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Re: RFC: Centralize DECR_PC_AFTER_BREAK handling from infrun

On Sun, Jan 18, 2004 at 10:19:10AM -0500, Daniel Jacobowitz wrote:
> > > +  /* If we've hit a breakpoint, we'll be stopped with SIGTRAP.  */
> > > +  if (ecs->ws.kind != TARGET_WAITKIND_STOPPED)
> > > +    return;
> > > +
> > > +  if (ecs->ws.value.sig != TARGET_SIGNAL_TRAP)
> > > +    return;
> > 
> > The original code didn't check these conditions, right?  So why add
> > them here?  (Also, the comment doesn't seem to describe the two
> > tests, only the second one.)
> The comment does describe both tests; if != TARGET_WAITKIND_STOPPED,
> then we aren't stopped by a signal.  The other waitkinds correspond to
> things like exiting and catchpoints, and with the exception of some
> complications in the FORKED/EXECD cases, stop_signal will not get set
> to SIGTRAP.  Also, the original code did check these conditions, though
> somewhat indirectly:
>   if (stop_signal == TARGET_SIGNAL_TRAP)
>     {
>       /* Check if a regular breakpoint has been hit before checking
>          for a potential single step breakpoint. Otherwise, GDB will
>          not see this breakpoint hit when stepping onto breakpoints.  */
> Oh, hum, that's for the first set (thread hit thread-specific BP for a
> different thread).  The second thread does this:
>   if (stop_signal == TARGET_SIGNAL_TRAP
>       || (breakpoints_inserted &&
>           (stop_signal == TARGET_SIGNAL_ILL
>            || stop_signal == TARGET_SIGNAL_EMT))
>       || stop_soon == STOP_QUIETLY
>       || stop_soon == STOP_QUIETLY_NO_SIGSTOP)
> The stop_soon's aren't relevant here, since they're handled before
> DECR_PC_AFTER_BREAK, but the ILL/EMT are relevant.  They should be
> added to adjust_pc_after_break - thanks!

Actually, I'm not sure they should.  The question is, on an operating
system such that hitting a breakpoint causes SIGILL, should
DECR_PC_AFTER_BREAK be applied?  I don't have a machine such that
breakpoints cause SIGILL, but I tested  x86 and alpha (both
DECR_PC_AFTER_BREAK targets).  On x86 a SIGILL leaves the PC pointing
at the beginning of the illegal instruction, and on Alpha a SIGILL
leaves the PC pointing to the second instruction after the illegal one.
In neither case does that match the behavior of DECR_PC_AFTER_BREAK. 

So this will become a comment also.

Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

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