gdbsupport/cleanups.cc

/* Cleanup routines for GDB, the GNU debugger.

   Copyright (C) 1986-2021 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "common-defs.h"
#include "cleanups.h"

/* The cleanup list records things that have to be undone
   if an error happens (descriptors to be closed, memory to be freed, etc.)
   Each link in the chain records a function to call and an
   argument to give it.

   Use make_cleanup to add an element to the cleanup chain.
   Use do_cleanups to do all cleanup actions back to a given
   point in the chain.  Use discard_cleanups to remove cleanups
   from the chain back to a given point, not doing them.

   If the argument is pointer to allocated memory, then you need
   to additionally set the 'free_arg' member to a function that will
   free that memory.  This function will be called both when the cleanup
   is executed and when it's discarded.  */

struct cleanup
{
  struct cleanup *next;
  void (*function) (void *);
  void (*free_arg) (void *);
  void *arg;
};

/* Used to mark the end of a cleanup chain.
   The value is chosen so that it:
   - is non-NULL so that make_cleanup never returns NULL,
   - causes a segv if dereferenced
     [though this won't catch errors that a value of, say,
     ((struct cleanup *) -1) will]
   - displays as something useful when printed in gdb.
   This is const for a bit of extra robustness.
   It is initialized to coax gcc into putting it into .rodata.
   All fields are initialized to survive -Wextra.  */
static const struct cleanup sentinel_cleanup = { 0, 0, 0, 0 };

/* Handy macro to use when referring to sentinel_cleanup.  */
#define SENTINEL_CLEANUP ((struct cleanup *) &sentinel_cleanup)

/* Chain of cleanup actions established with make_final_cleanup,
   to be executed when gdb exits.  */
static struct cleanup *final_cleanup_chain = SENTINEL_CLEANUP;

/* Main worker routine to create a cleanup.
   PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
   FUNCTION is the function to call to perform the cleanup.
   ARG is passed to FUNCTION when called.
   FREE_ARG, if non-NULL, is called after the cleanup is performed.

   The result is a pointer to the previous chain pointer
   to be passed later to do_cleanups or discard_cleanups.  */

static struct cleanup *
make_my_cleanup2 (struct cleanup **pmy_chain, make_cleanup_ftype *function,
		  void *arg,  void (*free_arg) (void *))
{
  struct cleanup *newobj = XNEW (struct cleanup);
  struct cleanup *old_chain = *pmy_chain;

  newobj->next = *pmy_chain;
  newobj->function = function;
  newobj->free_arg = free_arg;
  newobj->arg = arg;
  *pmy_chain = newobj;

  gdb_assert (old_chain != NULL);
  return old_chain;
}

/* Worker routine to create a cleanup without a destructor.
   PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
   FUNCTION is the function to call to perform the cleanup.
   ARG is passed to FUNCTION when called.

   The result is a pointer to the previous chain pointer
   to be passed later to do_cleanups or discard_cleanups.  */

static struct cleanup *
make_my_cleanup (struct cleanup **pmy_chain, make_cleanup_ftype *function,
		 void *arg)
{
  return make_my_cleanup2 (pmy_chain, function, arg, NULL);
}

/* Add a new cleanup to the final cleanup_chain,
   and return the previous chain pointer
   to be passed later to do_cleanups or discard_cleanups.
   Args are FUNCTION to clean up with, and ARG to pass to it.  */

struct cleanup *
make_final_cleanup (make_cleanup_ftype *function, void *arg)
{
  return make_my_cleanup (&final_cleanup_chain, function, arg);
}

/* Worker routine to perform cleanups.
   PMY_CHAIN is a pointer to either cleanup_chain or final_cleanup_chain.
   OLD_CHAIN is the result of a "make" cleanup routine.
   Cleanups are performed until we get back to the old end of the chain.  */

static void
do_my_cleanups (struct cleanup **pmy_chain,
		struct cleanup *old_chain)
{
  struct cleanup *ptr;

  while ((ptr = *pmy_chain) != old_chain)
    {
      *pmy_chain = ptr->next;	/* Do this first in case of recursion.  */
      (*ptr->function) (ptr->arg);
      if (ptr->free_arg)
	(*ptr->free_arg) (ptr->arg);
      xfree (ptr);
    }
}

/* Discard final cleanups and do the actions they describe.  */

void
do_final_cleanups ()
{
  do_my_cleanups (&final_cleanup_chain, SENTINEL_CLEANUP);
}