range stepping: gdbserver (x86 GNU/Linux)

range stepping: gdbserver (x86 GNU/Linux)

This patch adds support for range stepping to GDBserver, teaching it
about vCont;r.

It'd be easy to enable this for all hardware single-step targets
without needing the linux_target_ops hook, however, at least PPC needs
special care, due to the fact that PPC atomic sequences can't be
hardware single-stepped through, a thing which GDBserver doesn't know
about.  So this leaves the support limited to x86/x86_64.

gdb/
2013-05-23  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention GDBserver range stepping support.

gdb/gdbserver/
2013-05-23  Yao Qi  <yao@codesourcery.com>
	    Pedro Alves  <palves@redhat.com>

	* linux-low.c (lwp_in_step_range): New function.
	(linux_wait_1): If the thread was range stepping and stopped
	outside the stepping range, report the stop to GDB.  Otherwise,
	continue stepping.  Add range stepping debug output.
	(linux_set_resume_request): Copy the step range from the resume
	request to the lwp.
	(linux_supports_range_stepping): New.
	(linux_target_ops) <supports_range_stepping>: Set to
	linux_supports_range_stepping.
	* linux-low.h (struct linux_target_ops)
	<supports_range_stepping>: New field.
	(struct lwp_info) <step_range_start, step_range_end>: New fields.
	* linux-x86-low.c (x86_supports_range_stepping): New.
	(the_low_target) <supports_range_stepping>: Set to
	x86_supports_range_stepping.
	* server.c (handle_v_cont): Handle 'r' action.
	(handle_v_requests): Append ";r" if the target supports range
	stepping.
	* target.h (struct thread_resume) <step_range_start,
	step_range_end>: New fields.
	(struct target_ops) <supports_range_stepping>:
	New field.
	(target_supports_range_stepping): New macro.