[RFC] infrun.c: Fix infinite loop caused by breakpoint adjustment

[RFC] infrun.c: Fix infinite loop caused by breakpoint adjustment

[Kevin Buettner]

Any comments on the patch below?

It fixes an infinite loop caused by attempting to run to a location
to which it's architecturally impossible to set a breakpoint at.  (It's
quite easy to reproduce this problem on FR-V.  Just step into some
library code which has been compiled with optimization.)

Since it touches infrun.c, and since a lot of developers are on
holiday at this time of year, I'll wait until January 15 to commit it.
Hopefully, that'll give everyone who'd like to comment on this patch
a chance to look at it.

Kevin

	* infrun.c (step_into_function): Account for possible breakpoint
	adjustment when computing ``stop_func_start''.

Index: infrun.c
===================================================================
RCS file: /cvs/src/src/gdb/infrun.c,v
retrieving revision 1.122
diff -u -p -r1.122 infrun.c
--- infrun.c	25 Nov 2003 16:01:36 -0000	1.122
+++ infrun.c	18 Dec 2003 19:34:53 -0000
@@ -2762,6 +2762,18 @@ step_into_function (struct execution_con
       && ecs->sal.end < ecs->stop_func_end)
     ecs->stop_func_start = ecs->sal.end;
 
+  /* Architectures which require breakpoint adjustment might not be able
+     to place a breakpoint at the computed address.  If so, the test
+     ``ecs->stop_func_start == stop_pc'' will never succeed.  Adjust
+     ecs->stop_func_start to an address at which a breakpoint may be
+     legitimately placed.  */
+  if (gdbarch_adjust_breakpoint_address_p (current_gdbarch))
+    {
+      ecs->stop_func_start
+	= gdbarch_adjust_breakpoint_address (current_gdbarch,
+	                                     ecs->stop_func_start);
+    }
+
   if (ecs->stop_func_start == stop_pc)
     {
       /* We are already there: stop now.  */

Re: [RFC] infrun.c: Fix infinite loop caused by breakpoint adjustment

[Andrew Cagney]

> Any comments on the patch below?

Can this paragraph (or something like it) should be included in the code 
change?  That way the reader will better understand exactly what goes 
wrong and for which architecture.

> It fixes an infinite loop caused by attempting to run to a location
> to which it's architecturally impossible to set a breakpoint at.  (It's
> quite easy to reproduce this problem on FR-V.  Just step into some
> library code which has been compiled with optimization.)

enjoy,
Andrew

> Since it touches infrun.c, and since a lot of developers are on
> holiday at this time of year, I'll wait until January 15 to commit it.
> Hopefully, that'll give everyone who'd like to comment on this patch
> a chance to look at it.
> 
> Kevin
> 
> 	* infrun.c (step_into_function): Account for possible breakpoint
> 	adjustment when computing ``stop_func_start''.
> 
> Index: infrun.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/infrun.c,v
> retrieving revision 1.122
> diff -u -p -r1.122 infrun.c
> --- infrun.c	25 Nov 2003 16:01:36 -0000	1.122
> +++ infrun.c	18 Dec 2003 19:34:53 -0000
> @@ -2762,6 +2762,18 @@ step_into_function (struct execution_con
>        && ecs->sal.end < ecs->stop_func_end)
>      ecs->stop_func_start = ecs->sal.end;
>  
> +  /* Architectures which require breakpoint adjustment might not be able
> +     to place a breakpoint at the computed address.  If so, the test
> +     ``ecs->stop_func_start == stop_pc'' will never succeed.  Adjust
> +     ecs->stop_func_start to an address at which a breakpoint may be
> +     legitimately placed.  */
> +  if (gdbarch_adjust_breakpoint_address_p (current_gdbarch))
> +    {
> +      ecs->stop_func_start
> +	= gdbarch_adjust_breakpoint_address (current_gdbarch,
> +	                                     ecs->stop_func_start);
> +    }
> +
>    if (ecs->stop_func_start == stop_pc)
>      {
>        /* We are already there: stop now.  */
> 
> 

Re: [RFC] infrun.c: Fix infinite loop caused by breakpoint adjustment

[Kevin Buettner]

On Sun, 11 Jan 2004 16:03:32 -0500
Andrew Cagney <cagney@gnu.org> wrote:

> > Any comments on the patch below?
> 
> Can this paragraph (or something like it) should be included in the code 
> change?  That way the reader will better understand exactly what goes 
> wrong and for which architecture.
> 
> > It fixes an infinite loop caused by attempting to run to a location
> > to which it's architecturally impossible to set a breakpoint at.  (It's
> > quite easy to reproduce this problem on FR-V.  Just step into some
> > library code which has been compiled with optimization.)

Okay, here's what I committed:

	* infrun.c (step_into_function): Account for possible breakpoint
	adjustment when computing ``stop_func_start''.

Index: infrun.c
===================================================================
RCS file: /cvs/src/src/gdb/infrun.c,v
retrieving revision 1.129
diff -u -p -r1.129 infrun.c
--- infrun.c	19 Jan 2004 01:20:11 -0000	1.129
+++ infrun.c	19 Jan 2004 17:25:48 -0000
@@ -2757,6 +2757,29 @@ step_into_function (struct execution_con
       && ecs->sal.end < ecs->stop_func_end)
     ecs->stop_func_start = ecs->sal.end;
 
+  /* Architectures which require breakpoint adjustment might not be able
+     to place a breakpoint at the computed address.  If so, the test
+     ``ecs->stop_func_start == stop_pc'' will never succeed.  Adjust
+     ecs->stop_func_start to an address at which a breakpoint may be
+     legitimately placed.
+     
+     Note:  kevinb/2004-01-19:  On FR-V, if this adjustment is not
+     made, GDB will enter an infinite loop when stepping through
+     optimized code consisting of VLIW instructions which contain
+     subinstructions corresponding to different source lines.  On
+     FR-V, it's not permitted to place a breakpoint on any but the
+     first subinstruction of a VLIW instruction.  When a breakpoint is
+     set, GDB will adjust the breakpoint address to the beginning of
+     the VLIW instruction.  Thus, we need to make the corresponding
+     adjustment here when computing the stop address.  */
+     
+  if (gdbarch_adjust_breakpoint_address_p (current_gdbarch))
+    {
+      ecs->stop_func_start
+	= gdbarch_adjust_breakpoint_address (current_gdbarch,
+	                                     ecs->stop_func_start);
+    }
+
   if (ecs->stop_func_start == stop_pc)
     {
       /* We are already there: stop now.  */