[PATCH v3 03/10] Refactor queries for hardware and software single stepping support in GDBServer.

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

Before this patch there was only one call: can_hardware_single_step. Its
implementation was a check on breakpoint_reinsert_addr if NULL it assumed
that the target could hardware single step.

This patch prepares for the case where this is not true anymore.

In order to improve software single stepping in GDBServer the
breakpoint_reinsert_addr operation of targets that had a very simple
software implementation used only for stepping over thread creation events
will be removed.

This will create a case where a target does not support hardware single
step and has the operation breakpoint_reinsert_addr set to NULL, thus
can_hardware_single_step needs to be implemented another way.

A new target operation supports_hardware_single_step is introduced and is
to return true if the target does support such a feature, support for the
feature is manually hardcoded.

Note that the hardware single step support was enabled as per the current
behavior, I did not check if tile for example really has ptrace singlestep
support but since the current implementation assumed it had, I kept it
that way.

No regressions on Ubuntu 14.04 on ARMv7 and x86.
With gdbserver-{native,extended} / { -marm -mthumb }

Compilation tested on: aarch64,arm,bfind,crisv32,m32r,ppc,s390,tic6x,tile,
xtensa.
Not tested : sh.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low.c (aarch64_supports_hardware_single_step):
	New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-arm-low.c (arm_supports_hardware_single_step): New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-bfin-low.c (bfin_supports_hardware_single_step): New function.
	(struct linux_target_ops) <bfin_supports_hardware_single_step>:
	Initialize.
	* linux-crisv32-low.c (cris_supports_hardware_single_step):
	New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-low.c (can_hardware_single_step): Use
	supports_hardware_single_step.
	(can_software_single_step): New function.
	(start_step_over): Call can_software_single_step.
	(linux_supports_hardware_single_step): New function.
	(struct target_ops) <supports_software_single_step>: Initialize.
	* linux-low.h (struct linux_target_ops)
	<supports_hardware_single_step>: Initialize.
	* linux-m32r-low.c (m32r_supports_hardware_single_step): New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-ppc-low.c (ppc_supports_hardware_single_step): New function.
	(struct linux_target_ops) <supports_hardware_single_step> Initialize.
	* linux-s390-low.c (s390_supports_hardware_single_step): New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-sh-low.c (sh_supports_hardware_single_step): New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-tic6x-low.c (tic6x_supports_hardware_single_step): New function.
	(struct linux_target_ops) <tic6x_supports_hardware_single_step>:
	Initialize.
	* linux-tile-low.c (tile_supports_hardware_single_step): New function.
	(struct linux_target_ops) <tile_supports_hardware_single_step>:
	Initialize.
	* linux-x86-low.c (x86_supports_hardware_single_step) New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* linux-xtensa-low.c (xtensa_supports_hardware_single_step):
	New function.
	(struct linux_target_ops) <supports_hardware_single_step>: Initialize.
	* target.h (struct target_ops): <supports_software_single_step>:
	New field.
	(target_supports_software_single_step): New macro.
---
 gdb/gdbserver/linux-aarch64-low.c | 10 ++++++++++
 gdb/gdbserver/linux-arm-low.c     | 11 ++++++++++-
 gdb/gdbserver/linux-bfin-low.c    | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/linux-crisv32-low.c | 24 ++++++++++++++++++++++++
 gdb/gdbserver/linux-low.c         | 33 ++++++++++++++++++++++++++++-----
 gdb/gdbserver/linux-low.h         |  3 +++
 gdb/gdbserver/linux-m32r-low.c    | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/linux-ppc-low.c     | 22 ++++++++++++++++++++++
 gdb/gdbserver/linux-s390-low.c    | 22 ++++++++++++++++++++++
 gdb/gdbserver/linux-sh-low.c      | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/linux-tic6x-low.c   | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/linux-tile-low.c    | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/linux-x86-low.c     | 11 +++++++++++
 gdb/gdbserver/linux-xtensa-low.c  | 29 +++++++++++++++++++++++++++++
 gdb/gdbserver/target.h            |  7 +++++++
 15 files changed, 311 insertions(+), 6 deletions(-)

diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index cb78666..17798ff 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -2944,6 +2944,14 @@ aarch64_sw_breakpoint_from_kind (int kind, int *size)
   return aarch64_breakpoint;
 }
 
