X86: reverse-finish fix

PR record/29927  - reverse-finish requires two reverse next instructions to
reach previous source line

Currently on X86, when executing the finish command in reverse, gdb does a
single step from the first instruction in the callee to get back to the
caller.  GDB stops on the last instruction in the source code line where
the call was made.  When stopped at the last instruction of the source code
line, a reverse next or step command will stop at the first instruction
of the same source code line thus requiring two step/next commands to
reach the previous source code line.  It should only require one step/next
command to reach the previous source code line.

By contrast, a reverse next or step command from the first line in a
function stops at the first instruction in the source code line where the
call was made.

This patch fixes the reverse finish command so it will stop at the first
instruction of the source line where the function call was made.  The
behavior on X86 for the reverse-finish command now matches doing a
reverse-next from the beginning of the function.

The proceed_to_finish flag in struct thread_control_state is no longer
used.  This patch removes the declaration, initialization and setting of
the flag.

This patch requires a number of regression tests to be updated.  Test
gdb.mi/mi-reverse.exp no longer needs to execute two steps to get to the
previous line.  The gdb output for tests gdb.reverse/until-precsave.exp
and gdb.reverse/until-reverse.exp changed slightly.  The expected result in
tests gdb.reverse/amd64-failcall-reverse.exp and
gdb.reverse/singlejmp-reverse.exp are updated to the correct expected
result.

This patch adds a new test gdb.reverse/finish-reverse-next.exp to test the
reverse-finish command when returning from the entry point and from the
body of the function.

The step_until proceedure in test gdb.reverse/step-indirect-call-thunk.exp
was moved to lib/gdb.exp and renamed cmd_until.

The patch has been tested on X86 and PowerPC to verify no additional
regression failures occured.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29927

gdb/gdbthread.h

@@ -150,10 +150,6 @@ struct thread_control_state
      the finished single step.  */
   int trap_expected = 0;
 
-  /* Nonzero if the thread is being proceeded for a "finish" command
-     or a similar situation when return value should be printed.  */
-  int proceed_to_finish = 0;
-
   /* Nonzero if the thread is being proceeded for an inferior function
      call.  */
   int in_infcall = 0;

gdb/infcall.c

@@ -625,9 +625,6 @@ run_inferior_call (std::unique_ptr<call_thread_fsm> sm,
 
   disable_watchpoints_before_interactive_call_start ();
 
-  /* We want to print return value, please...  */
-  call_thread->control.proceed_to_finish = 1;
-
   try
     {
       /* Infcalls run synchronously, in the foreground.  */

gdb/infcmd.c

@@ -1719,19 +1719,10 @@ finish_backward (struct finish_command_fsm *sm)
 
   sal = find_pc_line (func_addr, 0);
 
-  tp->control.proceed_to_finish = 1;
-  /* Special case: if we're sitting at the function entry point,
-     then all we need to do is take a reverse singlestep.  We
-     don't need to set a breakpoint, and indeed it would do us
-     no good to do so.
-
-     Note that this can only happen at frame #0, since there's
-     no way that a function up the stack can have a return address
-     that's equal to its entry point.  */
+  frame_info_ptr frame = get_selected_frame (nullptr);
 
   if (sal.pc != pc)
     {
-      frame_info_ptr frame = get_selected_frame (nullptr);
       struct gdbarch *gdbarch = get_frame_arch (frame);
 
       /* Set a step-resume at the function's entry point.  Once that's
@@ -1741,16 +1732,22 @@ finish_backward (struct finish_command_fsm *sm)
       sr_sal.pspace = get_frame_program_space (frame);
       insert_step_resume_breakpoint_at_sal (gdbarch,
 					    sr_sal, null_frame_id);
-
-      proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
     }
   else
     {
-      /* We're almost there -- we just need to back up by one more
-	 single-step.  */
-      tp->control.step_range_start = tp->control.step_range_end = 1;
-      proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
+      /* We are exactly at the function entry point.  Note that this
+	 can only happen at frame #0.
+
+	 When setting a step range, need to call set_step_info
+	 to setup the current_line/symtab fields as well.  */
+      set_step_info (tp, frame, find_pc_line (pc, 0));
+
+      /* Return using a step range so we will keep stepping back
+	 to the first instruction in the source code line.  */
+      tp->control.step_range_start = sal.pc;
+      tp->control.step_range_end = sal.pc;
     }
+  proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
 }
 
 /* finish_forward -- helper function for finish_command.  FRAME is the
@@ -1776,9 +1773,6 @@ finish_forward (struct finish_command_fsm *sm, frame_info_ptr frame)
 
   set_longjmp_breakpoint (tp, frame_id);
 
