if ( sigsetjmp(jumpbuf, 1 ) == 0 ){
            // Reading operation
            readValue = *currentAddress;
            current_access = MEM_RO;	

            // Writing operation 
            *currentAddress = readValue;
            current_access = MEM_RW;			
        }	

		// Putting the values into the array
		if(isItFirst){
			regions[listIndex].from = currentAddress;
			regions[listIndex].to = (int*)((int)currentAddress + pageSize - 1);
			regions[listIndex].mode = current_access;
			isItFirst = 0;
			regionCount++;
		}else{
			if(listIndex < size-1){
				if(current_access != last_access){
					listIndex ++;
					regions[listIndex].from = currentAddress;
					regions[listIndex].to = (int*)((int)currentAddress + pageSize - 1);
					regions[listIndex].mode = current_access;
				}else{
					regions[listIndex].to = (int*)((int)currentAddress + pageSize - 1);
				}
			}
			if(current_access != last_access){
				regionCount++;
			}
		}

		last_access = current_access;
		currentAddress = currentAddress + (pageSize>>2); // It is a int addition to pointer. 
    }

	// Filling out the rest if size > regionCount
	while(listIndex < size){
		regions[listIndex].mode = MEM_NO;
		listIndex++;
	}

	// Loading the old signal handler of mem_c files
	sigaction(SIGSEGV, &oldsignalhandle, NULL);
	sigaction(SIGSEGV, &oldsignalbushandle, NULL);
    return regionCount;
}