[PATCH v2 1/1] gdb/mi: PR20684, preserve user selected thread and frame when invoking MI commands

[Jan Vrany <jan.vrany@labware.com>]

When invoking MI commands with --thread and/or --frame, user selected
thread and frame was not preserved:

  (gdb)
  info thread
  &"info thread\n"
  ~"  Id   Target Id                                           Frame \n"
  ~"* 1    Thread 0x7ffff7c30740 (LWP 19302) \"user-selected-c\" main () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60\n"
  ~"  2    Thread 0x7ffff7c2f700 (LWP 19306) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ~"  3    Thread 0x7ffff742e700 (LWP 19307) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ^done
  (gdb)
  info frame
  &"info frame\n"
  ~"Stack level 0, frame at 0x7fffffffdf90:\n"
  ~" rip = 0x555555555207 in main (/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60); saved rip = 0x7ffff7c5709b\n"
  ~" source language c.\n"
  ~" Arglist at 0x7fffffffdf80, args: \n"
  ~" Locals at 0x7fffffffdf80, Previous frame's sp is 0x7fffffffdf90\n"
  ~" Saved registers:\n "
  ~" rbp at 0x7fffffffdf80, rip at 0x7fffffffdf88\n"
  ^done
  (gdb)
  -stack-info-depth --thread 3
  ^done,depth="4"
  (gdb)
  info thread
  &"info thread\n"
  ~"  Id   Target Id                                           Frame \n"
  ~"  1    Thread 0x7ffff7c30740 (LWP 19302) \"user-selected-c\" main () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60\n"
  ~"  2    Thread 0x7ffff7c2f700 (LWP 19306) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ~"* 3    Thread 0x7ffff742e700 (LWP 19307) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ^done
  (gdb)
  info frame
  &"info frame\n"
  ~"Stack level 0, frame at 0x7ffff742dee0:\n"
  ~" rip = 0x555555555169 in child_sub_function (/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30); saved rip = 0x555555555188\n"
  ~" called by frame at 0x7ffff742df00\n"
  ~" source language c.\n"
  ~" Arglist at 0x7ffff742ded0, args: \n"
  ~" Locals at 0x7ffff742ded0, Previous frame's sp is 0x7ffff742dee0\n"
  ~" Saved registers:\n "
  ~" rbp at 0x7ffff742ded0, rip at 0x7ffff742ded8\n"
  ^done
  (gdb)

This was problematic for frontends that provide access to CLI because UI
may silently change the context for CLI commands (as demonstrated above).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=20684
---
 gdb/mi/mi-cmds.h                             |  12 ++
 gdb/mi/mi-main.c                             |  13 +-
 gdb/testsuite/gdb.mi/mi-cmd-user-context.exp | 155 +++++++++++++++++++
 3 files changed, 178 insertions(+), 2 deletions(-)
 create mode 100644 gdb/testsuite/gdb.mi/mi-cmd-user-context.exp

diff --git a/gdb/mi/mi-cmds.h b/gdb/mi/mi-cmds.h
index 2a93a9f5476..785652ee1c9 100644
--- a/gdb/mi/mi-cmds.h
+++ b/gdb/mi/mi-cmds.h
@@ -23,6 +23,7 @@
 #define MI_MI_CMDS_H
 
 #include "gdbsupport/gdb_optional.h"
+#include "mi/mi-main.h"
 
 enum print_values {
    PRINT_NO_VALUES,
@@ -163,6 +164,17 @@ struct mi_command
      wrong.  */
   void invoke (struct mi_parse *parse) const;
 
+  /* Return whether this command preserves user selected context (thread
+     and frame).  */
+  bool preserve_user_selected_context () const
+  {
+    /* Here we exploit the fact that if MI command is supposed to change
+       user context, then it should not emit change notifications.  Therefore if
+       command does not suppress user context change notifications, then it should
+       preserve the context.  */
+    return m_suppress_notification != &mi_suppress_notification.user_selected_context;
+  }
+
 protected:
 
   /* The core of command invocation, this needs to be overridden in each
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 4860da7536a..b25e87a1476 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -2037,6 +2037,7 @@ mi_cmd_execute (struct mi_parse *parse)
       set_current_program_space (inf->pspace);
     }
 
+  gdb::optional<scoped_restore_current_thread> thread_saver;
   if (parse->thread != -1)
     {
       thread_info *tp = find_thread_global_id (parse->thread);
@@ -2047,9 +2048,13 @@ mi_cmd_execute (struct mi_parse *parse)
       if (tp->state == THREAD_EXITED)
 	error (_("Thread id: %d has terminated"), parse->thread);
 
+      if (parse->cmd->preserve_user_selected_context ())
+	thread_saver.emplace ();
+
       switch_to_thread (tp);
     }
 
