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

[Yao Qi <qiyaoltc at gmail dot com>]

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:

2015-10-13  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.
	* nat/aarch64-linux-hw-point.c (aarch64_point_is_aligned):
	Set alignment to 2 for breakpoint.
	(aarch64_handle_breakpoint): Update comments.

gdb/gdbserver:

2015-10-13  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.
---
 gdb/aarch64-linux-nat.c           |  8 ++++++--
 gdb/gdbserver/linux-aarch64-low.c | 18 ++++++++++++------
 gdb/nat/aarch64-linux-hw-point.c  | 15 ++++++++++++---
 3 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
index c9f439f..4d3d55a 100644
--- a/gdb/aarch64-linux-nat.c
+++ b/gdb/aarch64-linux-nat.c
@@ -608,11 +608,13 @@ aarch64_linux_insert_hw_breakpoint (struct target_ops *self,
 {
   int ret;
   CORE_ADDR addr = bp_tgt->placed_address = bp_tgt->reqstd_address;
-  const int len = 4;
+  int len;
   const enum target_hw_bp_type type = hw_execute;
   struct aarch64_debug_reg_state *state
     = aarch64_get_debug_reg_state (ptid_get_pid (inferior_ptid));
 
+  gdbarch_breakpoint_from_pc (gdbarch, &addr, &len);
+
   if (show_debug_regs)
     fprintf_unfiltered
       (gdb_stdlog,
@@ -640,11 +642,13 @@ aarch64_linux_remove_hw_breakpoint (struct target_ops *self,
 {
   int ret;
   CORE_ADDR addr = bp_tgt->placed_address;
-  const int len = 4;
+  int len = 4;
   const enum target_hw_bp_type type = hw_execute;
   struct aarch64_debug_reg_state *state
     = aarch64_get_debug_reg_state (ptid_get_pid (inferior_ptid));
 
+  gdbarch_breakpoint_from_pc (gdbarch, &addr, &len);
+
   if (show_debug_regs)
     fprintf_unfiltered
       (gdb_stdlog, "remove_hw_breakpoint on entry (addr=0x%08lx, len=%d))\n",
diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index 9cefdda..f1ea5a4 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -315,9 +315,12 @@ aarch64_insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
 	ret = -1;
     }
   else
-    ret =
-      aarch64_handle_breakpoint (targ_type, addr, len, 1 /* is_insert */,
-				 state);
+    {
+      if (len == 3)
+	len = 2;
+      ret = aarch64_handle_breakpoint (targ_type, addr, len,
+				       1 /* is_insert */, state);
+    }
 
   if (show_debug_regs)
     aarch64_show_debug_reg_state (state, "insert_point", addr, len,
@@ -353,9 +356,12 @@ aarch64_remove_point (enum raw_bkpt_type type, CORE_ADDR addr,
       aarch64_handle_watchpoint (targ_type, addr, len, 0 /* is_insert */,
 				 state);
   else
-    ret =
-      aarch64_handle_breakpoint (targ_type, addr, len, 0 /* is_insert */,
-				 state);
+    {
+      if (len == 3)
+	len = 2;
+      ret = aarch64_handle_breakpoint (targ_type, addr, len,
+				       0 /* is_insert */,  state);
+    }
 
   if (show_debug_regs)
     aarch64_show_debug_reg_state (state, "remove_point", addr, len,
diff --git a/gdb/nat/aarch64-linux-hw-point.c b/gdb/nat/aarch64-linux-hw-point.c
index bca6ec1..d15e518 100644
--- a/gdb/nat/aarch64-linux-hw-point.c
+++ b/gdb/nat/aarch64-linux-hw-point.c
@@ -112,8 +112,17 @@ aarch64_point_encode_ctrl_reg (enum target_hw_bp_type type, int len)
 static int
 aarch64_point_is_aligned (int is_watchpoint, CORE_ADDR addr, int len)
 {
-  unsigned int alignment = is_watchpoint ? AARCH64_HWP_ALIGNMENT
-    : AARCH64_HBP_ALIGNMENT;
+  unsigned int alignment = 0;
+
+  if (is_watchpoint)
+    alignment = AARCH64_HWP_ALIGNMENT;
+  else
+    {
+      /* Set alignment to 2 only if the current process is 32-bit,
+	 since thumb instruction can be 2-byte aligned.  Otherwise, set
+	 alignment to AARCH64_HBP_ALIGNMENT.  */
+      alignment = 2;
+    }
 
   if (addr & (alignment - 1))
     return 0;
@@ -445,7 +454,7 @@ aarch64_handle_breakpoint (enum target_hw_bp_type type, CORE_ADDR addr,
 			   struct aarch64_debug_reg_state *state)
 {
   /* The hardware breakpoint on AArch64 should always be 4-byte
-     aligned.  */
+     aligned, but on AArch32, it can be 2-byte aligned.  */
   if (!aarch64_point_is_aligned (0 /* is_watchpoint */ , addr, len))
     return -1;
 
-- 
1.9.1