[RFC] Possible bug with i386 watchpoints on several targets.

[Pierre Muller <muller at cerbere dot u-strasbg dot fr>]

At 16:45 30/11/2001 , Eli Zaretskii a écrit:
> > Date: Fri, 30 Nov 2001 16:17:27 +0100
> > From: Pierre Muller <muller@cerbere.u-strasbg.fr>
> > 
> >     What do we do about this?
> > I proposed to add a call to i386_cleanup_dregs
> > for all targets using the standard 
> > i386 hardware watchpoints, but 
> > Eli seems still not convinced by my reports....
>
>You don't need to convince me (the port I'm responsible for _does_
>use i386_cleanup_dregs, after all ;-).  You need to convince Mark
>Kettenis.  I'm sure that if you post a test program and a full recipe
>to reproduce the problem, and then show the patch which makes the
>problem go away, Mark will happily accept it.

   The way to check if the bug exist is easy:

   take gdb (5.1 or current snapshot)
compiled with debug info and 
run
   ./gdb ./gdb
on the newly generated executable.
(preferabily in the compilation dir,
which will ensure that you get (top-gdb) prompt
for the debugger and (gdb) for the debuggee).

use the following command
(top-gdb) watch gdb_stdout
(top-gdb) r
Here you should get a stop due to the setting of gdb_stdout value.
(top-gdb) cont
you should now reach the debuggee command prompt,
simply quit.
(gdb) quit
and rerun the same executable without any watchpoint modification.
(top-gdb) run
if the bug that I found on both win32 (without i386_cleanup_deregs call)
and on current (a few days old) CVS for linux.
You won't get any stop on the second run.

The fix is not that obvious, because I am still a bit unclear
about wher it should be put:
   the i386_cleanup_dregs should be called (in my opinion)
both when a program is killed and when a program
terminates normally.

   But linux does seem to use generic_mourn_inferior,
so for this target it would probably require that we 
change this into a target specific function.

PS: Eli, did you check the go32v2 target if you kill the program after
the watchpoint is reached, sorry, I still can't get GDB to compile for djgpp
on my win2000.


Pierre Muller
Institut Charles Sadron
6,rue Boussingault
F 67083 STRASBOURG CEDEX (France)
mailto:muller@ics.u-strasbg.fr
Phone : (33)-3-88-41-40-07  Fax : (33)-3-88-41-40-99