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I am sending this as an RFC because it's far from complete and definitive, but I'd like to gather some comments and opinions before going further in this direction. The goal of this patch is to decouple the notion of the user-selected inferior/thread/frame from GDB's internally selected inferior/thread/frame. Currently, for example, the inferior_ptid variable has two jobs: - it's the user-selected thread: it's changed by the "thread" command. Other commands (continue, backtrace, etc) apply to this thread. - it's the internally-selected thread: it defines the thread GDB is currently "working" on. For example, implementations of to_xfer_partial will refer to it to know from which thread to read/write memory. Because of this dual usage, if we want to do some operations on a thread other than the currently selected one, we have to save the current inferior/thread/frame and restore them when we're done. Failing to do so would result in an unexpected selection switch for the user. To improve this, Pedro suggested in [1] to decouple the two concepts. This is essentially what this patch is trying to do. A new "user_selection" object is introduced, which contains the selected inferior/thread/frame from the point of view of the user. Before every command, we "apply" this selection to the core of GDB to make sure the internal selection matches the user selection. There is a single user selection for the whole GDB (named "global user-selection"), but as was mentioned in the linked thread, it opens the door to having different selections for different UIs. This means that each UI would have its own user-selection object, which would be applied to the core prior to executing commands from this UI. The global user-selection object only gets modified when we really intend to change it. It can be because of the thread / -thread-select / up / down / frame / inferior commands, a breakpoint hit in all-stop, an inferior exit, etc. The problem that initially prompted this effort is that the "--thread" flag of MI commands changes the user-selected thread under the user's feet. My initial attempt to fix it was to restore the selection after the MI command execution. However, some cases are hard to get right. For example: (thread 1 is currently selected) -interpreter-exec --thread 2 console "thread 3" Restoring the selected thread to thread 1 after the MI command execution wrongfully cancels the switch to thread 3. So it's hard to determine when we should or shouldn't restore. With the current patch, it works naturally: the --thread flag doesn't touch the user-selected thread, only the internal one. The "thread 3" command updates the user selection. Another difficulty is to send the right notifications to MI when the user selection changes. That means to not miss any, but not send too many either. Getting it somewhat right lead to ugly hacks (see the command_notifies_uscc_observer function) and even then it's not perfect (see the kfails in user-selected-context-sync.exp test). With the proposed method, it's easy to know when the user-selection changes and send notifications. With this patch, there are probably a few usage of make_cleanup_restore_current_thread that are not needed anymore, if they are only used to restore the user selection. I kept removing them for a later time though. In the current state, there are a few minor regressions in the testsuite (especially some follow-fork stuff I'm not sure how to handle), but the vast majority of the previously passing tests still pass. Comments are welcome! Thanks, Simon [1] https://sourceware.org/ml/gdb-patches/2016-08/msg00031.html
55 lines
1.9 KiB
C
55 lines
1.9 KiB
C
/* Library interface into GDB.
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Copyright (C) 1999-2017 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef GDB_H
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#define GDB_H
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struct ui_out;
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/* Return-code (RC) from a gdb library call. (The abreviation RC is
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taken from the sim/common directory.) */
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enum gdb_rc {
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/* The operation failed. The failure message can be fetched by
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calling ``char *error_last_message(void)''. The value is
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determined by the catch_errors() interface. The MSG parameter is
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set to a freshly allocated copy of the error message. */
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/* NOTE: Since ``defs.h:catch_errors()'' does not return an error /
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internal / quit indication it is not possible to return that
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here. */
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GDB_RC_FAIL = 0,
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/* No error occured but nothing happened. Due to the catch_errors()
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interface, this must be non-zero. */
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GDB_RC_NONE = 1,
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/* The operation was successful. Due to the catch_errors()
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interface, this must be non-zero. */
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GDB_RC_OK = 2
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};
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/* Print the specified breakpoint on GDB_STDOUT. (Eventually this
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function will ``print'' the object on ``output''). */
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enum gdb_rc gdb_breakpoint_query (struct ui_out *uiout, int bnum,
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char **error_message);
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/* Print a list of known thread ids. */
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enum gdb_rc gdb_list_thread_ids (struct ui_out *uiout,
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char **error_message);
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#endif
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