[PINGv3] [PATCH] gdb/reverse: Fix stepping over recursive functions

[Bruno Larsen <blarsen@redhat.com>]

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"