binutils-gdb/gdb/common/refcounted-object.h

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Fix removing inferiors from within "thread apply" commands This patch fixes an internal error exposed by a test that does something like: define kill-and-remove kill inferiors 2 remove-inferiors 2 end # Start one inferior. start # Start another inferior. add-inferior 2 inferior 2 start # Kill and remove inferior 1 while inferior 2 is selected. thread apply 1.1 kill-and-remove The internal error looks like this: Thread 1.1 (Thread 0x7ffff7fc2700 (LWP 20677)): [Switching to inferior 1 [process 20677] (gdb/testsuite/outputs/gdb.threads/threadapply/threadapply)] [Switching to thread 1.1 (Thread 0x7ffff7fc2700 (LWP 20677))] #0 main () at src/gdb/testsuite/gdb.threads/threadapply.c:38 38 for (i = 0; i < NUM; i++) src/gdb/inferior.c:66: internal-error: void set_current_inferior(inferior*): Assertion `inf != NULL' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. Quit this debugging session? (y or n) FAIL: gdb.threads/threadapply.exp: kill_and_remove_inferior: try kill-and-remove: thread apply 1.1 kill-and-remove (GDB internal error) There are several problems around this area of the code. One is that in do_restore_current_thread_cleanup, we do a look up of inferior by ptid, which can find the wrong inferior if the previously selected inferior exited and some other inferior was started with a reused pid (rare, but still...). The other problem is that the "remove-inferiors" command rejects attempts to remove the current inferior, but when we get to "remove-inferiors" in a "thread apply THR remove-inferiors 2" command, the current inferior is the inferior of thread THR, not the previously selected inferior, so if the previously selected inferior was inferior 2, that command still manages to wipe it, and then gdb restores the old selected inferior, which is now a dangling pointer... So the fix here is: - Make make_cleanup_restore_current_thread store a pointer to the previously selected inferior directly, and use it directly instead of doing ptid look ups. - Add a refcount to inferiors, very similar to thread_info's refcount, that is incremented/decremented by make_cleanup_restore_current_thread, and checked before deleting an inferior. To avoid duplication, a new refcounted_object type is added, that both thread_info and inferior inherit from. gdb/ChangeLog: 2017-04-19 Pedro Alves <palves@redhat.com> * common/refcounted-object.h: New file. * gdbthread.h: Include "common/refcounted-object.h". (thread_info): Inherit from refcounted_object and add comments. (thread_info::incref, thread_info::decref) (thread_info::m_refcount): Delete. (thread_info::deletable): Use the refcounted_object::refcount() method. * inferior.c (current_inferior_): Add comment. (set_current_inferior): Increment/decrement refcounts. (prune_inferiors, remove_inferior_command): Skip inferiors marked not-deletable instead of comparing with the current inferior. (initialize_inferiors): Increment the initial inferior's refcount. * inferior.h (struct inferior): Forward declare. Include "common/refcounted-object.h". (current_inferior, set_current_inferior): Move declaration to before struct inferior's definition, and fix comment. (inferior): Inherit from refcounted_object. Add comments. * thread.c (switch_to_thread_no_regs): Reference the thread's inferior pointer directly instead of doing a ptid lookup. (switch_to_no_thread): New function. (switch_to_thread(thread_info *)): New function, factored out from ... (switch_to_thread(ptid_t)): ... this. (restore_current_thread): Delete. (current_thread_cleanup): Remove 'inf_id' and 'was_removable' fields, and add 'inf' field. (do_restore_current_thread_cleanup): Check whether old->inf is alive instead of looking up an inferior by ptid. Use switch_to_thread and switch_to_no_thread. (restore_current_thread_cleanup_dtor): Use old->inf directly instead of lookup up an inferior by id. Decref the inferior. Don't restore 'removable'. (make_cleanup_restore_current_thread): Same the inferior pointer in old, instead of the inferior number. Incref the inferior. Don't save/clear 'removable'. gdb/testsuite/ChangeLog: 2017-04-19 Pedro Alves <palves@redhat.com> * gdb.threads/threadapply.exp (kill_and_remove_inferior): New procedure. (top level): Call it. * lib/gdb.exp (gdb_define_cmd): New procedure.
2017-04-19 20:12:23 +08:00
/* Base class of intrusively reference-counted objects.
Copyright (C) 2017 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/>. */
#ifndef REFCOUNTED_OBJECT_H
#define REFCOUNTED_OBJECT_H
/* Base class of intrusively reference-countable objects.
Incrementing and decrementing the reference count is an external
responsibility. */
class refcounted_object
{
public:
refcounted_object () = default;
/* Increase the refcount. */
void incref ()
{
gdb_assert (m_refcount >= 0);
m_refcount++;
}
/* Decrease the refcount. */
void decref ()
{
m_refcount--;
gdb_assert (m_refcount >= 0);
}
int refcount () const { return m_refcount; }
private:
/* Disable copy. */
refcounted_object (const refcounted_object &) = delete;
refcounted_object &operator=(const refcounted_object &) = delete;
/* The reference count. */
int m_refcount = 0;
};
#endif /* REFCOUNTED_OBJECT_H */