gdb/x86-nat.c

   1 /* Native-dependent code for x86 (i386 and x86-64).
   2
   3    Copyright (C) 2001-2017 Free Software Foundation, Inc.
   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 3 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, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "x86-nat.h"
  22 #include "gdbcmd.h"
  23 #include "inferior.h"
  24
  25 /* Support for hardware watchpoints and breakpoints using the x86
  26    debug registers.
  27
  28    This provides several functions for inserting and removing
  29    hardware-assisted breakpoints and watchpoints, testing if one or
  30    more of the watchpoints triggered and at what address, checking
  31    whether a given region can be watched, etc.
  32
  33    The functions below implement debug registers sharing by reference
  34    counts, and allow to watch regions up to 16 bytes long.  */
  35
  36 /* Low-level function vector.  */
  37 struct x86_dr_low_type x86_dr_low;
  38
  39 /* Per-process data.  We don't bind this to a per-inferior registry
  40    because of targets like x86 GNU/Linux that need to keep track of
  41    processes that aren't bound to any inferior (e.g., fork children,
  42    checkpoints).  */
  43
  44 struct x86_process_info
  45 {
  46   /* Linked list.  */
  47   struct x86_process_info *next;
  48
  49   /* The process identifier.  */
  50   pid_t pid;
  51
  52   /* Copy of x86 hardware debug registers.  */
  53   struct x86_debug_reg_state state;
  54 };
  55
  56 static struct x86_process_info *x86_process_list = NULL;
  57
  58 /* Find process data for process PID.  */
  59
  60 static struct x86_process_info *
  61 x86_find_process_pid (pid_t pid)
  62 {
  63   struct x86_process_info *proc;
  64
  65   for (proc = x86_process_list; proc; proc = proc->next)
  66     if (proc->pid == pid)
  67       return proc;
  68
  69   return NULL;
  70 }
  71
  72 /* Add process data for process PID.  Returns newly allocated info
  73    object.  */
  74
  75 static struct x86_process_info *
  76 x86_add_process (pid_t pid)
  77 {
  78   struct x86_process_info *proc = XCNEW (struct x86_process_info);
  79
  80   proc->pid = pid;
  81   proc->next = x86_process_list;
  82   x86_process_list = proc;
  83
  84   return proc;
  85 }
  86
  87 /* Get data specific info for process PID, creating it if necessary.
  88    Never returns NULL.  */
  89
  90 static struct x86_process_info *
  91 x86_process_info_get (pid_t pid)
  92 {
  93   struct x86_process_info *proc;
  94
  95   proc = x86_find_process_pid (pid);
  96   if (proc == NULL)
  97     proc = x86_add_process (pid);
  98
  99   return proc;
 100 }
 101
 102 /* Get debug registers state for process PID.  */
 103
 104 struct x86_debug_reg_state *
 105 x86_debug_reg_state (pid_t pid)
 106 {
 107   return &x86_process_info_get (pid)->state;
 108 }
 109
 110 /* See declaration in x86-nat.h.  */
 111
 112 void
 113 x86_forget_process (pid_t pid)
 114 {
 115   struct x86_process_info *proc, **proc_link;
 116
 117   proc = x86_process_list;
 118   proc_link = &x86_process_list;
 119
 120   while (proc != NULL)
 121     {
 122       if (proc->pid == pid)
 123         {
 124           *proc_link = proc->next;
 125
 126           xfree (proc);
 127           return;
 128         }
 129
 130       proc_link = &proc->next;
 131       proc = *proc_link;
 132     }
 133 }
 134
 135 /* Clear the reference counts and forget everything we knew about the
 136    debug registers.  */
 137
 138 void
 139 x86_cleanup_dregs (void)
 140 {
 141   /* Starting from scratch has the same effect.  */
 142   x86_forget_process (ptid_get_pid (inferior_ptid));
 143 }
 144
 145 /* Insert a watchpoint to watch a memory region which starts at
 146    address ADDR and whose length is LEN bytes.  Watch memory accesses
 147    of the type TYPE.  Return 0 on success, -1 on failure.  */
 148
 149 static int
 150 x86_insert_watchpoint (struct target_ops *self, CORE_ADDR addr, int len,
 151                        enum target_hw_bp_type type, struct expression *cond)
 152 {
 153   struct x86_debug_reg_state *state
 154     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 155
 156   return x86_dr_insert_watchpoint (state, type, addr, len);
 157 }
 158
 159 /* Remove a watchpoint that watched the memory region which starts at
 160    address ADDR, whose length is LEN bytes, and for accesses of the
 161    type TYPE.  Return 0 on success, -1 on failure.  */
 162 static int
 163 x86_remove_watchpoint (struct target_ops *self, CORE_ADDR addr, int len,
 164                        enum target_hw_bp_type type, struct expression *cond)
 165 {
 166   struct x86_debug_reg_state *state
 167     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 168
 169   return x86_dr_remove_watchpoint (state, type, addr, len);
 170 }
 171
 172 /* Return non-zero if we can watch a memory region that starts at
 173    address ADDR and whose length is LEN bytes.  */
 174
 175 static int
 176 x86_region_ok_for_watchpoint (struct target_ops *self,
 177                               CORE_ADDR addr, int len)
 178 {
 179   struct x86_debug_reg_state *state
 180     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 181
 182   return x86_dr_region_ok_for_watchpoint (state, addr, len);
 183 }
 184
 185 /* If the inferior has some break/watchpoint that triggered, set the
 186    address associated with that break/watchpoint and return non-zero.
