[PINGv5] [PATCH] gdb/reverse: Fix stepping over recursive functions

[Bruno Larsen <blarsen@redhat.com>]

ping!

Cheers!
Bruno Larsen

On 6/29/22 15:46, Bruno Larsen wrote:
> ping!
> 
> Cheers!
> Bruno Larsen
> 
> On 6/22/22 15:49, Bruno Larsen wrote:
>> ping!
>>
>> Cheers!
>> Bruno Larsen
>>
>> On 6/15/22 16:21, Bruno Larsen wrote:
>>> ping!
>>>
>>> Cheers!
>>> Bruno Larsen
>>>
>>> On 6/8/22 08:17, Bruno Larsen wrote:
>>>> 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"