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Re: [rfc] Strip Thumb bit from PC returned by arm_get_longjmp_target
- From: "Ulrich Weigand" <uweigand at de dot ibm dot com>
- To: matthew dot gretton-dann at arm dot com (Matthew Gretton-Dann)
- Cc: gdb-patches at sourceware dot org
- Date: Fri, 20 Aug 2010 14:00:10 +0200 (CEST)
- Subject: Re: [rfc] Strip Thumb bit from PC returned by arm_get_longjmp_target
Matthew Gretton-Dann wrote:
> On Thu, 2010-08-19 at 10:49 +0200, Ulrich Weigand wrote:
> > Actually, it turns out this new patch doesn't work. It leads to:
> >
> > Breakpoint 4 at 0x84ec: file ../../../gdb-head/gdb/testsuite/gdb.threads/threxit-hop-specific.c, line 47.^M
> > (gdb) next^M
> > ^M
> > Program received signal SIGTRAP, Trace/breakpoint trap.^M
> >
> > This happens because GDB now no longer recognizes the PC address
> > when the breakpoint trap arrives. The PC is compared against
> > the breakpoint location's loc->address value -- which now has the
> > Thumb bit set, but the PC doesn't.
> >
> > Note that while the Thumb bit gets removes in arm_breakpoint_from_pc,
> > this affects only loc->placed_address, not loc->address.
> >
> > This seems to indicate that in fact, breakpoint addresses must
> > *not* have the Thumb bit set ...
> >
> > Do you have a case where this works for you?
>
> I don't have a case. I think this means that the original patch is the
> correct one for the moment - but I'm not a maintainer so this isn't an
> approval.
OK, thanks for your feedback. I'm happy to wait for Richard's approval ...
> Also, looking at the code in arm_adjust_breakpoint_address I think there
> are other cases that may cause the failure you are seeing above (for
> instance when using Thumb-2 in the absence of mapping symbols and
> setting the breakpoint on 0x8001).
I'm now wondering whether it can in fact ever happen that an address with
the Thumb bit set can come into arm_adjust_breakpoint_address; it seems
that (except for the longjmp target case) no such values are ever exposed.
Am I missing a possible path here?
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com