+/* Support for hardware single step.  */
+
+static int
+aarch64_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 struct linux_target_ops the_low_target =
 {
   aarch64_arch_setup,
@@ -2977,6 +2985,8 @@ struct linux_target_ops the_low_target =
   aarch64_emit_ops,
   aarch64_get_min_fast_tracepoint_insn_len,
   aarch64_supports_range_stepping,
+  NULL, /* breakpoint_kind_from_current_state */
+  aarch64_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
index 6f37f58..0c78888 100644
--- a/gdb/gdbserver/linux-arm-low.c
+++ b/gdb/gdbserver/linux-arm-low.c
@@ -902,6 +902,14 @@ arm_arch_setup (void)
     have_ptrace_getregset = 0;
 }
 
+/* Support for hardware single step.  */
+
+static int
+arm_supports_hardware_single_step (void)
+{
+  return 0;
+}
+
 /* Register sets without using PTRACE_GETREGSET.  */
 
 static struct regset_info arm_regsets[] = {
@@ -1058,7 +1066,8 @@ struct linux_target_ops the_low_target = {
   NULL, /* emit_ops */
   NULL, /* get_min_fast_tracepoint_insn_len */
   NULL, /* supports_range_stepping */
-  arm_breakpoint_kind_from_current_state
+  arm_breakpoint_kind_from_current_state,
+  arm_supports_hardware_single_step
 };
 
 void
diff --git a/gdb/gdbserver/linux-bfin-low.c b/gdb/gdbserver/linux-bfin-low.c
index d3b83fc..912d253 100644
--- a/gdb/gdbserver/linux-bfin-low.c
+++ b/gdb/gdbserver/linux-bfin-low.c
@@ -105,6 +105,14 @@ bfin_arch_setup (void)
   current_process ()->tdesc = tdesc_bfin;
 }
 
+/* Support for hardware single step.  */
+
+static int
+bfin_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct usrregs_info bfin_usrregs_info =
   {
     bfin_num_regs,
@@ -136,6 +144,27 @@ struct linux_target_ops the_low_target = {
   NULL, /* breakpoint_reinsert_addr */
   2,
   bfin_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  bfin_supports_hardware_single_step,
 };
 
 
diff --git a/gdb/gdbserver/linux-crisv32-low.c b/gdb/gdbserver/linux-crisv32-low.c
index 8d9ef04..4f9afa6 100644
--- a/gdb/gdbserver/linux-crisv32-low.c
+++ b/gdb/gdbserver/linux-crisv32-low.c
@@ -388,6 +388,14 @@ cris_arch_setup (void)
   current_process ()->tdesc = tdesc_crisv32;
 }
 
+/* Support for hardware single step.  */
+
+static int
+cris_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct regset_info cris_regsets[] = {
   { PTRACE_GETREGS, PTRACE_SETREGS, 0, cris_num_regs * 4,
     GENERAL_REGS, cris_fill_gregset, cris_store_gregset },
@@ -439,6 +447,22 @@ struct linux_target_ops the_low_target = {
   cris_remove_point,
   cris_stopped_by_watchpoint,
   cris_stopped_data_address,
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  cris_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 63ac8b3..f793a78 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -269,13 +269,24 @@ static void complete_ongoing_step_over (void);
    being stepped.  */
 ptid_t step_over_bkpt;
 
-/* True if the low target can hardware single-step.  Such targets
-   don't need a BREAKPOINT_REINSERT_ADDR callback.  */
+/* True if the low target can hardware single-step.  */
 
 static int
 can_hardware_single_step (void)
 {
-  return (the_low_target.breakpoint_reinsert_addr == NULL);
+  if (the_low_target.supports_hardware_single_step != NULL)
+    return the_low_target.supports_hardware_single_step ();
+  else
+    return 0;
+}
+
+/* True if the low target can software single-step.  Such targets
+   implement the BREAKPOINT_REINSERT_ADDR callback.  */
+
+static int
+can_software_single_step (void)
+{
+  return (the_low_target.breakpoint_reinsert_addr != NULL);
 }
 
 /* True if the low target supports memory breakpoints.  If so, we'll
@@ -4426,12 +4437,17 @@ start_step_over (struct lwp_info *lwp)
     {
       step = 1;
     }
-  else
+  else if (can_software_single_step ())
     {
       CORE_ADDR raddr = (*the_low_target.breakpoint_reinsert_addr) ();
       set_reinsert_breakpoint (raddr);
       step = 0;
     }
+  else
+    {
+      internal_error (__FILE__, __LINE__,
+		      "stepping is not implemented on this target");
+    }
 
   current_thread = saved_thread;
 
