lib/pgfault.c

   1 // User-level page fault handler support.
   2 // We use an assembly language wrapper around a C function.
   3 // The assembly wrapper is in pfentry.S.
   4
   5 #include <inc/lib.h>
   6
   7
   8 // Assembly language pgfault entrypoint defined in lib/pgfaultentry.S.
   9 extern void _pgfault_upcall(void);
  10
  11 // Pointer to currently installed C-language pgfault handler.
  12 void (*_pgfault_handler)(struct UTrapframe *utf);
  13
  14 //
  15 // Set the page fault handler function.
  16 // If there isn't one yet, _pgfault_handler will be 0.
  17 // The first time we register a handler, we need to
  18 // allocate an exception stack (one page of memory with its top
  19 // at UXSTACKTOP), and tell the kernel to call the assembly-language
  20 // _pgfault_upcall routine when a page fault occurs.
  21 //
  22 void
  23 set_pgfault_handler(void (*handler)(struct UTrapframe *utf))
  24 {
  25         int r;
  26
  27         if (_pgfault_handler == 0) {
  28                 // First time through!
  29                 // LAB 4: Your code here.
  30                 if ((r = sys_page_alloc(0, (void *)(UXSTACKTOP-PGSIZE),
  31                                                                 PTE_U | PTE_W | PTE_P)) < 0)
  32                         panic("set_pgfault_handler: page alloc error: %e", r);
  33         }
  34
  35         // Save handler pointer for assembly to call.
  36         _pgfault_handler = handler;
  37
  38         // register the env pgfault upcall
  39         if ((r = sys_env_set_pgfault_upcall(0, _pgfault_upcall)) < 0)
  40                 panic("set_pgfault_handler: set pgfault upcall error: %e", r);
  41 }
  42