Project 1

• In this project, you need to write a new system call void * my_get_physical_addresses(void *) so that a process can use it to get the physical address of a virtual address of a process.
• The return value of this system call is either 0 or an address value. 0 means that there is no physical address assigned to the logical address currently. A non-zero value means the physical address of the logical address submitted to the system call as its parameter (in fact, this address is only the offset of a logical address).

                 //prototype of the new system call is as follows:     

                 void * my_get_physical_addresses(void *)
               
              

                 #include <stdio.h>
                

                 //void * my_get_physical_addresses(void *);



                 int global_a=123;  //global variable

                 void hello(void)
                 {                    
                    printf("======================================================================================================\n");
                 }  


                 int main()
                 { 
                   int      loc_a;
                   void     *parent_use, *child_use;  

                   printf("===========================Before Fork==================================\n");             
                   parent_use=my_get_physical_addresses(&global_a);
                   printf("pid=%d: global variable global_a:\n", getpid());  
                   prinft("Offest of logical address:[%p]   Physical address:[%p]\n", &global_a,parent_use);              
                   printf("========================================================================\n");  

                   
                   if(fork())
                   { /*parent code*/
                     printf("vvvvvvvvvvvvvvvvvvvvvvvvvv  After Fork by parent  vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv\n"); 
                     parent_use=my_get_physical_addresses(&global_a);
                     printf("pid=%d: global variable global_a:\n", getpid()); 
                     prinft("******* Offset of logical address:[%p]   Physical address:[%p]\n", &global_a,parent_use); 
                     printf("vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv\n");                      
                     wait();                    
                   }
                   else
                   { /*child code*/

                     printf("llllllllllllllllllllllllll  After Fork by child  llllllllllllllllllllllllllllllll\n"); 
                     child_use=my_get_physical_addresses(&global_a);
                     printf("******* pid=%d: global variable global_a:\n", getpid());  
                     prinft("******* Offset of logical address:[%p]   Physical address:[%p]\n", &global_a, child_use); 
                     printf("llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll\n");  
                     printf("____________________________________________________________________________\n");  

                     /*----------------------- trigger CoW (Copy on Write) -----------------------------------*/    
                     global_a=789;

                     printf("iiiiiiiiiiiiiiiiiiiiiiiiii  Test copy on write in child  iiiiiiiiiiiiiiiiiiiiiiii\n"); 
                     child_use=my_get_physical_addresses(&global_a);
                     printf("******* pid=%d: global variable global_a:\n", getpid());  
                     prinft("******* Offset of logical address:[%p]   Physical address:[%p]\n", &global_a, child_use); 
                     printf("iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii\n");  
                     printf("____________________________________________________________________________\n");                  
                     sleep(1000);
                   }
                 }

                

                 #include <stdio.h>
                

                 //void * my_get_physical_addresses(void *);



                 int a[2000000]; 
                 


                 int main()
                 { 
                   int      loc_a;
                   void     *phy_add;  

                          
                   phy_add=my_get_physical_addresses(&a[0]);
                   printf("global element a[0]:\n", );  
                   prinft("Offest of logical address:[%p]   Physical address:[%p]\n", &a[0], phy_add);              
                   printf("========================================================================\n"); 
                   phy_add=my_get_physical_addresses(&a[1999999]);
                   printf("global element a[1999999]:\n", );  
                   prinft("Offest of logical address:[%p]   Physical address:[%p]\n", &a[1999999], phy_add);              
                   printf("========================================================================\n"); 
     

                 }

                

• Two threads show a physical memory cell (one byte) if both of them have a virtual address that is translated into the physical address of the memory cell.
• The kernel usually does not allocate physical memories to store all code and data of a process when the process starts execution.
• Inside the Linux kernel, you need to use function copy_from_user() and function copy_to_user() to copy data from/to a user address buffer.
• Check the "Referenced Material" part of the Course web site to see how to add a new system call in Linux.