Re: [hatari-devel] Debugger 'n' command

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 04/11/2016 01:01 AM, Nicolas Pomarède wrote:
> Le 10/04/2016 23:40, Eero Tamminen a écrit :
>
> > The reason why it's not currently supported, is that branching
> > can also be forwards.  Then "n" command breakpoint for the next
> > instruction might never terminate, which IMHO is worse than
> > lacking support for skipping loops.
> >
> > Does somebody feel adding support for determining when instruction
> > at PC is a branch going backwards?  :-)
>
> For bne/beq it would be more complicated, but in the case of dbcc it
> will mostly be backward ; dbcc uses 2 words, 1 with the opcode, 1 with
> the displacement ; if the the 2nd word is <0, then it will go backward
> and a breakpoint after the dbcc will work.
>
> format for DBcc is : 0101 cccc 1100 1rrr  . so if ( opcode & 0x50A8 ) ==
> 0x50a8, then you have a DBcc and you can check the next word.

Does the attached patch work OK?


	- Eero

diff -r 9ffbbc92221e src/debug/debugcpu.c
--- a/src/debug/debugcpu.c	Mon Apr 11 01:52:50 2016 +0300
+++ b/src/debug/debugcpu.c	Mon Apr 11 01:53:52 2016 +0300
@@ -537,15 +537,25 @@
 		Uint32 optype, nextpc;
 
 		optype = DebugCpu_OpcodeType();
-		/* can this instruction be stepped normally? */
-		if (optype != CALL_SUBROUTINE && optype != CALL_EXCEPTION)
+		/* should this instruction be stepped normally, or is it
+		 * - subroutine call
+		 * - exception
+		 * - loop branch backwards
+		 */
+		if (optype == CALL_SUBROUTINE ||
+		    optype == CALL_EXCEPTION ||
+		    (optype == CALL_BRANCH &&
+		     (STMemory_ReadWord(M68000_GetPC()) & 0xf0f8) == 0x50c8 &&
+		     (Sint16)STMemory_ReadWord(M68000_GetPC()+SIZE_WORD) < 0))
+		{
+			nextpc = Disasm_GetNextPC(M68000_GetPC());
+			sprintf(command, "pc=$%x :once :quiet\n", nextpc);
+		}
+		else
 		{
 			nCpuSteps = 1;
 			return DEBUGGER_END;
 		}
-
-		nextpc = Disasm_GetNextPC(M68000_GetPC());
-		sprintf(command, "pc=$%x :once :quiet\n", nextpc);
 	}
 	/* use breakpoint, not steps */
 	if (BreakCond_Command(command, false))