[patch/rfc] Rewrite decr-pc logic, eliminate step_sp

[Andrew Cagney]

+  if (currently_stepping (ecs))
+    {
+      if (SOFTWARE_SINGLE_STEP_P ())
+    {
+      if (singlestep_breakpoints_inserted_p
+          && prev_pc == breakpoint_pc)
+        /* If we're software-single-stepping, assume we hit one of
+           the inserted software breakpoints.  */
+        write_pc_pid (breakpoint_pc, ecs->ptid);
+    }


I'm pretty sure that won't work.  prev_pc is where we were stopped
before we decided to single step.  breakpoint_pc is where, if we have
hit a breakpoint, the breakpoint would be.  They won't be equal;
breakpoint_pc will be the following instruction, or the target of a
branch if *prev_pc was a taken branch.  The old code assumes we hit a
breakpoint if we stopped with SIGTRAP with singlestep_breakpoints_inserted_p
- any reason not to keep that behavior?


It's plain wrong.  I'm pretty sure that, when doing the thread-hop, singlestep_breakpoints_inserted_p holds, but current_stepping() doesn't.

I think Alpha OSF/1 and Alpha NetBSD are the only current
software-single-step and decr-pc targets, which makes this case a
little hard to test - at least OSF/1 had dreadful test results already,
I'm not sure about NetBSD.  Might want to verify that it isn't
catastrophic, at least.
The rest of it looks right to me, though I had to stare at it for
the last twenty minutes or so.


I gave up staring at the old code, it made no sense.

Attached is a revision.
I've checked this in.  In addition to PPC (h/w single step) and i386 
(decr pc after break) I gave it a sniff test on alpha GNU/Linux (hacked 
to use s/w single step).

Andrew

2004-05-09  Andrew Cagney  <cagney@redhat.com>

	* infrun.c (adjust_pc_after_break): Rewrite decr logic,
	eliminate reference to step_sp.
	(struct execution_control_state, init_execution_control_state)
	(handle_inferior_event, keep_going): Delete update_step_sp and
	step_sp.
	* infcmd.c (step_sp): Note that variable is unused.