+  gdb::optional<scoped_restore_selected_frame> frame_saver;
   if (parse->frame != -1)
     {
       struct frame_info *fid;
@@ -2057,8 +2062,12 @@ mi_cmd_execute (struct mi_parse *parse)
 
       fid = find_relative_frame (get_current_frame (), &frame);
       if (frame == 0)
-	/* find_relative_frame was successful */
-	select_frame (fid);
+        {
+	  if (parse->cmd->preserve_user_selected_context ())
+	    frame_saver.emplace ();
+
+          select_frame (fid);
+        }
       else
 	error (_("Invalid frame id: %d"), frame);
     }
diff --git a/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp b/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp
new file mode 100644
index 00000000000..a373dd3a4b0
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp
@@ -0,0 +1,155 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test that GDB/MI commands preserve user selected context when
+# passed --thread and/or --frame.
+
+load_lib mi-support.exp
+
+standard_testfile user-selected-context-sync.c
+
+if {[build_executable $testfile.exp $testfile ${srcfile} "debug pthreads"] == -1} {
+    untested "failed to compile"
+    return -1
+}
+
+set main_break_line [gdb_get_line_number "main break line"]
+
+set any "\[^\r\n\]*"
+set nl  "\[\r\n\]"
+
+mi_clean_restart $binfile
+mi_create_breakpoint "$srcfile:$main_break_line" "set breakpoint in main"
+mi_run_cmd
+mi_expect_stop "breakpoint-hit" "main" "" $srcfile $main_break_line \
+	 { "" "disp=\"keep\"" } "run to breakpoint in main"
+
+mi_gdb_test "thread" \
+	".*Current thread is 1.*" \
+	"info thread 1"
+
+#=========================
+
+mi_gdb_test "-stack-info-depth --thread 3" \
+	"\\^done,depth=.*" \
+	"-stack-info-depth --thread 3"
+
+mi_gdb_test "thread" \
+	".*Current thread is 1.*" \
+	"info thread 2"
+
+#=========================
+
+mi_gdb_test "-thread-select 3" \
+	"\\^done,.*" \
+	"-thread-select 3"
+
+mi_gdb_test "thread" \
+	".*Current thread is 3.*" \
+	"info thread 3"
+
+#=========================
+
+mi_gdb_test "-thread-select --thread 2 1" \
+	"\\^done,.*" \
+	"-thread-select --thread 2 1"
+
+mi_gdb_test "thread" \
+	".*Current thread is 1.*" \
+	"info thread 4"
+
+#=========================
+
+mi_gdb_test "-thread-select --thread 2 2" \
+	"\\^done,.*" \
+	"-thread-select --thread 2 2"
+
+mi_gdb_test "thread" \
+	".*Current thread is 2.*" \
+	"info thread 5"
+
+#=========================
+
+mi_gdb_test "frame" \
+	".*#0  0x.*" \
+	"frame 1"
+
+mi_gdb_test "-stack-info-frame --thread 2 --frame 1" \
+	"\\^done,frame=\{level=\"1\".*" \
+	"-stack-info-frame 1"
+
+mi_gdb_test "thread" \
+	".*Current thread is 2.*" \
+	"info thread 6"
+
+mi_gdb_test "frame" \
+	".*#0  0x.*" \
+	"frame 2"
+
+#=========================
+
+mi_gdb_test "-stack-info-frame --thread 3 --frame 1" \
+	"\\^done,frame=\{level=\"1\".*" \
+	"-stack-info-frame 2"
+
+mi_gdb_test "thread" \
+	".*Current thread is 2.*" \
+	"info thread 7"
+
+mi_gdb_test "frame" \
+	".*#0  0x.*" \
+	"frame 3"
+
+#=========================
+
+mi_gdb_test "-stack-select-frame --thread 2 --frame 0 1" \
+	"\\^done" \
+	"--stack-select-frame 1"
+
+mi_gdb_test "thread" \
+	".*Current thread is 2.*" \
+	"info thread 8"
+
+mi_gdb_test "frame" \
+	".*#1  0x.*" \
+	"frame 4"
+
+#=========================
+
+mi_gdb_test "-stack-select-frame --thread 2 --frame 2 2" \
+	"\\^done" \
+	"--stack-select-frame 2"
+
+mi_gdb_test "thread" \
+	".*Current thread is 2.*" \
+	"info thread 9"
+
+mi_gdb_test "frame" \
+	".*#2  0x.*" \
+	"frame 5"
+
+#=========================
+
+mi_gdb_test "-stack-select-frame --thread 1 --frame 0 0" \
+	"\\^done" \
+	"--stack-select-frame 3"
+
+mi_gdb_test "thread" \
+	".*Current thread is 1.*" \
+	"info thread 10"
+
+mi_gdb_test "frame" \
+	".*#0  main.*" \
+	"frame 6"
-- 
2.30.2