-  /* We want to print return value, please...  */
-  tp->control.proceed_to_finish = 1;
-
   proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
 }
 

gdb/infrun.c

@@ -2748,8 +2748,6 @@ clear_proceed_status_thread (struct thread_info *tp)
 
   tp->control.stop_step = 0;
 
-  tp->control.proceed_to_finish = 0;
-
   tp->control.stepping_command = 0;
 
   /* Discard any remaining commands or status from previous stop.  */
@@ -6737,31 +6735,27 @@ process_event_stop_test (struct execution_control_state *ecs)
 
     case BPSTAT_WHAT_STEP_RESUME:
       infrun_debug_printf ("BPSTAT_WHAT_STEP_RESUME");
-
       delete_step_resume_breakpoint (ecs->event_thread);
-      if (ecs->event_thread->control.proceed_to_finish
-	  && execution_direction == EXEC_REVERSE)
+      fill_in_stop_func (gdbarch, ecs);
+
+      if (execution_direction == EXEC_REVERSE)
 	{
 	  struct thread_info *tp = ecs->event_thread;
+	  /* We are finishing a function in reverse or stepping over a function
+	     call in reverse, and just hit the step-resume breakpoint at the
+	     start address of the function, and we're almost there -- just need
+	     to back up to the function call.  */
 
-	  /* We are finishing a function in reverse, and just hit the
-	     step-resume breakpoint at the start address of the
-	     function, and we're almost there -- just need to back up
-	     by one more single-step, which should take us back to the
-	     function call.  */
-	  tp->control.step_range_start = tp->control.step_range_end = 1;
-	  keep_going (ecs);
-	  return;
-	}
-      fill_in_stop_func (gdbarch, ecs);
-      if (ecs->event_thread->stop_pc () == ecs->stop_func_start
-	  && execution_direction == EXEC_REVERSE)
-	{
-	  /* We are stepping over a function call in reverse, and just
-	     hit the step-resume breakpoint at the start address of
-	     the function.  Go back to single-stepping, which should
-	     take us back to the function call.  */
-	  ecs->event_thread->stepping_over_breakpoint = 1;
+	  stop_pc_sal = find_pc_line (ecs->event_thread->stop_pc (), 0);
+
+	  /* When setting a step range, need to call set_step_info
+	     to setup the current_line/symtab fields as well.  */
+	  set_step_info (tp, frame, stop_pc_sal);
+
+	  /* Return using a step range so we will keep stepping back to the
+	     first instruction in the source code line.  */
+	  tp->control.step_range_start = ecs->stop_func_start;
+	  tp->control.step_range_end = ecs->stop_func_start;
 	  keep_going (ecs);
 	  return;
 	}

gdb/testsuite/gdb.mi/mi-reverse.exp

@@ -95,15 +95,10 @@ proc test_controlled_execution_reverse {} {
 	"basics.c" $line_main_callme_1 "" \
 	"reverse finish from callme"
 
-    # Test exec-reverse-next
-    #   It takes two steps to get back to the previous line,
-    #   as the first step moves us to the start of the current line,
-    #   and the one after that moves back to the previous line.
-
-    mi_execute_to "exec-next --reverse 2" \
+    mi_execute_to "exec-next --reverse" \
  	"end-stepping-range" "main" "" \
  	"basics.c" $line_main_hello "" \
- 	"reverse next to get over the call to do_nothing"
+	"reverse next to get over the call to do_nothing"
 
     # Test exec-reverse-step
 

gdb/testsuite/gdb.reverse/amd64-tailcall-reverse.exp

@@ -42,6 +42,5 @@ if [supports_process_record] {
 gdb_test "next" {f \(\);} "next to f"
 gdb_test "next" {v = 3;} "next to v = 3"
 
-# FAIL was:
-# 29        g ();
-gdb_test "reverse-next" {f \(\);}
+# Reverse step back into f ().  Puts us at call to g () in function f ().
+gdb_test "reverse-next" {g \(\);}

gdb/testsuite/gdb.reverse/finish-reverse-next.c

@@ -0,0 +1,48 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2012-2023 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/>.  */
+
+/* The reverse finish command should return from a function and stop on
+   the first instruction of the source line where the function call is made.
+   Specifically, the behavior should match doing a reverse next from the
+   first instruction in the function.  GDB should only require one reverse
+   step or next statement to reach the previous source code line.
+
+   This test verifies the fix for gdb bugzilla:
+
+   https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+*/
+
+int
+function1 (int a, int b)   // FUNCTION1
+{
+  int ret = 0;
+
+  ret = a + b;
+  return ret;
+}
+
+int
+main(int argc, char* argv[])
+{
+  int a, b;
+
+  a = 1;
+  b = 5;
+
+  function1 (a, b);   // CALL FUNCTION
+  return 0;
+}

