gdb/cleanups.c

   1 /* Cleanup routines for GDB, the GNU debugger.
   2
   3    Copyright (C) 1986-2013 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 "gdb_assert.h"
  22
  23 /* The cleanup list records things that have to be undone
  24    if an error happens (descriptors to be closed, memory to be freed, etc.)
  25    Each link in the chain records a function to call and an
  26    argument to give it.
  27
  28    Use make_cleanup to add an element to the cleanup chain.
  29    Use do_cleanups to do all cleanup actions back to a given
  30    point in the chain.  Use discard_cleanups to remove cleanups
  31    from the chain back to a given point, not doing them.
  32
  33    If the argument is pointer to allocated memory, then you need
  34    to additionally set the 'free_arg' member to a function that will
  35    free that memory.  This function will be called both when the cleanup
  36    is executed and when it's discarded.  */
  37
  38 struct cleanup
  39 {
  40   struct cleanup *next;
  41   void (*function) (void *);
  42   void (*free_arg) (void *);
  43   void *arg;
  44 };
  45
  46 /* Used to mark the end of a cleanup chain.
  47    The value is chosen so that it:
  48    - is non-NULL so that make_cleanup never returns NULL,
  49    - causes a segv if dereferenced
  50      [though this won't catch errors that a value of, say,
  51      ((struct cleanup *) -1) will]
  52    - displays as something useful when printed in gdb.
  53    This is const for a bit of extra robustness.
  54    It is initialized to coax gcc into putting it into .rodata.
  55    All fields are initialized to survive -Wextra.  */
  56 static const struct cleanup sentinel_cleanup = { 0, 0, 0, 0 };
  57
  58 /* Handy macro to use when referring to sentinel_cleanup.  */
  59 #define SENTINEL_CLEANUP ((struct cleanup *) &sentinel_cleanup)
  60
  61 /* Chain of cleanup actions established with make_cleanup,
  62    to be executed if an error happens.  */
  63 static struct cleanup *cleanup_chain = SENTINEL_CLEANUP;
  64
  65 /* Chain of cleanup actions established with make_final_cleanup,
  66    to be executed when gdb exits.  */
  67 static struct cleanup *final_cleanup_chain = SENTINEL_CLEANUP;
  68
  69 /* Main worker routine to create a cleanup.
  70    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
  71    FUNCTION is the function to call to perform the cleanup.
  72    ARG is passed to FUNCTION when called.
  73    FREE_ARG, if non-NULL, is called after the cleanup is performed.
  74
  75    The result is a pointer to the previous chain pointer
  76    to be passed later to do_cleanups or discard_cleanups.  */
  77
  78 static struct cleanup *
  79 make_my_cleanup2 (struct cleanup **pmy_chain, make_cleanup_ftype *function,
  80                   void *arg,  void (*free_arg) (void *))
  81 {
  82   struct cleanup *new
  83     = (struct cleanup *) xmalloc (sizeof (struct cleanup));
  84   struct cleanup *old_chain = *pmy_chain;
  85
  86   new->next = *pmy_chain;
  87   new->function = function;
  88   new->free_arg = free_arg;
  89   new->arg = arg;
  90   *pmy_chain = new;
  91
  92   gdb_assert (old_chain != NULL);
  93   return old_chain;
  94 }
  95
  96 /* Worker routine to create a cleanup without a destructor.
  97    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
  98    FUNCTION is the function to call to perform the cleanup.
  99    ARG is passed to FUNCTION when called.
 100
 101    The result is a pointer to the previous chain pointer
 102    to be passed later to do_cleanups or discard_cleanups.  */
 103
 104 static struct cleanup *
 105 make_my_cleanup (struct cleanup **pmy_chain, make_cleanup_ftype *function,
 106                  void *arg)
 107 {
 108   return make_my_cleanup2 (pmy_chain, function, arg, NULL);
 109 }
 110
 111 /* Add a new cleanup to the cleanup_chain,
 112    and return the previous chain pointer
 113    to be passed later to do_cleanups or discard_cleanups.
 114    Args are FUNCTION to clean up with, and ARG to pass to it.  */
 115
 116 struct cleanup *
 117 make_cleanup (make_cleanup_ftype *function, void *arg)
 118 {
 119   return make_my_cleanup (&cleanup_chain, function, arg);
 120 }
 121
 122 /* Same as make_cleanup except also includes TDOR, a destructor to free ARG.
 123    DTOR is invoked when the cleanup is performed or when it is discarded.  */
 124
 125 struct cleanup *
 126 make_cleanup_dtor (make_cleanup_ftype *function, void *arg,
 127                    void (*dtor) (void *))
 128 {
 129   return make_my_cleanup2 (&cleanup_chain,
 130                            function, arg, dtor);
 131 }
 132
 133 /* Same as make_cleanup except the cleanup is added to final_cleanup_chain.  */
 134
 135 struct cleanup *
 136 make_final_cleanup (make_cleanup_ftype *function, void *arg)
 137 {
 138   return make_my_cleanup (&final_cleanup_chain, function, arg);
 139 }
 140
 141 /* Worker routine to perform cleanups.
