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

[Bruno Larsen <blarsen@redhat.com>]

Ping!

Cheers!
Bruno Larsen

On 5/25/22 15:02, Bruno Larsen wrote:
> 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.
> 
> This commit also changes gdb.reverse/step-reverse.exp to contain a
> recursive function and attempt to both, skip it altogether, and to skip
> the second call from inside the first call, as this setup broke a
> previous version of the patch.
> ---
>   gdb/infrun.c                               | 24 +++++++++
>   gdb/testsuite/gdb.reverse/step-reverse.c   | 16 +++++-
>   gdb/testsuite/gdb.reverse/step-reverse.exp | 59 ++++++++++++++++++++--
>   3 files changed, 95 insertions(+), 4 deletions(-)
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 02c98b50c8c..95fb3227aa3 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -6761,6 +6761,30 @@ process_event_stop_test (struct execution_control_state *ecs)
>       case BPSTAT_WHAT_STEP_RESUME:
>         infrun_debug_printf ("BPSTAT_WHAT_STEP_RESUME");
>   
> +      /* 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))
> +	{
> +	  infrun_debug_printf ("We are not done with recursing yet");
> +	  /* 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;
> +	    }
> +	} else
> +	    infrun_debug_printf ("are we not recursing?");
> +
>         delete_step_resume_breakpoint (ecs->event_thread);
>         if (ecs->event_thread->control.proceed_to_finish
>   	  && execution_direction == EXEC_REVERSE)
> diff --git a/gdb/testsuite/gdb.reverse/step-reverse.c b/gdb/testsuite/gdb.reverse/step-reverse.c
> index aea2a98541d..a390ac2580c 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 (int val){
> +    if (val == 0) return 0;
> +    val /= 2;
> +    if (val>1)
> +	val++;
> +    return recursive_callee (val);	/* RECURSIVE CALL */
> +} /* EXIT RECURSIVE FUNCTION */
> +
>   /* A structure which, we hope, will need to be passed using memcpy.  */
>   struct rhomboidal {
>     int rather_large[100];
> @@ -51,6 +62,9 @@ int main () {
>      y = y + 4;
>      z = z + 5;	/* STEP TEST 2 */
>   
> +   /* Test that next goes over recursive calls too */
> +   recursive_callee (32); /* NEXT OVER THIS RECURSION */
> +
>      /* Test that "next" goes over a call */
>      callee();	/* NEXT OVER THIS CALL */
>   
> @@ -60,7 +74,7 @@ int main () {
>      /* Test "stepi" */
>      a[5] = a[3] - a[4]; /* FINISH TEST */
>      callee();	/* STEPI TEST */
> -
> +
>      /* 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..4f56b4785ca 100644
> --- a/gdb/testsuite/gdb.reverse/step-reverse.exp
> +++ b/gdb/testsuite/gdb.reverse/step-reverse.exp
> @@ -47,9 +47,11 @@ gdb_test "step" ".*STEP TEST 1.*" "step test 1"
>   gdb_test "next 2" ".*NEXT TEST 2.*" "next test 2"
>   gdb_test "step 3" ".*STEP TEST 2.*" "step test 2"
>   
> +# next through a recursive function call
> +gdb_test "next 2" "NEXT OVER THIS CALL.*" "next over recursion"
> +
>   # step over call
>   
> -gdb_test "step" ".*NEXT OVER THIS CALL.*" "step up to call"
>   gdb_test "next" ".*STEP INTO THIS CALL.*" "next over call"
>   
>   # step into call
> @@ -118,7 +120,7 @@ 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 $" {
> +    -re -wrap "NEXTI TEST.*" {
>   	pass "$test_message"
>       }
>       -re "ARRIVED IN CALLEE.*$gdb_prompt $" {
> @@ -143,7 +145,6 @@ gdb_test_multiple "stepi" "$test_message" {
>   ###
>   
>   # Set reverse execution direction
> -
>   gdb_test_no_output "set exec-dir reverse" "set reverse execution"
>   
>   # stepi backward thru return and into a function
> @@ -247,6 +248,58 @@ gdb_test_multiple "step" "$test_message" {
>   
>   gdb_test "next" ".*NEXT OVER THIS CALL.*" "reverse next over call"
>   
> +# Dont reverse the execution direction yet, as we will need another
> +# forward step after this test
> +
> +set step_out 0
> +gdb_test_multiple "next" "reverse next over recursion" {
> +    -re -wrap ".*NEXT OVER THIS RECURSION.*" {
> +	pass "reverse next over recursion"
> +    }
> +    -re -wrap ".*RECURSIVE CALL.*" {
> +	fail "reverse next over recursion"
> +	set step_out 1
> +    }
> +}
> +if { "$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 "reverse-next\n"
> +	    exp_continue
> +	}
> +    }
> +}
> +
> +# Step forward over recursion again so we can test stepping over calls
> +# inside the recursion itself.
> +gdb_test_no_output "set exec-dir forward" "forward again to test recursion"
> +gdb_test "next" "NEXT OVER THIS CALL.*" "reverse next over recursion again"
> +gdb_test_no_output "set exec-dir reverse" "reverse again to test recursion"
> +
> +gdb_test "step" ".*EXIT RECURSIVE FUNCTION.*" "enter recursive function"
> +set step_pass 1
> +gdb_test_multiple "next" "step over recursion inside the recursion" {
> +    -re -wrap ".*EXIT RECURSIVE FUNCTION.*" {
> +	set step_pass 0
> +	send_gdb "next\n"
> +	exp_continue
> +    }
> +    -re -wrap ".*NEXT OVER THIS RECURSION.*" {
> +	if {$step_pass} {
> +	    pass "step over recursion inside the recursion"
> +	} else {
> +	    fail "step over recursion inside the recursion"
> +	}
> +    }
> +    -re -wrap ".*" {
> +	send_gdb "next\n"
> +	exp_continue
> +    }
> +}
> +
>   # step/next backward with count
>   
>   gdb_test "step 3" ".*REVERSE STEP TEST 1.*" "reverse step test 1"