Re: RFC : Handling breakpoints on archs. with imprecise exceptions.

[Daniel Jacobowitz <drow@false.org>]

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