Re: GDB internal error in pc_in_thread_step_range

[Simon Marchi <simon.marchi@polymtl.ca>]

Hi Eli,

Sorry for the wait.  I don't really have an good answer for you, but I thought I'd
reply anyway, maybe this will help generate ideas.

On 2018-11-18 11:37 a.m., Eli Zaretskii wrote:
>> Date: Mon, 20 Aug 2018 11:08:27 -0400
>> From: Simon Marchi <simon.marchi@polymtl.ca>
>> Cc: gdb@sourceware.org
> 
> A reminder: this is about an internal GDB error that happens on MinGW
> whenever I step out of the 'main' function.
> 
>>>   Temporary breakpoint 1, main () at hello.c:8
>>>   8         printf("hello, world!");
>>>   (gdb) n
>>>   hello, world!9    return 0;
>>>   (gdb)
>>>   10      }
>>>   (gdb)
>>>   0x0040126d in __register_frame_info ()
>>>   (gdb)
>>>   Single stepping until exit from function __register_frame_info,
>>>   which has no line number information.
>>>   infrun.c:2728: internal-error: void resume_1(gdb_signal): Assertion
>>> `pc_in_thread_step_range (pc, tp)' failed.
>>>   A problem internal to GDB has been detected,
>>>   further debugging may prove unreliable.
>>>   Quit this debugging session? (y or n)
>>>
>>> Is it a known problem?
>>
>> Not that I know of.
> 
> I finally got to debugging this.  It happens because:
> 
>   2723          gdb_assert (pc_in_thread_step_range (pc, tp));
>   (top-gdb) p tp->control
>   $22 = {step_resume_breakpoint = 0x0, exception_resume_breakpoint = 0x0,
>     single_step_breakpoints = 0x0, step_range_start = 0x0,
>     step_range_end = 0x1, step_start_function = 0x0, may_range_step = 1,
>     step_frame_id = {stack_addr = 0x28ff70, code_addr = 0x0,
>       special_addr = 0x0, stack_status = FID_STACK_VALID, code_addr_p = 1,
>       special_addr_p = 0, artificial_depth = 0}, step_stack_frame_id = {
>       stack_addr = 0x28ff70, code_addr = 0x0, special_addr = 0x0,
>       stack_status = FID_STACK_VALID, code_addr_p = 1, special_addr_p = 0,
>       artificial_depth = 0}, trap_expected = 0, proceed_to_finish = 0,
>     in_infcall = 0, step_over_calls = STEP_OVER_ALL, stop_step = 0,
>     stop_bpstat = 0x0, stepping_command = 1}
> 
> The step_range_start is zero and step_range_end is 1, which of course
> will not match any value of PC.
> 
> What happens here is that step_1 first zeroes out these members, and
> then fills them by calling find_pc_line_pc_range, called from
> prepare_one_step.  But when I step out of the main program into the
> library epilogue code, there's no line information, and
> prepare_one_step calls find_pc_partial_function, which also doesn't
> find any addresses.  So we fill these members with zero and 1:
> 
>   if (address)
>     {
>       if (pc_in_unmapped_range (pc, section))
> 	*address = overlay_unmapped_address (cache_pc_function_low, section);
>       else
> 	*address = cache_pc_function_low;
>     }
> 
>   if (name)
>     *name = cache_pc_function_name;
> 
>   if (endaddr)
>     {
>       if (pc_in_unmapped_range (pc, section))
> 	{
> 	  /* Because the high address is actually beyond the end of
> 	     the function (and therefore possibly beyond the end of
> 	     the overlay), we must actually convert (high - 1) and
> 	     then add one to that.  */
> 
> 	  *endaddr = 1 + overlay_unmapped_address (cache_pc_function_high - 1,
> 						   section);
> 	}
>       else
> 	*endaddr = cache_pc_function_high;
>     }
> 
> The cached values are zero and 1, correspondingly.

Do you mean that cache_pc_function_low is 0 and cache_pc_function_high is 1?
Do these values even make sense?  They are supposed to hold a range of program
addresses, so 0 and 1 seem bogus.  Maybe this is the result of something going
wrong before?  It would be interesting to understand how they end up with these
values.

If find_pc_partial_function is unable to determine a proper symbol and some proper
bounds, it should return 0.  So if it returns 1 but returns some wrong data,
something is fishy.

Simon