 187    Otherwise, return zero.  */
 188
 189 static int
 190 x86_stopped_data_address (struct target_ops *ops, CORE_ADDR *addr_p)
 191 {
 192   struct x86_debug_reg_state *state
 193     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 194
 195   return x86_dr_stopped_data_address (state, addr_p);
 196 }
 197
 198 /* Return non-zero if the inferior has some watchpoint that triggered.
 199    Otherwise return zero.  */
 200
 201 static int
 202 x86_stopped_by_watchpoint (struct target_ops *ops)
 203 {
 204   struct x86_debug_reg_state *state
 205     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 206
 207   return x86_dr_stopped_by_watchpoint (state);
 208 }
 209
 210 /* Insert a hardware-assisted breakpoint at BP_TGT->reqstd_address.
 211    Return 0 on success, EBUSY on failure.  */
 212
 213 static int
 214 x86_insert_hw_breakpoint (struct target_ops *self, struct gdbarch *gdbarch,
 215                           struct bp_target_info *bp_tgt)
 216 {
 217   struct x86_debug_reg_state *state
 218     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 219
 220   bp_tgt->placed_address = bp_tgt->reqstd_address;
 221   return x86_dr_insert_watchpoint (state, hw_execute,
 222                                    bp_tgt->placed_address, 1) ? EBUSY : 0;
 223 }
 224
 225 /* Remove a hardware-assisted breakpoint at BP_TGT->placed_address.
 226    Return 0 on success, -1 on failure.  */
 227
 228 static int
 229 x86_remove_hw_breakpoint (struct target_ops *self, struct gdbarch *gdbarch,
 230                           struct bp_target_info *bp_tgt)
 231 {
 232   struct x86_debug_reg_state *state
 233     = x86_debug_reg_state (ptid_get_pid (inferior_ptid));
 234
 235   return x86_dr_remove_watchpoint (state, hw_execute,
 236                                    bp_tgt->placed_address, 1);
 237 }
 238
 239 /* Returns the number of hardware watchpoints of type TYPE that we can
 240    set.  Value is positive if we can set CNT watchpoints, zero if
 241    setting watchpoints of type TYPE is not supported, and negative if
 242    CNT is more than the maximum number of watchpoints of type TYPE
 243    that we can support.  TYPE is one of bp_hardware_watchpoint,
 244    bp_read_watchpoint, bp_write_watchpoint, or bp_hardware_breakpoint.
 245    CNT is the number of such watchpoints used so far (including this
 246    one).  OTHERTYPE is non-zero if other types of watchpoints are
 247    currently enabled.
 248
 249    We always return 1 here because we don't have enough information
 250    about possible overlap of addresses that they want to watch.  As an
 251    extreme example, consider the case where all the watchpoints watch
 252    the same address and the same region length: then we can handle a
 253    virtually unlimited number of watchpoints, due to debug register
 254    sharing implemented via reference counts in x86-nat.c.  */
 255
 256 static int
 257 x86_can_use_hw_breakpoint (struct target_ops *self,
 258                            enum bptype type, int cnt, int othertype)
 259 {
 260   return 1;
 261 }
 262
 263 static void
 264 add_show_debug_regs_command (void)
 265 {
 266   /* A maintenance command to enable printing the internal DRi mirror
 267      variables.  */
 268   add_setshow_boolean_cmd ("show-debug-regs", class_maintenance,
 269                            &show_debug_regs, _("\
 270 Set whether to show variables that mirror the x86 debug registers."), _("\
 271 Show whether to show variables that mirror the x86 debug registers."), _("\
 272 Use \"on\" to enable, \"off\" to disable.\n\
 273 If enabled, the debug registers values are shown when GDB inserts\n\
 274 or removes a hardware breakpoint or watchpoint, and when the inferior\n\
 275 triggers a breakpoint or watchpoint."),
 276                            NULL,
 277                            NULL,
 278                            &maintenance_set_cmdlist,
 279                            &maintenance_show_cmdlist);
 280 }
 281
 282 /* There are only two global functions left.  */
 283
 284 void
 285 x86_use_watchpoints (struct target_ops *t)
 286 {
 287   /* After a watchpoint trap, the PC points to the instruction after the
 288      one that caused the trap.  Therefore we don't need to step over it.
 289      But we do need to reset the status register to avoid another trap.  */
 290   t->to_have_continuable_watchpoint = 1;
 291
 292   t->to_can_use_hw_breakpoint = x86_can_use_hw_breakpoint;
 293   t->to_region_ok_for_hw_watchpoint = x86_region_ok_for_watchpoint;
 294   t->to_stopped_by_watchpoint = x86_stopped_by_watchpoint;
 295   t->to_stopped_data_address = x86_stopped_data_address;
 296   t->to_insert_watchpoint = x86_insert_watchpoint;
 297   t->to_remove_watchpoint = x86_remove_watchpoint;
 298   t->to_insert_hw_breakpoint = x86_insert_hw_breakpoint;
 299   t->to_remove_hw_breakpoint = x86_remove_hw_breakpoint;
 300 }
 301
 302 void
 303 x86_set_debug_register_length (int len)
 304 {
 305   /* This function should be called only once for each native target.  */
 306   gdb_assert (x86_dr_low.debug_register_length == 0);
 307   gdb_assert (len == 4 || len == 8);
 308   x86_dr_low.debug_register_length = len;
 309   add_show_debug_regs_command ();
 310 }