usercopy.c

linux内核源码

/*
 * User address space access functions.
 * The non-inlined parts of asm-cris/uaccess.h are here.
 *
 * Copyright (C) 2000, Axis Communications AB.
 *
 * Written by Hans-Peter Nilsson.
 * Pieces used from memcpy, originally by Kenny Ranerup long time ago.
 */

#include <asm/uaccess.h>

/* Asm:s have been tweaked (within the domain of correctness) to give
   satisfactory results for "gcc version 2.96 20000427 (experimental)".

   Check regularly...

   Note that the PC saved at a bus-fault is the address *after* the
   faulting instruction, which means the branch-target for instructions in
   delay-slots for taken branches.  Note also that the postincrement in
   the instruction is performed regardless of bus-fault; the register is
   seen updated in fault handlers.

   Oh, and on the code formatting issue, to whomever feels like "fixing
   it" to Conformity: I'm too "lazy", but why don't you go ahead and "fix"
   string.c too.  I just don't think too many people will hack this file
   for the code format to be an issue.  */


/* Copy to userspace.  This is based on the memcpy used for
   kernel-to-kernel copying; see "string.c".  */

unsigned long
__copy_user (void __user *pdst, const void *psrc, unsigned long pn)
{
  /* We want the parameters put in special registers.
     Make sure the compiler is able to make something useful of this.
     As it is now: r10 -> r13; r11 -> r11 (nop); r12 -> r12 (nop).

     FIXME: Comment for old gcc version.  Check.
     If gcc was alright, it really would need no temporaries, and no
     stack space to save stuff on. */

  register char *dst __asm__ ("r13") = pdst;
  register const char *src __asm__ ("r11") = psrc;
  register int n __asm__ ("r12") = pn;
  register int retn __asm__ ("r10") = 0;


  /* When src is aligned but not dst, this makes a few extra needless
     cycles.  I believe it would take as many to check that the
     re-alignment was unnecessary.  */
  if (((unsigned long) dst & 3) != 0
      /* Don't align if we wouldn't copy more than a few bytes; so we
	 don't have to check further for overflows.  */
      && n >= 3)
  {
    if ((unsigned long) dst & 1)
    {
      __asm_copy_to_user_1 (dst, src, retn);
      n--;
    }

    if ((unsigned long) dst & 2)
    {
      __asm_copy_to_user_2 (dst, src, retn);
      n -= 2;
    }
  }

  /* Decide which copying method to use. */
  if (n >= 44*2)		/* Break even between movem and
				   move16 is at 38.7*2, but modulo 44. */
  {
    /* For large copies we use 'movem'.  */

    /* It is not optimal to tell the compiler about clobbering any
       registers; that will move the saving/restoring of those registers
       to the function prologue/epilogue, and make non-movem sizes
       suboptimal.

       This method is not foolproof; it assumes that the "asm reg"
       declarations at the beginning of the function really are used
       here (beware: they may be moved to temporary registers).
       This way, we do not have to save/move the registers around into
       temporaries; we can safely use them straight away.

       If you want to check that the allocation was right; then
       check the equalities in the first comment.  It should say
       "r13=r13, r11=r11, r12=r12".  */
    __asm__ volatile ("\
	.ifnc %0%1%2%3,$r13$r11$r12$r10					\n\
	.err								\n\
	.endif								\n\
									\n\
	;; Save the registers we'll use in the movem process		\n\
	;; on the stack.						\n\
	subq	11*4,$sp						\n\
	movem	$r10,[$sp]						\n\
									\n\
	;; Now we've got this:						\n\
	;; r11 - src							\n\
	;; r13 - dst							\n\
	;; r12 - n							\n\
									\n\
	;; Update n for the first loop					\n\
	subq	44,$r12							\n\
									\n\
; Since the noted PC of a faulting instruction in a delay-slot of a taken \n\
; branch, is that of the branch target, we actually point at the from-movem \n\
; for this case.  There is no ambiguity here; if there was a fault in that \n\
; instruction (meaning a kernel oops), the faulted PC would be the address \n\
; after *that* movem.							\n\
									\n\
0:									\n\
	movem	[$r11+],$r10						\n\
	subq   44,$r12							\n\
	bge	0b							\n\
	movem	$r10,[$r13+]						\n\
1:									\n\
	addq   44,$r12  ;; compensate for last loop underflowing n	\n\
									\n\
	;; Restore registers from stack					\n\
	movem [$sp+],$r10						\n\
2:									\n\
	.section .fixup,\"ax\"						\n\
									\n\
; To provide a correct count in r10 of bytes that failed to be copied,	\n\
; we jump back into the loop if the loop-branch was taken.  There is no	\n\
; performance penalty for sany use; the program will segfault soon enough.\n\
									\n\
3:									\n\
	move.d [$sp],$r10						\n\
	addq 44,$r10							\n\
	move.d $r10,[$sp]						\n\
	jump 0b								\n\
4:									\n\
	movem [$sp+],$r10						\n\
	addq 44,$r10							\n\
	addq 44,$r12							\n\
	jump 2b								\n\
									\n\
	.previous							\n\
	.section __ex_table,\"a\"					\n\
	.dword 0b,3b							\n\
	.dword 1b,4b							\n\
	.previous"