@@ -5626,6 +5642,12 @@ linux_supports_hardware_single_step (void)
 }
 
 static int
+linux_supports_software_single_step (void)
+{
+  return can_software_single_step ();
+}
+
+static int
 linux_stopped_by_watchpoint (void)
 {
   struct lwp_info *lwp = get_thread_lwp (current_thread);
@@ -7064,7 +7086,8 @@ static struct target_ops linux_target_ops = {
   linux_mntns_readlink,
   linux_breakpoint_kind_from_pc,
   linux_sw_breakpoint_from_kind,
-  linux_breakpoint_kind_from_current_state
+  linux_breakpoint_kind_from_current_state,
+  linux_supports_software_single_step
 };
 
 static void
diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index fb15136..2e1f32f 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -236,6 +236,9 @@ struct linux_target_ops
 
   /* See target.h.  */
   int (*breakpoint_kind_from_current_state) (CORE_ADDR *pcptr);
+
+  /* See target.h.  */
+  int (*supports_hardware_single_step) (void);
 };
 
 extern struct linux_target_ops the_low_target;
diff --git a/gdb/gdbserver/linux-m32r-low.c b/gdb/gdbserver/linux-m32r-low.c
index bb1002f..c6d79b6 100644
--- a/gdb/gdbserver/linux-m32r-low.c
+++ b/gdb/gdbserver/linux-m32r-low.c
@@ -103,6 +103,14 @@ m32r_arch_setup (void)
   current_process ()->tdesc = tdesc_m32r;
 }
 
+/* Support for hardware single step.  */
+
+static int
+m32r_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct usrregs_info m32r_usrregs_info =
   {
     m32r_num_regs,
@@ -134,6 +142,27 @@ struct linux_target_ops the_low_target = {
   NULL,
   0,
   m32r_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  m32r_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-ppc-low.c b/gdb/gdbserver/linux-ppc-low.c
index 995a725..decee86 100644
--- a/gdb/gdbserver/linux-ppc-low.c
+++ b/gdb/gdbserver/linux-ppc-low.c
@@ -547,6 +547,14 @@ ppc_store_evrregset (struct regcache *regcache, const void *buf)
   supply_register_by_name (regcache, "spefscr", &regset->spefscr);
 }
 
+/* Support for hardware single step.  */
+
+static int
+ppc_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct regset_info ppc_regsets[] = {
   /* List the extra register sets before GENERAL_REGS.  That way we will
      fetch them every time, but still fall back to PTRACE_PEEKUSER for the
@@ -705,6 +713,20 @@ struct linux_target_ops the_low_target = {
   NULL,
   ppc_collect_ptrace_register,
   ppc_supply_ptrace_register,
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  ppc_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-s390-low.c b/gdb/gdbserver/linux-s390-low.c
index efede2d..7127373 100644
--- a/gdb/gdbserver/linux-s390-low.c
+++ b/gdb/gdbserver/linux-s390-low.c
@@ -609,6 +609,14 @@ s390_breakpoint_at (CORE_ADDR pc)
   return memcmp (c, s390_breakpoint, s390_breakpoint_len) == 0;
 }
 
+/* Support for hardware single step.  */
+
+static int
+s390_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct usrregs_info s390_usrregs_info =
   {
     s390_num_regs,
@@ -686,6 +694,20 @@ struct linux_target_ops the_low_target = {
   NULL,
   s390_collect_ptrace_register,
   s390_supply_ptrace_register,
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  s390_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-sh-low.c b/gdb/gdbserver/linux-sh-low.c
index 207e87e..1b3189b 100644
--- a/gdb/gdbserver/linux-sh-low.c
+++ b/gdb/gdbserver/linux-sh-low.c
@@ -100,6 +100,14 @@ sh_breakpoint_at (CORE_ADDR where)
   return 0;
 }
 
+/* Support for hardware single step.  */
+
+static int
+sh_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 /* Provide only a fill function for the general register set.  ps_lgetregs
    will use this for NPTL support.  */
 
@@ -162,6 +170,27 @@ struct linux_target_ops the_low_target = {
   NULL,
   0,
   sh_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  sh_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-tic6x-low.c b/gdb/gdbserver/linux-tic6x-low.c
index cf8b5fb..e4aba15 100644
--- a/gdb/gdbserver/linux-tic6x-low.c
+++ b/gdb/gdbserver/linux-tic6x-low.c
@@ -341,6 +341,14 @@ tic6x_arch_setup (void)
   current_process ()->tdesc = tic6x_read_description ();
 }
 
