gdbsupport/cleanups.cc

   1 /* Cleanup routines for GDB, the GNU debugger.
   2
   3    Copyright (C) 1986-2020 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 "common-defs.h"
  21 #include "cleanups.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_final_cleanup,
  62    to be executed when gdb exits.  */
  63 static struct cleanup *final_cleanup_chain = SENTINEL_CLEANUP;
  64
  65 /* Main worker routine to create a cleanup.
  66    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
  67    FUNCTION is the function to call to perform the cleanup.
  68    ARG is passed to FUNCTION when called.
  69    FREE_ARG, if non-NULL, is called after the cleanup is performed.
  70
  71    The result is a pointer to the previous chain pointer
  72    to be passed later to do_cleanups or discard_cleanups.  */
  73
  74 static struct cleanup *
  75 make_my_cleanup2 (struct cleanup **pmy_chain, make_cleanup_ftype *function,
  76                   void *arg,  void (*free_arg) (void *))
  77 {
  78   struct cleanup *newobj = XNEW (struct cleanup);
  79   struct cleanup *old_chain = *pmy_chain;
  80
  81   newobj->next = *pmy_chain;
  82   newobj->function = function;
  83   newobj->free_arg = free_arg;
  84   newobj->arg = arg;
  85   *pmy_chain = newobj;
  86
  87   gdb_assert (old_chain != NULL);
  88   return old_chain;
  89 }
  90
  91 /* Worker routine to create a cleanup without a destructor.
  92    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
  93    FUNCTION is the function to call to perform the cleanup.
  94    ARG is passed to FUNCTION when called.
  95
  96    The result is a pointer to the previous chain pointer
  97    to be passed later to do_cleanups or discard_cleanups.  */
  98
  99 static struct cleanup *
 100 make_my_cleanup (struct cleanup **pmy_chain, make_cleanup_ftype *function,
 101                  void *arg)
 102 {
 103   return make_my_cleanup2 (pmy_chain, function, arg, NULL);
 104 }
 105
 106 /* Add a new cleanup to the final cleanup_chain,
 107    and return the previous chain pointer
 108    to be passed later to do_cleanups or discard_cleanups.
 109    Args are FUNCTION to clean up with, and ARG to pass to it.  */
 110
 111 struct cleanup *
 112 make_final_cleanup (make_cleanup_ftype *function, void *arg)
 113 {
 114   return make_my_cleanup (&final_cleanup_chain, function, arg);
 115 }
 116
 117 /* Worker routine to perform cleanups.
 118    PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
 119    OLD_CHAIN is the result of a "make" cleanup routine.
 120    Cleanups are performed until we get back to the old end of the chain.  */
 121
 122 static void
 123 do_my_cleanups (struct cleanup **pmy_chain,
 124                 struct cleanup *old_chain)
 125 {
 126   struct cleanup *ptr;
 127
 128   while ((ptr = *pmy_chain) != old_chain)
 129     {
 130       *pmy_chain = ptr->next;   /* Do this first in case of recursion.  */
 131       (*ptr->function) (ptr->arg);
 132       if (ptr->free_arg)
 133         (*ptr->free_arg) (ptr->arg);
 134       xfree (ptr);
 135     }
 136 }
 137
 138 /* Discard final cleanups and do the actions they describe.  */
 139
 140 void
 141 do_final_cleanups ()
 142 {
 143   do_my_cleanups (&final_cleanup_chain, SENTINEL_CLEANUP);
 144 }