[PATCH 1/2] [GDBServer][AArch64] Use the same break instruction as GDB

[Pierre Langlois <pierre dot langlois at arm dot com>]

GDB uses a "brk #0" instruction to perform a software breakpoint while
GDBServer uses an illegal instruction.  Both instructions should match.

When enabling support for the 'Z0' packet, we let GDBServer insert the
breakpoint instruction instead of GDB.  And in case of permanent
breakpoints for example, GDB will check if a breakpoint is inserted in the
inferior with `program_breakpoint_here_p (gdbarch, address)', and
compare the instruction read from the inferior with the breakpoint
instruction.

On AArch64, instructions are always little endian so we need to
represent it as an array of bytes, as done in aarch64-tdep.c.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low.c: Remove comment about endianness.
	(aarch64_breakpoint): Change type to gdb_byte[].  Set to "brk #0".
	(aarch64_breakpoint_at): Change type of insn to gdb_byte[].  Use
	memcmp.
---
 gdb/gdbserver/ChangeLog           |  7 +++++++
 gdb/gdbserver/linux-aarch64-low.c | 14 ++++++++------
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 2528f0f..dde7e9e 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,10 @@
+2015-06-26  Pierre Langlois  <pierre.langlois@arm.com>
+
+	* linux-aarch64-low.c: Remove comment about endianness.
+	(aarch64_breakpoint): Change type to gdb_byte[].  Set to "brk #0".
+	(aarch64_breakpoint_at): Change type of insn to gdb_byte[].  Use
+	memcmp.
+
 2015-06-24  Gary Benson  <gbenson@redhat.com>
 
 	* linux-i386-ipa.c (stdint.h): Do not include.
diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index 043458d..b0a2775 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -295,19 +295,21 @@ aarch64_set_pc (struct regcache *regcache, CORE_ADDR pc)
   supply_register_by_name (regcache, "pc", &newpc);
 }
 
-/* Correct in either endianness.  */
-
 #define aarch64_breakpoint_len 4
 
-static const unsigned long aarch64_breakpoint = 0x00800011;
+/* AArch64 BRK software debug mode instruction.
+   This instruction needs to match gdb/aarch64-tdep.c
+   (aarch64_default_breakpoint).  */
+static const gdb_byte aarch64_breakpoint[] = {0x00, 0x00, 0x20, 0xd4};
 
 static int
 aarch64_breakpoint_at (CORE_ADDR where)
 {
-  unsigned long insn;
+  gdb_byte insn[aarch64_breakpoint_len];
 
-  (*the_target->read_memory) (where, (unsigned char *) &insn, 4);
-  if (insn == aarch64_breakpoint)
+  (*the_target->read_memory) (where, (unsigned char *) &insn,
+			      aarch64_breakpoint_len);
+  if (memcmp (insn, aarch64_breakpoint, aarch64_breakpoint_len) == 0)
     return 1;
 
   return 0;
-- 
2.1.0