Read capability tags from memory

Read capability tags from memory

This patch enables capability reads from memory, including the tag bit.

It enables both native GDB and gdbserver to do so.

gdb/ChangeLog:

2021-01-15  Luis Machado  <luis.machado@arm.com>

	* aarch64-linux-nat.c (aarch64_linux_nat_target)
	<read_capability>: New function override.
	(aarch64_linux_nat_target::read_capability): New function.
	(maint_print_cap_from_addr_cmd): New function.
	(add_show_debug_regs_command): Register new maintenance command.
	* aarch64-linux-tdep.c: Include target.h.
	(aarch64_linux_get_cap_tag_from_address): New function.
	(aarch64_linux_init_abi): Register hook for
	gdbarch_get_cap_tag_from_address
	* arch-utils.c (default_get_cap_tag_from_address): New function.
	* arch-utils.h (default_get_cap_tag_from_address): New prototype.
	* configure.nat: Add nat/aarch64-cap-linux.o to the list of object
	files for AArch64-Linux.
	* gdbarch.c: Regenerate.
	* gdbarch.h: Regenerate.
	* gdbarch.sh (get_cap_tag_from_address): New gdbarch hook.
	* nat/aarch64-cap-linux.c: New file.
	* nat/aarch64-cap-linux.h (aarch64_linux_read_capability): New
	prototype.
	* remote.c (remote_target) <read_capability>: New function override.
	(PACKET_qXfer_capability): New enum.
	(remote_target::xfer_partial): Handle TARGET_OBJECT_CAPABILITY.
	(remote_target::read_capability): New member function.
	(_initialize_remote): Add new packet configuration.
	* target-delegates.c: Regenerate.
	* target.c (target_read_capability): New function.
	* target.h (target_object) <TARGET_OBJECT_CAPABILITY>: New enum field.
	(struct target_ops) <read_capability>: New virtual member function.
	(target_read_capability): New prototype.
	* valprint.c (generic_value_print_capability): Handle tags from
	capabilities stored in memory.
	* value.c (value_fetch_lazy_memory): Fetch tag if reading a capability.

gdbserver/ChangeLog

2021-01-15  Luis Machado  <luis.machado@arm.com>

	* configure.srv: Add nat/aarch64-cap-linux.o to the list of object
	files for AArch64-Linux
	* linux-aarch64-low.cc (aarch64_target) <supports_qxfer_capability>
	<qxfer_capability>: New member function overrides.
	(aarch64_target::supports_qxfer_capability): New function.
	(aarch64_target::qxfer_capability): New function.
	* server.cc (handle_qxfer_capability): New function.
	(qxfer_packets): Add "capa" packet.
	* target.cc (process_stratum_target::supports_qxfer_capability)
	(process_stratum_target::qxfer_capability): New functions.
	* target.h (process_stratum_target) <supports_qxfer_capability>
	<qxfer_capability>: New virtual member functions.