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fault.c

/*
 *  linux/arch/m68k/mm/fault.c
 *
 *  Copyright (C) 1995  Hamish Macdonald
 */

#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#include <asm/setup.h>
#include <asm/traps.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>

extern void die_if_kernel(char *, struct pt_regs *, long);
extern const int frame_extra_sizes[]; /* in m68k/kernel/signal.c */

int send_fault_sig(struct pt_regs *regs)
{
      siginfo_t siginfo = { 0, 0, 0, };

      siginfo.si_signo = current->thread.signo;
      siginfo.si_code = current->thread.code;
      siginfo.si_addr = (void *)current->thread.faddr;
#ifdef DEBUG
      printk("send_fault_sig: %p,%d,%d\n", siginfo.si_addr, siginfo.si_signo, siginfo.si_code);
#endif

      if (user_mode(regs)) {
            force_sig_info(siginfo.si_signo,
                         &siginfo, current);
      } else {
            const struct exception_table_entry *fixup;

            /* Are we prepared to handle this kernel fault? */
            if ((fixup = search_exception_tables(regs->pc))) {
                  struct pt_regs *tregs;
                  /* Create a new four word stack frame, discarding the old
                     one.  */
                  regs->stkadj = frame_extra_sizes[regs->format];
                  tregs =     (struct pt_regs *)((ulong)regs + regs->stkadj);
                  tregs->vector = regs->vector;
                  tregs->format = 0;
                  tregs->pc = fixup->fixup;
                  tregs->sr = regs->sr;
                  return -1;
            }

            //if (siginfo.si_signo == SIGBUS)
            //    force_sig_info(siginfo.si_signo,
            //                 &siginfo, current);

            /*
             * Oops. The kernel tried to access some bad page. We'll have to
             * terminate things with extreme prejudice.
             */
            if ((unsigned long)siginfo.si_addr < PAGE_SIZE)
                  printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
            else
                  printk(KERN_ALERT "Unable to handle kernel access");
            printk(" at virtual address %p\n", siginfo.si_addr);
            die_if_kernel("Oops", regs, 0 /*error_code*/);
            do_exit(SIGKILL);
      }

      return 1;
}

/*
 * This routine handles page faults.  It determines the problem, and
 * then passes it off to one of the appropriate routines.
 *
 * error_code:
 *    bit 0 == 0 means no page found, 1 means protection fault
 *    bit 1 == 0 means read, 1 means write
 *
 * If this routine detects a bad access, it returns 1, otherwise it
 * returns 0.
 */
int do_page_fault(struct pt_regs *regs, unsigned long address,
                        unsigned long error_code)
{
      struct mm_struct *mm = current->mm;
      struct vm_area_struct * vma;
      int write, fault;

#ifdef DEBUG
      printk ("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
            regs->sr, regs->pc, address, error_code,
            current->mm->pgd);
#endif

      /*
       * If we're in an interrupt or have no user
       * context, we must not take the fault..
       */
      if (in_atomic() || !mm)
            goto no_context;

      down_read(&mm->mmap_sem);

      vma = find_vma(mm, address);
      if (!vma)
            goto map_err;
      if (vma->vm_flags & VM_IO)
            goto acc_err;
      if (vma->vm_start <= address)
            goto good_area;
      if (!(vma->vm_flags & VM_GROWSDOWN))
            goto map_err;
      if (user_mode(regs)) {
            /* Accessing the stack below usp is always a bug.  The
               "+ 256" is there due to some instructions doing
               pre-decrement on the stack and that doesn't show up
               until later.  */
            if (address + 256 < rdusp())
                  goto map_err;
      }
      if (expand_stack(vma, address))
            goto map_err;

/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
#ifdef DEBUG
      printk("do_page_fault: good_area\n");
#endif
      write = 0;
      switch (error_code & 3) {
            default:    /* 3: write, present */
                  /* fall through */
            case 2:           /* write, not present */
                  if (!(vma->vm_flags & VM_WRITE))
                        goto acc_err;
                  write++;
                  break;
            case 1:           /* read, present */
                  goto acc_err;
            case 0:           /* read, not present */
                  if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        goto acc_err;
      }

      /*
       * If for any reason at all we couldn't handle the fault,
       * make sure we exit gracefully rather than endlessly redo
       * the fault.
       */

 survive:
      fault = handle_mm_fault(mm, vma, address, write);
#ifdef DEBUG
      printk("handle_mm_fault returns %d\n",fault);
#endif
      if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM)
                  goto out_of_memory;
            else if (fault & VM_FAULT_SIGBUS)
                  goto bus_err;
            BUG();
      }
      if (fault & VM_FAULT_MAJOR)
            current->maj_flt++;
      else
            current->min_flt++;

      up_read(&mm->mmap_sem);
      return 0;

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
      up_read(&mm->mmap_sem);
      if (is_global_init(current)) {
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }

      printk("VM: killing process %s\n", current->comm);
      if (user_mode(regs))
            do_group_exit(SIGKILL);

no_context:
      current->thread.signo = SIGBUS;
      current->thread.faddr = address;
      return send_fault_sig(regs);

bus_err:
      current->thread.signo = SIGBUS;
      current->thread.code = BUS_ADRERR;
      current->thread.faddr = address;
      goto send_sig;

map_err:
      current->thread.signo = SIGSEGV;
      current->thread.code = SEGV_MAPERR;
      current->thread.faddr = address;
      goto send_sig;

acc_err:
      current->thread.signo = SIGSEGV;
      current->thread.code = SEGV_ACCERR;
      current->thread.faddr = address;

send_sig:
      up_read(&mm->mmap_sem);
      return send_fault_sig(regs);
}

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