RE: [PATCH v3 0/1] gdb: avoid conversion of SIGSEGV to SIGTRAP on user breakpoints

["Gerlicher, Klaus" <klaus.gerlicher@intel.com>]

Hi,

Kindly pinging.

I think I've lost a bit of momentum here since last November but I had implemented the gdbarch approach here.

Thanks
Klaus


> -----Original Message-----
> From: Klaus Gerlicher <klaus.gerlicher@intel.com>
> Sent: Wednesday, November 27, 2024 12:02 PM
> To: gdb-patches@sourceware.org; aburgess@redhat.com
> Subject: [PATCH v3 0/1] gdb: avoid conversion of SIGSEGV to SIGTRAP on user
> breakpoints
> 
> Hi Andrew,
> 
> thanks for the feedback.
> 
> You replied:
> 
> > But, I wonder if there's a different approach that could be used?
> >
> > I assume that your out of tree architecture with these imprecise page
> > faults has a new gdbarch to represent it.
> >
> > You are limiting the SIGSEGV -> SIGTRAP conversion because, I assume,
> > you've hit cases where a SIGSEGV occurs and then your target has run on
> > and reported the stop at the address of a user breakpoint.  But all
> > you're really doing is reducing the scope for errors.  It could be the
> > case that the SIGSEGV is reported at the site of an internal breakpoint,
> > and then you'll still have issues.
> >
> > So what if, instead, you added a new gdbarch method, something like:
> >
> >   bool gdbarch_has_imprecise_page_faults (struct gdbarch *gdbarch);
> >
> > The default for this, and for all currently in-tree targets, would be to
> > return true.  For your target this will return false.
> >
> > Then in this code we would do:
> >
> >   if (ecs->ws.kind () == TARGET_WAITKIND_STOPPED
> >       && (ecs->ws.sig () == GDB_SIGNAL_ILL
> > 	  || (ecs->ws.sig () == GDB_SIGNAL_SEGV
> >               !gdbarch_has_imprecise_page_faults (gdbarch))
> > 	  || ecs->ws.sig () == GDB_SIGNAL_EMT))
> >
> > How does this approach sound?
> 
> I think for now this would be a viable solution and I implemented it in the V3
> patch.
> 
> However, we had a little discussion internally and we were wondering if this
> now
> feels more like a workaround in a workaround.
> 
> It seems to me that the conversion of any of these signals should really be
> only done for a specific target.  Even though the SIG_ILL and SIG_EMT
> conversions  obviously have no side effects for most targets, I would think
> these should be avoided.
> 
> Do you think there's a way to limit these more specifically or are we unsure
> which targets actually need these? Maybe some of the users are already
> obsolete?
> 
> I would assume it would be difficult to limit to a specific target when we used
> the remote target since we would then have to update GDB server to also
> support
> this.
> 
> I'm of course fine if we fix it with the architecture method but maybe others
> would disagree?
> 
> Thanks
> Klaus
> 
> Gerlicher, Klaus (1):
>   gdb: avoid conversion of SIGSEGV to SIGTRAP on user breakpoints
> 
>  gdb/gdbarch-gen.c         | 22 ++++++++++++++++++++++
>  gdb/gdbarch-gen.h         |  7 +++++++
>  gdb/gdbarch_components.py | 12 ++++++++++++
>  gdb/infrun.c              |  4 +++-
>  4 files changed, 44 insertions(+), 1 deletion(-)
> 
> --
> 2.34.1
> 
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> Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
> Tel: +49 89 99 8853-0, www.intel.de
> Managing Directors: Sean Fennelly, Jeffrey Schneiderman, Tiffany Doon Silva
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> Commercial Register: Amtsgericht Muenchen HRB 186928
> 

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Sean Fennelly, Jeffrey Schneiderman, Tiffany Doon Silva
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928