aarch64 multi-arch part 6: HW breakpoint on unaligned address

aarch64 multi-arch part 6: HW breakpoint on unaligned address

Nowadays, both aarch64 GDB and linux kernel assumes that address for
setting breakpoint should be 4-byte aligned.  However that is not true
after we support multi-arch, because thumb instruction can be at 2-byte
aligned address.  Patch http://lists.infradead.org/pipermail/linux-arm-kernel/2015-October/375141.html
to linux kernel is to teach kernel to handle 2-byte aligned address for
HW breakpoint, while this patch is to teach aarch64 GDB handle 2-byte
aligned address.

First of all, we call gdbarch_breakpoint_from_pc to get the instruction
length rather than using hard-coded 4.  Secondly, in GDBserver, we set
length back to 2 if it is 3, because GDB encode 3 in it to indicate it
is a 32-bit thumb breakpoint.  Then we relax the address alignment
check from 4-byte aligned to 2-byte aligned.

This patch enables some tests (such as gdb.base/break-idempotent.exp,
gdb.base/cond-eval-mode.exp, gdb.base/watchpoint-reuse-slot.exp,) and
fixes many fails (such as gdb.base/hbreak2.exp) when the program is
compiled in thumb mode on aarch64.

Regression tested on aarch64-linux, both native and gdbserver.  This
is the last patch of multi-arch work.

gdb:

2015-10-15  Yao Qi  <yao.qi@linaro.org>

	* aarch64-linux-nat.c (aarch64_linux_insert_hw_breakpoint):
	Call gdbarch_breakpoint_from_pc to instruction length.
	(aarch64_linux_remove_hw_breakpoint): Likewise.
	* common/common-regcache.h (regcache_register_size): Declare.
	* nat/aarch64-linux-hw-point.c: Include "common-regcache.h".
	(aarch64_point_is_aligned): Set alignment to 2 for breakpoint if
	the process is 32bit, otherwise set alignment to 4.
	(aarch64_handle_breakpoint): Update comments.
	* regcache.c (regcache_register_size): New function.

gdb/gdbserver:

2015-10-15  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c (aarch64_insert_point): Set len to 2
	if it is 3.
	(aarch64_remove_point): Likewise.
	* regcache.c (regcache_register_size): New function.