[PATCH] gdb/reverse: Fix stepping over recursive functions

[Bruno Larsen]

Currently, when using GDB to do reverse debugging, if we try to use the
command "reverse next" to skip a recursive function, instead of skipping
all of the recursive calls and stopping in the previous line, we stop at
the second to last recursive call, and need to manually step backwards
until we leave the first call.  This is well documented in PR gdb/16678.

This bug happens because when GDB notices that a reverse step has
entered into a function, GDB will add a step_resume_breakpoint at the
start of the function, then single step out of the prologue once that
breakpoint is hit.  Recursion poses a problem because that breakpoint will
be hit many times before GDB should actually stop the inferior.  To fix
this issue, when the step_resume_breakpoint is hit (and GDB is executing
backwards), we analyze if the caller of the frame is the original frame
where we started the "reverse next", and if it is, GDB will stop the
inferior, otherwise GDB will just ignore the breakpoint.
---
 gdb/infrun.c                               | 22 ++++++++++++++++++
 gdb/testsuite/gdb.reverse/step-reverse.c   | 13 +++++++++++
 gdb/testsuite/gdb.reverse/step-reverse.exp | 26 +++++++++++++++++++++-
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 02c98b50c8c..ee42f7dfa34 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -6233,6 +6233,28 @@ handle_signal_stop (struct execution_control_state *ecs)
 	  infrun_debug_printf ("[%s] hit its single-step breakpoint",
 			       ecs->ptid.to_string ().c_str ());
 	}
+
+      /* If we are executing backwards, we are doing a "next" and the
+	 current frame is not the same as where we started, the
+	 step_resume_breakpoint we have just hit has been added to the start
+	 of a function so we can skip the whle function.  However, if we are
+	 skipping a recursive call, we only want to act as if we hit the
+	 breakpoint only when the caller of the current frame is the original
+	 frame we were single stepping from.  */
+      if (execution_direction == EXEC_REVERSE
+	  && ecs->event_thread->control.step_over_calls == STEP_OVER_ALL
+	  && !frame_id_eq (get_stack_frame_id (get_current_frame ()),
+			   ecs->event_thread->control.step_stack_frame_id))
+	{
+	  /* If the caller's ID is not the same as the starting frame, we
+	     can ignore this breakpoint.  */
+	  if (!frame_id_eq (frame_unwind_caller_id (get_current_frame ()),
+			    ecs->event_thread->control.step_stack_frame_id))
+	    {
+	      keep_going (ecs);
+	      return;
+	    }
+	}
     }
   delete_just_stopped_threads_single_step_breakpoints ();
 
diff --git a/gdb/testsuite/gdb.reverse/step-reverse.c b/gdb/testsuite/gdb.reverse/step-reverse.c
index aea2a98541d..958d4b297b0 100644
--- a/gdb/testsuite/gdb.reverse/step-reverse.c
+++ b/gdb/testsuite/gdb.reverse/step-reverse.c
@@ -26,6 +26,17 @@ int callee() {		/* ENTER CALLEE */
   return myglob++;	/* ARRIVED IN CALLEE */
 }			/* RETURN FROM CALLEE */
 
+/* We need to make this function take more than a single instruction
+   to run, otherwise it could hide PR gdb/16678, as reverse execution can
+   step over a single-instruction function.  */
+int recursive_callee (){
+    if (myglob == 0) return 0;
+    myglob /= 2;
+    if (myglob>1)
+	myglob++;
+    return recursive_callee ();	/* REVERSE NEXT FAIL */
+}
+
 /* A structure which, we hope, will need to be passed using memcpy.  */
 struct rhomboidal {
   int rather_large[100];
@@ -61,6 +72,8 @@ int main () {
    a[5] = a[3] - a[4]; /* FINISH TEST */
    callee();	/* STEPI TEST */
    
+   recursive_callee (); /* NEXT OVER THIS RECURSION */
+
    /* Test "nexti" */
    callee();	/* NEXTI TEST */
 
diff --git a/gdb/testsuite/gdb.reverse/step-reverse.exp b/gdb/testsuite/gdb.reverse/step-reverse.exp
index 997b62604d5..4238675431e 100644
--- a/gdb/testsuite/gdb.reverse/step-reverse.exp
+++ b/gdb/testsuite/gdb.reverse/step-reverse.exp
@@ -118,7 +118,7 @@ gdb_test_multiple "stepi" "$test_message" {
 
 set test_message "stepi back from function call"
 gdb_test_multiple "stepi" "$test_message" {
-    -re "NEXTI TEST.*$gdb_prompt $" {
+    -re -wrap "NEXT OVER THIS RECURSION.*" {
 	pass "$test_message"
     }
     -re "ARRIVED IN CALLEE.*$gdb_prompt $" {
@@ -138,6 +138,9 @@ gdb_test_multiple "stepi" "$test_message" {
     }
 }
 
+# next through a recursive function call
+gdb_test "next" "NEXTI TEST.*" "next over recursion"
+
 ###
 ###
 ###
@@ -145,6 +148,27 @@ gdb_test_multiple "stepi" "$test_message" {
 # Set reverse execution direction
 
 gdb_test_no_output "set exec-dir reverse" "set reverse execution"
+set step_out 0
+gdb_test_multiple "next" "reverse next over recursion" {
+    -re -wrap ".*NEXT OVER THIS RECURSION.*" {
+	pass "reverse next over recursion"
+    }
+    -re -wrap ".*REVERSE NEXT FAIL.*" {
+	fail "reverse next over recursion"
+	set step_out 1
+    }
+}
+if { "$step_out" == 1 } {
+    gdb_test_multiple "next" "stepping out of recursion" {
+	-re -wrap "NEXT OVER THIS RECURSION.*" {
+	    set step_out 0
+	}
+	-re -wrap ".*" {
+	    send_gdb "next\n"
+	    exp_continue
+	}
+    }
+}
 
 # stepi backward thru return and into a function
 
-- 
2.31.1