gdb/mem-break.c

   1 /* Simulate breakpoints by patching locations in the target system, for GDB.
   2    Copyright 1990, 1991, 1995 Free Software Foundation, Inc.
   3    Contributed by Cygnus Support.  Written by John Gilmore.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  20
  21 #include "defs.h"
  22
  23 /* This file is only useful if BREAKPOINT is set.  If not, we punt.  */
  24
  25 #include "symtab.h"
  26 #include "breakpoint.h"
  27 #include "inferior.h"
  28 #include "target.h"
  29
  30
  31 /* Use the program counter to determine the contents and size
  32    of a breakpoint instruction.  If no target-dependent macro
  33    BREAKPOINT_FROM_PC has been defined to implement this function,
  34    assume that the breakpoint doesn't depend on the PC, and
  35    use the values of the BIG_BREAKPOINT and LITTLE_BREAKPOINT macros.
  36    Return a pointer to a string of bytes that encode a breakpoint
  37    instruction, stores the length of the string to *lenptr,
  38    and optionally adjust the pc to point to the correct memory location
  39    for inserting the breakpoint.  */
  40
  41 unsigned char *
  42 memory_breakpoint_from_pc (pcptr, lenptr)
  43      CORE_ADDR *pcptr;
  44      int *lenptr;
  45 {
  46   /* {BIG_,LITTLE_}BREAKPOINT is the sequence of bytes we insert for a
  47      breakpoint.  On some machines, breakpoints are handled by the
  48      target environment and we don't have to worry about them here.  */
  49 #ifdef BIG_BREAKPOINT
  50   if (TARGET_BYTE_ORDER == BIG_ENDIAN)
  51     {
  52       static unsigned char big_break_insn[] = BIG_BREAKPOINT;
  53       *lenptr = sizeof (big_break_insn);
  54       return big_break_insn;
  55     }
  56 #endif
  57 #ifdef LITTLE_BREAKPOINT
  58   if (TARGET_BYTE_ORDER != BIG_ENDIAN)
  59     {
  60       static unsigned char little_break_insn[] = LITTLE_BREAKPOINT;
  61       *lenptr = sizeof (little_break_insn);
  62       return little_break_insn;
  63     }
  64 #endif
  65 #ifdef BREAKPOINT
  66   {
  67     static unsigned char break_insn[] = BREAKPOINT;
  68     *lenptr = sizeof (break_insn);
  69     return break_insn;
  70   }
  71 #endif
  72   *lenptr = 0;
  73   return NULL;
  74 }
  75
  76
  77 /* Insert a breakpoint on targets that don't have any better breakpoint
  78    support.  We read the contents of the target location and stash it,
  79    then overwrite it with a breakpoint instruction.  ADDR is the target
  80    location in the target machine.  CONTENTS_CACHE is a pointer to
  81    memory allocated for saving the target contents.  It is guaranteed
  82    by the caller to be long enough to save BREAKPOINT_LEN bytes (this
  83    is accomplished via BREAKPOINT_MAX).  */
  84
  85 int
  86 memory_insert_breakpoint (addr, contents_cache)
  87      CORE_ADDR addr;
  88      char *contents_cache;
  89 {
  90   int val;
  91   unsigned char *bp;
  92   int bplen;
  93
  94   /* Determine appropriate breakpoint contents and size for this address.  */
  95   bp = BREAKPOINT_FROM_PC (&addr, &bplen);
  96   if (bp == NULL)
  97     error ("Software breakpoints not implemented for this target.");
  98
  99   /* Save the memory contents.  */
 100   val = target_read_memory (addr, contents_cache, bplen);
 101
 102   /* Write the breakpoint.  */
 103   if (val == 0)
 104     val = target_write_memory (addr, (char *)bp, bplen);
 105
 106   return val;
 107 }
 108
 109
 110 int
 111 memory_remove_breakpoint (addr, contents_cache)
 112      CORE_ADDR addr;
 113      char *contents_cache;
 114 {
 115   unsigned char *bp;
 116   int bplen;
 117
 118   /* Determine appropriate breakpoint contents and size for this address.  */
 119   bp = BREAKPOINT_FROM_PC (&addr, &bplen);
 120   if (bp == NULL)
 121     error ("Software breakpoints not implemented for this target.");
 122
 123   return target_write_memory (addr, contents_cache, bplen);
 124 }