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Re: RFC : Handling breakpoints on archs. with imprecise exceptions.
- From: Daniel Jacobowitz <drow at false dot org>
- To: Ramana Radhakrishnan <ramana dot radhakrishnan at codito dot com>
- Cc: gdb at sources dot redhat dot com, amit bhor <amit dot bhor at codito dot com>
- Date: Thu, 24 Mar 2005 15:38:14 -0500
- Subject: Re: RFC : Handling breakpoints on archs. with imprecise exceptions.
- References: <42431904.7010708@codito.com>
On Fri, Mar 25, 2005 at 01:16:12AM +0530, Ramana Radhakrishnan wrote:
> Hi,
>
> While looking at a GDB port to a processor that has
> imprecise exceptions/ interrupts i.e. the equivalent of a
> software breakpoint would require 4 instructions to stop.
> With my research I was unable to find any GDB port that
> needed to handle such a case.
>
> The mechanism that is in mind is the following for setting
> breakpoints.
It sounds plausible, although messy. Does a single-instruction
branch always give you enough range to reach a breakpoint table?
I suspect you could handle this by wrapping gdbarch_read_pc, so that
a "breakpoint" at a particular "pc" would appear to stop there rather
than in the table. Be sure to restore the correct pc at that point.
That and breakpoint_from_pc may be all the hooks you need. And maybe
hooks in target_insert_breakpoint/target_remove_breakpoint to reference
count.
> a. Define gdbarch_adjust_breakpoint_address in the backend
> to store the mapping in the backend for the PC at which
> breakpoint has been set to the actual value for the PC where
> the breakpoint would be reported to have been hit.
>
> b. Define deprecated_target_wait_hook in the backend to
> restore the actual value of the PC for GDB to continue with
> its work.However as this is a deprecated hook I would not
> like to use this in a new port.
>
> c. Add a new notify_backend_breakpoint_deleted_hook since
> the backend needs notification for the breakpoint being
> deleted and hence free an entry in the breakpoint table.
You should be hooking insert/remove breakpoint, not add/delete user
breakpoint.
Does gdbarch_read_pc do everything you need for the wait_hook? You can
update the PC from there if necessary.
--
Daniel Jacobowitz
CodeSourcery, LLC