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

Kevin Buettner
2004-01-19T17:35:14Z

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. */