 142    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
 143    OLD_CHAIN is the result of a "make" cleanup routine.
 144    Cleanups are performed until we get back to the old end of the chain.  */
 145
 146 static void
 147 do_my_cleanups (struct cleanup **pmy_chain,
 148                 struct cleanup *old_chain)
 149 {
 150   struct cleanup *ptr;
 151
 152   while ((ptr = *pmy_chain) != old_chain)
 153     {
 154       *pmy_chain = ptr->next;   /* Do this first in case of recursion.  */
 155       (*ptr->function) (ptr->arg);
 156       if (ptr->free_arg)
 157         (*ptr->free_arg) (ptr->arg);
 158       xfree (ptr);
 159     }
 160 }
 161
 162 /* Return a value that can be passed to do_cleanups, do_final_cleanups to
 163    indicate perform all cleanups.  */
 164
 165 struct cleanup *
 166 all_cleanups (void)
 167 {
 168   return SENTINEL_CLEANUP;
 169 }
 170
 171 /* Discard cleanups and do the actions they describe
 172    until we get back to the point OLD_CHAIN in the cleanup_chain.  */
 173
 174 void
 175 do_cleanups (struct cleanup *old_chain)
 176 {
 177   do_my_cleanups (&cleanup_chain, old_chain);
 178 }
 179
 180 /* Discard cleanups and do the actions they describe
 181    until we get back to the point OLD_CHAIN in the final_cleanup_chain.  */
 182
 183 void
 184 do_final_cleanups (struct cleanup *old_chain)
 185 {
 186   do_my_cleanups (&final_cleanup_chain, old_chain);
 187 }
 188
 189 /* Main worker routine to discard cleanups.
 190    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
 191    OLD_CHAIN is the result of a "make" cleanup routine.
 192    Cleanups are discarded until we get back to the old end of the chain.  */
 193
 194 static void
 195 discard_my_cleanups (struct cleanup **pmy_chain,
 196                      struct cleanup *old_chain)
 197 {
 198   struct cleanup *ptr;
 199
 200   while ((ptr = *pmy_chain) != old_chain)
 201     {
 202       *pmy_chain = ptr->next;
 203       if (ptr->free_arg)
 204         (*ptr->free_arg) (ptr->arg);
 205       xfree (ptr);
 206     }
 207 }
 208
 209 /* Discard cleanups, not doing the actions they describe,
 210    until we get back to the point OLD_CHAIN in the cleanup chain.  */
 211
 212 void
 213 discard_cleanups (struct cleanup *old_chain)
 214 {
 215   discard_my_cleanups (&cleanup_chain, old_chain);
 216 }
 217
 218 /* Discard final cleanups, not doing the actions they describe,
 219    until we get back to the point OLD_CHAIN in the final cleanup chain.  */
 220
 221 void
 222 discard_final_cleanups (struct cleanup *old_chain)
 223 {
 224   discard_my_cleanups (&final_cleanup_chain, old_chain);
 225 }
 226
 227 /* Main worker routine to save cleanups.
 228    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
 229    The chain is emptied and the result is a pointer to the old chain.  */
 230
 231 static struct cleanup *
 232 save_my_cleanups (struct cleanup **pmy_chain)
 233 {
 234   struct cleanup *old_chain = *pmy_chain;
 235
 236   *pmy_chain = SENTINEL_CLEANUP;
 237   return old_chain;
 238 }
 239
 240 /* Set the cleanup_chain to 0, and return the old cleanup_chain.  */
 241
 242 struct cleanup *
 243 save_cleanups (void)
 244 {
 245   return save_my_cleanups (&cleanup_chain);
 246 }
 247
 248 /* Set the final_cleanup_chain to 0, and return the old
 249    final_cleanup_chain.  */
 250
 251 struct cleanup *
 252 save_final_cleanups (void)
 253 {
 254   return save_my_cleanups (&final_cleanup_chain);
 255 }
 256
 257 /* Main worker routine to save cleanups.
 258    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
 259    The chain is restored from CHAIN.  */
 260
 261 static void
 262 restore_my_cleanups (struct cleanup **pmy_chain, struct cleanup *chain)
 263 {
 264   *pmy_chain = chain;
 265 }
 266
 267 /* Restore the cleanup chain from a previously saved chain.  */
 268
 269 void
 270 restore_cleanups (struct cleanup *chain)
 271 {
 272   restore_my_cleanups (&cleanup_chain, chain);
 273 }
 274
 275 /* Restore the final cleanup chain from a previously saved chain.  */
 276
 277 void
 278 restore_final_cleanups (struct cleanup *chain)
 279 {
 280   restore_my_cleanups (&final_cleanup_chain, chain);
 281 }
 282
 283 /* Provide a known function that does nothing, to use as a base for
 284    a possibly long chain of cleanups.  This is useful where we
 285    use the cleanup chain for handling normal cleanups as well as dealing
 286    with cleanups that need to be done as a result of a call to error().
 287    In such cases, we may not be certain where the first cleanup is, unless
 288    we have a do-nothing one to always use as the base.  */
 289
 290 void
 291 null_cleanup (void *arg)
 292 {
 293 }