gdb/testsuite/gdb.reverse/finish-reverse-next.exp

@@ -0,0 +1,104 @@
+# Copyright 2008-2023 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/>.  */
+
+# This file is part of the GDB testsuite.  It tests reverse stepping.
+# Lots of code borrowed from "step-test.exp".
+
+# The reverse finish command should return from a function and stop on
+# the first instruction of the source line where the function call is made.
+# Specifically, the behavior should match doing a reverse next from the
+# first instruction in the function.  GDB should only take one reverse step
+# or next statement to reach the previous source code line.
+
+# This testcase verifies the reverse-finish command stops at the first
+# instruction in the source code line where the function was called.  There
+# are two scenarios that must be checked:
+#   1) gdb is at the entry point instruction for the function
+#   2) gdb is in the body of the function.
+
+# This test verifies the fix for gdb bugzilla:
+#   https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+
+if ![supports_reverse] {
+    return
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
+    return -1
+}
+
+runto_main
+set target_remote [gdb_is_target_remote]
+
+if [supports_process_record] {
+    # Activate process record/replay.
+    gdb_test_no_output "record" "turn on process record for test1"
+}
+
+
+### TEST 1: reverse finish from the entry point instruction in
+### function1.
+
+# Set breakpoint at call to function1 in main.
+set bp_FUNCTION [gdb_get_line_number "CALL FUNCTION" $srcfile]
+gdb_breakpoint $srcfile:$bp_FUNCTION temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+    "stopped at function1 entry point instruction to stepi into function" \
+    ".*$srcfile:$bp_FUNCTION\r\n.*"
+
+# stepi until we see "{" indicating we entered function1
+repeat_cmd_until "stepi" "CALL FUNCTION" "{" "stepi into function1 call"
+
+gdb_test "reverse-finish" ".*function1 \\(a, b\\);   // CALL FUNCTION.*" \
+    "reverse-finish function1 "
+
+# Check to make sure we stopped at the first instruction in the source code
+# line.  It should only take one reverse next command to get to the previous
+# source line.   If GDB stops at the last instruction in the source code line
+# it will take two reverse next instructions to get to the previous source
+# line.
+gdb_test "reverse-next" ".*b = 5;.*" "reverse next at b = 5, call from function"
+
+# Clear the recorded log.
+gdb_test "record stop"  "Process record is stopped.*" \
+    "turn off process record for test1"
+gdb_test_no_output "record" "turn on process record for test2"
+
+
+### TEST 2: reverse finish from the body of function1.
+
+# Set breakpoint at call to function1 in main.
+gdb_breakpoint $srcfile:$bp_FUNCTION temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+    "at function1 entry point instruction to step to body of function" \
+    ".*$srcfile:$bp_FUNCTION\r\n.*"
+
+# do a step instruction to get to the body of the function
+gdb_test "step" ".*int ret = 0;.*" "step test 1"
+
+gdb_test "reverse-finish" ".*function1 \\(a, b\\);   // CALL FUNCTION.*" \
+    "reverse-finish function1 call from function body"
+
+# Check to make sure we stopped at the first instruction in the source code
+# line.  It should only take one reverse next command to get to the previous
+# source line.
+gdb_test "reverse-next" ".*b = 5;.*" \
+    "reverse next at b = 5, from function body"

gdb/testsuite/gdb.reverse/singlejmp-reverse.exp

@@ -54,7 +54,4 @@ gdb_test "next" {v = 3;} "next to v = 3"
 # {
 gdb_test "reverse-step" {nodebug \(\);}
 
-# FAIL was:
-# No more reverse-execution history.
-# {
-gdb_test "reverse-next" {f \(\);}
+gdb_test "reverse-next" {g \(\);}

gdb/testsuite/gdb.reverse/step-indirect-call-thunk.exp

@@ -36,39 +36,6 @@ if { ![runto_main] } {
     return -1
 }
 
-# Do repeated stepping COMMANDs in order to reach TARGET from CURRENT
-#
-#  COMMAND is a stepping command
-#  CURRENT is a string matching the current location
-#  TARGET  is a string matching the target location
-#  TEST    is the test name
-#
-# The function issues repeated COMMANDs as long as the location matches
-# CURRENT up to a maximum of 100 steps.
-#
-# TEST passes if the resulting location matches TARGET and fails
-# otherwise.
-#
-proc step_until { command current target test } {
-    global gdb_prompt
-
-    set count 0
-    gdb_test_multiple "$command" "$test" {
-        -re "$current.*$gdb_prompt $" {
-            incr count
-            if { $count < 100 } {
-                send_gdb "$command\n"
-                exp_continue
-            } else {
-                fail "$test"
-            }
-        }
-        -re "$target.*$gdb_prompt $" {
-            pass "$test"
-        }
-    }
-}
-
 gdb_test_no_output "record"
 gdb_test "next" ".*" "record trace"
 
