Assignment 3 ELF Loader

Main idea

• When the executable is started is generates page faults for each memory acces to a new page.
• There is a signal handler that gets triggered every time a page fault is generated.
• The signal handler first has to see in which segment the page fault occured.
  • This is done in signal_handler by comparing the address at which the page fault occured to the start address and end address of each segment
  • If there is no segment then it's a true invalid acces and Segmentation fault is delivered
• After the segment is found, we have to find informations about the page that contains the address of the page fault
• If the page was already mapped then the access didn't have the right permisions and Segmentation fault is delivered
• If the page isn't mapped then we map it:
  • For bss address we map with the MAP_ANONYMOUS flag on
• To see what kind of mapping it has to be made we compare the page_start and page_end to the file_size of that segment
  • If file_size is between those two then the page could have .bss data as well and we have to map accordingly