[PATCHv3] aarch64: detect atomic sequences like other ll/sc architectures

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index bba10d8..e0cab6d 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -2509,6 +2509,83 @@  value_of_aarch64_user_reg (struct frame_info *frame, const void *baton)
 }
 
 
+/* Implement the "software_single_step" gdbarch method, needed to
+   single step through atomic sequences on AArch64.  */
+
+static int
+aarch64_software_single_step (struct frame_info *frame)
+{
+  struct gdbarch *gdbarch = get_frame_arch (frame);
+  struct address_space *aspace = get_frame_address_space (frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  const int insn_size = 4;
+  const int atomic_sequence_length = 16; /* Instruction sequence length.  */
+  CORE_ADDR pc = get_frame_pc (frame);
+  CORE_ADDR breaks[2] = { -1, -1 };
+  CORE_ADDR loc = pc;
+  CORE_ADDR closing_insn = 0;
+  uint32_t insn = read_memory_unsigned_integer (loc, insn_size, byte_order);
+  int index;
+  int insn_count;
+  int bc_insn_count = 0; /* Conditional branch instruction count.  */
+  int last_breakpoint = 0; /* Defaults to 0 (no breakpoints placed).  */
+
+  /* Look for a Load Exclusive instruction which begins the sequence.  */
+  if (!decode_masked_match (insn, 0x3fc00000, 0x08400000))
+    return 0;
+
+  for (insn_count = 0; insn_count < atomic_sequence_length; ++insn_count)
+    {
+      int32_t offset;
+      unsigned cond;
+
+      loc += insn_size;
+      insn = read_memory_unsigned_integer (loc, insn_size, byte_order);
+
+      /* Check if the instruction is a conditional branch.  */
+      if (decode_bcond (loc, insn, &cond, &offset))
+	{
+
+	  if (bc_insn_count >= 1)
+	    return 0;
+
+	  /* It is, so we'll try to set a breakpoint at the destination.  */
+	  breaks[1] = loc + offset;
+
+	  bc_insn_count++;
+	  last_breakpoint++;
+	}
+
+      /* Look for the Store Exclusive which closes the atomic sequence.  */
+      if (decode_masked_match (insn, 0x3fc00000, 0x08000000))
+	{
+          closing_insn = loc;
+	  break;
+	}
+    }
+
+  /* We didn't find a closing Store Exclusive instruction, fall back.  */
+  if (!closing_insn)
+    return 0;
+
+  /* Insert breakpoint after the end of the atomic sequence.  */
+  breaks[0] = loc + insn_size;
+
+  /* Check for duplicated breakpoints, and also check that the second
+     breakpoint is not within the atomic sequence.  */
+  if (last_breakpoint
+      && (breaks[1] == breaks[0]
+	  || (breaks[1] >= pc && breaks[1] <= closing_insn)))
+    last_breakpoint = 0;
+
+  /* Insert the breakpoint at the end of the sequence, and one at the
+     destination of the conditional branch, if it exists.  */
+  for (index = 0; index <= last_breakpoint; index++)
+    insert_single_step_breakpoint (gdbarch, aspace, breaks[index]);
+
+  return 1;
+}
+
 /* Initialize the current architecture based on INFO.  If possible,
    re-use an architecture from ARCHES, which is a list of
    architectures already created during this debugging session.
@@ -2624,6 +2701,7 @@  aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_breakpoint_from_pc (gdbarch, aarch64_breakpoint_from_pc);
   set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
   set_gdbarch_have_nonsteppable_watchpoint (gdbarch, 1);
+  set_gdbarch_software_single_step (gdbarch, aarch64_software_single_step);
 
   /* Information about registers, etc.  */
   set_gdbarch_sp_regnum (gdbarch, AARCH64_SP_REGNUM);
diff --git a/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c
new file mode 100644
index 0000000..9a73c7a
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c
@@ -0,0 +1,48 @@ 
+/* This file is part of GDB, the GNU debugger.
+
+   Copyright 2008-2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int main(void)
+{
+  unsigned long tmp, cond;
+  unsigned long dword = 0;
+
+  /* Test that we can step over ldxr/stxr. This sequence should step from
+     ldxr to the following __asm __volatile.  */
+  __asm __volatile ("1:     ldxr    %0,%2\n"                             \
+                    "       cmp     %0,#1\n"                             \
+                    "       b.eq    out\n"                               \
+                    "       add     %0,%0,1\n"                           \
+                    "       stxr    %w1,%0,%2\n"                         \
+                    "       cbnz    %w1,1b"                              \
+                    : "=&r" (tmp), "=&r" (cond), "+Q" (dword)            \
+                    : : "memory");
+
+  /* This sequence should take the conditional branch and step from ldxr
+     to the return dword line.  */
+  __asm __volatile ("1:     ldxr    %0,%2\n"                             \
+                    "       cmp     %0,#1\n"                             \
+                    "       b.eq    out\n"                               \
+                    "       add     %0,%0,1\n"                           \
+                    "       stxr    %w1,%0,%2\n"                         \
+                    "       cbnz    %w1,1b\n"                            \
+                    : "=&r" (tmp), "=&r" (cond), "+Q" (dword)            \
+                    : : "memory");
+
+  dword = -1;
+__asm __volatile ("out:\n");
+  return dword;
+}
diff --git a/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp
new file mode 100644
index 0000000..377aebc
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp
@@ -0,0 +1,48 @@ 
+# Copyright 2008-2014 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+#
+# This file is part of the gdb testsuite.
+
+# Test single stepping through atomic sequences beginning with
+# a ldxr instruction and ending with a stxr instruction.
+
+if {![istarget "aarch64*"]} {
+    verbose "Skipping ${gdb_test_file_name}."
+    return
+}
+
+standard_testfile
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return -1
+}
+
+if ![runto_main] {
+    untested "could not run to main"
+    return -1
+}
+
+gdb_breakpoint "[gdb_get_line_number "ldxr"]" \
+  "Breakpoint $decimal at $hex" \
+  "Set the breakpoint at the start of the sequence"
+
+gdb_test "continue" "Continuing.*Breakpoint $decimal.*" \
+  "Continue until breakpoint"
+
+gdb_test "next" ".*__asm __volatile.*" \
+  "Step through the ldxr/stxr sequence"
+
+gdb_test "next" ".*return dword.*" \
+  "Stepped through sequence through conditional branch"