Re: [PATCH] arm software watchpoint: return to epilogue

[Pedro Alves <palves@redhat.com>]

On 08/06/2014 04:18 AM, Yao Qi wrote:

> It doesn't work in this case, because program returns from func's
> epilogue back to jumper's epilogue [2], GDB thinks the program is
> still within the epilogue, but in fact it goes to a different one.
> When PC points at [2], the sp-restore instruction is to be
> executed, so the stack frame isn't destroyed yet and we can still
> use the frame mechanism reliably.


> What this patch does is to restrict the epilogue matching that let
> GDB think the first SP restore instruction isn't part of the epilogue,
> and fall back to use frame mechanism.  

This gdbarch hook's name is a bit misleading -- your comment above kind
of makes it sound like the patch is doing some kind of target specific
hack, while this is exactly how the gdbarch hook is specified:

# A target might have problems with watchpoints as soon as the stack
# frame of the current function has been destroyed.  This mostly happens
# as the first action in a funtion's epilogue.  in_function_epilogue_p()
# is defined to return a non-zero value if either the given addr is one
                                                                 ^^^^^^
# instruction after the stack destroying instruction up to the trailing
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# return instruction or if we can figure out that the stack frame has
# already been invalidated regardless of the value of addr.  Targets
# which don't suffer from that problem could just let this functionality
# untouched.
m:int:in_function_epilogue_p:CORE_ADDR addr:addr:0:generic_in_function_epilogue_p::0

> The patch is tested in arm-none-eabi and arm-none-linux-gnueabi with
> various multilibs.  OK to apply?

This is OK with Will's comment addressed.

Thanks,
Pedro Alves