+/* Support for hardware single step.  */
+
+static int
+tic6x_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static struct regsets_info tic6x_regsets_info =
   {
     tic6x_regsets, /* regsets */
@@ -380,6 +388,27 @@ struct linux_target_ops the_low_target = {
   NULL,
   0,
   tic6x_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  tic6x_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-tile-low.c b/gdb/gdbserver/linux-tile-low.c
index 47ca245..6f16355 100644
--- a/gdb/gdbserver/linux-tile-low.c
+++ b/gdb/gdbserver/linux-tile-low.c
@@ -181,6 +181,14 @@ tile_arch_setup (void)
     current_process ()->tdesc = tdesc_tilegx;
 }
 
+/* Support for hardware single step.  */
+
+static int
+tile_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 
 struct linux_target_ops the_low_target =
 {
@@ -196,6 +204,27 @@ struct linux_target_ops the_low_target =
   NULL,
   0,
   tile_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  tile_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index 89ec4e5..7c63919 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -3258,6 +3258,15 @@ x86_supports_range_stepping (void)
   return 1;
 }
 
+/* Implementation of linux_target_ops method "supports_hardware_single_step".
+ */
+
+static int
+x86_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 /* This is initialized assuming an amd64 target.
    x86_arch_setup will correct it for i386 or amd64 targets.  */
 
@@ -3298,6 +3307,8 @@ struct linux_target_ops the_low_target =
   x86_emit_ops,
   x86_get_min_fast_tracepoint_insn_len,
   x86_supports_range_stepping,
+  NULL, /* breakpoint_kind_from_current_state */
+  x86_supports_hardware_single_step,
 };
 
 void
diff --git a/gdb/gdbserver/linux-xtensa-low.c b/gdb/gdbserver/linux-xtensa-low.c
index 7c71631..b48e8dd 100644
--- a/gdb/gdbserver/linux-xtensa-low.c
+++ b/gdb/gdbserver/linux-xtensa-low.c
@@ -229,6 +229,14 @@ xtensa_arch_setup (void)
   current_process ()->tdesc = tdesc_xtensa;
 }
 
+/* Support for hardware single step.  */
+
+static int
+xtensa_supports_hardware_single_step (void)
+{
+  return 1;
+}
+
 static const struct regs_info *
 xtensa_regs_info (void)
 {
@@ -248,6 +256,27 @@ struct linux_target_ops the_low_target = {
   NULL,
   0,
   xtensa_breakpoint_at,
+  NULL, /* supports_z_point_type */
+  NULL, /* insert_point */
+  NULL, /* remove_point */
+  NULL, /* stopped_by_watchpoint */
+  NULL, /* stopped_data_address */
+  NULL, /* collect_ptrace_register */
+  NULL, /* supply_ptrace_register */
+  NULL, /* siginfo_fixup */
+  NULL, /* new_process */
+  NULL, /* new_thread */
+  NULL, /* new_fork */
+  NULL, /* prepare_to_resume */
+  NULL, /* process_qsupported */
+  NULL, /* supports_tracepoints */
+  NULL, /* get_thread_area */
+  NULL, /* install_fast_tracepoint_jump_pad */
+  NULL, /* emit_ops */
+  NULL, /* get_min_fast_tracepoint_insn_len */
+  NULL, /* supports_range_stepping */
+  NULL, /* breakpoint_kind_from_current_state */
+  xtensa_supports_hardware_single_step,
 };
 
 
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index 72f18d8..f142489 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -457,6 +457,9 @@ struct target_ops
      PC.  The PCPTR is adjusted to the real memory location in case a flag
      (e.g., the Thumb bit on ARM) is present in the PC.  */
   int (*breakpoint_kind_from_current_state) (CORE_ADDR *pcptr);
+
+  /* Returns true if the target can software single step.  */
+  int (*supports_software_single_step) (void);
 };
 
 extern struct target_ops *the_target;
@@ -649,6 +652,10 @@ int kill_inferior (int);
    ? (*the_target->breakpoint_kind_from_current_state) (pcptr) \
    : target_breakpoint_kind_from_pc (pcptr))
 
+#define target_supports_software_single_step() \
+  (the_target->supports_software_single_step ? \
+   (*the_target->supports_software_single_step) () : 0)
+
 /* Start non-stop mode, returns 0 on success, -1 on failure.   */
 
 int start_non_stop (int nonstop);
-- 
2.6.3