@@ -88,20 +55,20 @@ gdb_test "reverse-next" "apply\.2.*" \
     "reverse-step through thunks and over inc"
 
 # We can use instruction stepping to step into thunks.
-step_until "stepi" "apply\.2" "indirect_thunk" "stepi into call thunk"
-step_until "stepi" "indirect_thunk" "inc" \
+repeat_cmd_until "stepi" "apply\.2" "indirect_thunk" "stepi into call thunk"
+repeat_cmd_until "stepi" "indirect_thunk" "inc" \
     "stepi out of call thunk into inc"
 set alphanum_re "\[a-zA-Z0-9\]"
 set pic_thunk_re  "__$alphanum_re*\\.get_pc_thunk\\.$alphanum_re* \\(\\)"
-step_until "stepi" "(inc|$pic_thunk_re)" "return_thunk" "stepi into return thunk"
-step_until "stepi" "return_thunk" "apply" \
+repeat_cmd_until "stepi" "(inc|$pic_thunk_re)" "return_thunk" "stepi into return thunk"
+repeat_cmd_until "stepi" "return_thunk" "apply" \
     "stepi out of return thunk back into apply"
 
-step_until "reverse-stepi" "apply" "return_thunk" \
+repeat_cmd_until "reverse-stepi" "apply" "return_thunk" \
     "reverse-stepi into return thunk"
-step_until "reverse-stepi" "return_thunk" "inc" \
+repeat_cmd_until "reverse-stepi" "return_thunk" "inc" \
     "reverse-stepi out of return thunk into inc"
-step_until "reverse-stepi" "(inc|$pic_thunk_re)" "indirect_thunk" \
+repeat_cmd_until "reverse-stepi" "(inc|$pic_thunk_re)" "indirect_thunk" \
     "reverse-stepi into call thunk"
-step_until "reverse-stepi" "indirect_thunk" "apply" \
+repeat_cmd_until "reverse-stepi" "indirect_thunk" "apply" \
     "reverse-stepi out of call thunk into apply"

gdb/testsuite/gdb.reverse/until-precsave.exp

@@ -138,7 +138,7 @@ gdb_test "advance marker2" \
 # Finish out to main scope (backward)
 
 gdb_test "finish" \
-    " in main .*$srcfile:$bp_location20.*" \
+    "main .*$srcfile:$bp_location20.*" \
     "reverse-finish from marker2"
 
 # Advance backward to last line of factorial (outer invocation)

gdb/testsuite/gdb.reverse/until-reverse.exp

@@ -111,7 +111,7 @@ gdb_test "advance marker2" \
 # Finish out to main scope (backward)
 
 gdb_test "finish" \
-    " in main .*$srcfile:$bp_location20.*" \
+    "main .*$srcfile:$bp_location20.*" \
     "reverse-finish from marker2"
 
 # Advance backward to last line of factorial (outer invocation)

gdb/testsuite/lib/gdb.exp

@@ -9261,6 +9261,39 @@ proc gdb_step_until { regexp {test_name ""} {max_steps 10} } {
     }
 }
 
+# Do repeated stepping COMMANDs in order to reach TARGET from CURRENT
+#
+#  COMMAND is a stepping command
+#  CURRENT is a string matching the current location
+#  TARGET  is a string matching the target location
+#  TEST    is the test name
+#
+# The function issues repeated COMMANDs as long as the location matches
+# CURRENT up to a maximum of 100 steps.
+#
+# TEST passes if the resulting location matches TARGET and fails
+# otherwise.
+
+proc repeat_cmd_until { command current target test } {
+    global gdb_prompt
+
+    set count 0
+    gdb_test_multiple "$command" "$test" {
+	-re "$current.*$gdb_prompt $" {
+	    incr count
+	    if { $count < 100 } {
+		send_gdb "$command\n"
+		exp_continue
+	    } else {
+		fail "$test"
+	    }
+	}
+	-re "$target.*$gdb_prompt $" {
+	    pass "$test"
+	}
+    }
+}
+
 # Check if the compiler emits epilogue information associated
 # with the closing brace or with the last statement line.
 #