     /* Outputs */ : "=r" (dst), "=r" (src), "=r" (n), "=r" (retn)
     /* Inputs */ : "0" (dst), "1" (src), "2" (n), "3" (retn));

  }

  /* Either we directly start copying, using dword copying in a loop, or
     we copy as much as possible with 'movem' and then the last block (<44
     bytes) is copied here.  This will work since 'movem' will have
     updated SRC, DST and N.  */

  while (n >= 16)
  {
    __asm_copy_to_user_16 (dst, src, retn);
    n -= 16;
  }

  /* Having a separate by-four loops cuts down on cache footprint.
     FIXME:  Test with and without; increasing switch to be 0..15.  */
  while (n >= 4)
  {
    __asm_copy_to_user_4 (dst, src, retn);
    n -= 4;
  }

  switch (n)
  {
    case 0:
      break;
    case 1:
      __asm_copy_to_user_1 (dst, src, retn);
      break;
    case 2:
      __asm_copy_to_user_2 (dst, src, retn);
      break;
    case 3:
      __asm_copy_to_user_3 (dst, src, retn);
      break;
  }

  return retn;
}

/* Copy from user to kernel, zeroing the bytes that were inaccessible in
   userland.  The return-value is the number of bytes that were
   inaccessible.  */

unsigned long
__copy_user_zeroing (void __user *pdst, const void *psrc, unsigned long pn)
{
  /* We want the parameters put in special registers.
     Make sure the compiler is able to make something useful of this.
     As it is now: r10 -> r13; r11 -> r11 (nop); r12 -> r12 (nop).

     FIXME: Comment for old gcc version.  Check.
     If gcc was alright, it really would need no temporaries, and no
     stack space to save stuff on.  */

  register char *dst __asm__ ("r13") = pdst;
  register const char *src __asm__ ("r11") = psrc;
  register int n __asm__ ("r12") = pn;
  register int retn __asm__ ("r10") = 0;

  /* The best reason to align src is that we then know that a read-fault
     was for aligned bytes; there's no 1..3 remaining good bytes to
     pickle.  */
  if (((unsigned long) src & 3) != 0)
  {
    if (((unsigned long) src & 1) && n != 0)
    {
      __asm_copy_from_user_1 (dst, src, retn);
      n--;
    }

    if (((unsigned long) src & 2) && n >= 2)
    {
      __asm_copy_from_user_2 (dst, src, retn);
      n -= 2;
    }

    /* We only need one check after the unalignment-adjustments, because
       if both adjustments were done, either both or neither reference
       had an exception.  */
    if (retn != 0)
      goto copy_exception_bytes;
  }

  /* Decide which copying method to use. */
  if (n >= 44*2)		/* Break even between movem and
				   move16 is at 38.7*2, but modulo 44.
				   FIXME: We use move4 now.  */
  {
    /* For large copies we use 'movem' */

    /* It is not optimal to tell the compiler about clobbering any
       registers; that will move the saving/restoring of those registers
       to the function prologue/epilogue, and make non-movem sizes
       suboptimal.

       This method is not foolproof; it assumes that the "asm reg"
       declarations at the beginning of the function really are used
       here (beware: they may be moved to temporary registers).
       This way, we do not have to save/move the registers around into
       temporaries; we can safely use them straight away.

       If you want to check that the allocation was right; then
       check the equalities in the first comment.  It should say
       "r13=r13, r11=r11, r12=r12" */
    __asm__ volatile ("\n\
	.ifnc %0%1%2%3,$r13$r11$r12$r10					\n\
	.err								\n\
	.endif								\n\
									\n\
	;; Save the registers we'll use in the movem process		\n\
	;; on the stack.						\n\