btrace, gdbserver: remove the to_supports_btrace target method

Remove the to_supports_btrace target method and instead rely on detecting errors
when trying to enable recording.  This will also provide a suitable error
message explaining why recording is not possible.

For remote debugging, gdbserver will now always advertise branch tracing related
packets.  When talking to an older GDB, this will cause GDB to try to enable
branch tracing and gdbserver to report a suitable error message every time.

An older gdbserver will not advertise branch tracing related packets if the
one-time check failed, so a newer GDB with this patch will fail to enable branch
tracing at remote_enable_btrace() rather than at btrace_enable().  The error
message is the same in both cases so there should be no user-visible change.

gdb/
	* btrace.c (btrace_enable): Remove target_supports_btrace call.
	* nat/linux-btrace.c (perf_event_pt_event_type): Move.
	(kernel_supports_bts, kernel_supports_pt, linux_supports_bts)
	(linux_supports_pt, linux_supports_btrace): Remove.
	(linux_enable_bts): Call cpu_supports_bts.
	* nat/linux-btrace.h (linux_supports_btrace): Remove.
	* remote.c (remote_supports_btrace): Remove.
	(init_remote_ops): Remove remote_supports_btrace.
	* target-delegates.c: Regenerated.
	* target.c (target_supports_btrace): Remove.
	* target.h (target_ops) <to_supports_btrace>: Remove
	(target_supports_btrace): Remove.
	* x86-linux-nat.c (x86_linux_create_target): Remove
	linux_supports_btrace.

gdbserver/
	* linux-low.c (linux_target_ops): Remove linux_supports_btrace.
	* nto-low.c (nto_target_ops): Remove NULL for supports_btrace.
	* spu-low.c (spu_target_ops): Likewise.
	* win32-low.c (win32_target_ops): Likewise.
	* server.c (supported_btrace_packets): Report packets unconditionally.
	* target.h (target_ops) <supports_btrace>: Remove.
	(target_supports_btrace): Remove.

16 files changed, 51 insertions, 373 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3ff2ccf..df0283a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,22 @@
 2018-02-09  Markus Metzger  <markus.t.metzger@intel.com>
 
+	* btrace.c (btrace_enable): Remove target_supports_btrace call.
+	* nat/linux-btrace.c (perf_event_pt_event_type): Move.
+	(kernel_supports_bts, kernel_supports_pt, linux_supports_bts)
+	(linux_supports_pt, linux_supports_btrace): Remove.
+	(linux_enable_bts): Call cpu_supports_bts.
+	* nat/linux-btrace.h (linux_supports_btrace): Remove.
+	* remote.c (remote_supports_btrace): Remove.
+	(init_remote_ops): Remove remote_supports_btrace.
+	* target-delegates.c: Regenerated.
+	* target.c (target_supports_btrace): Remove.
+	* target.h (target_ops) <to_supports_btrace>: Remove
+	(target_supports_btrace): Remove.
+	* x86-linux-nat.c (x86_linux_create_target): Remove
+	linux_supports_btrace.
+
+2018-02-09  Markus Metzger  <markus.t.metzger@intel.com>
+
 	* nat/linux-btrace.c (linux_enable_btrace): Throw exception if enabling
 	btrace failed.
 	* x86-linux-nat.c (x86_linux_enable_btrace): Catch btrace enabling
diff --git a/gdb/btrace.c b/gdb/btrace.c
index ffcf53a..2b031a4 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1582,9 +1582,6 @@ btrace_enable (struct thread_info *tp, const struct btrace_config *conf)
     error (_("GDB does not support Intel Processor Trace."));
 #endif /* !defined (HAVE_LIBIPT) */
 
-  if (!target_supports_btrace (conf->format))
-    error (_("Target does not support branch tracing."));
-
   DEBUG ("enable thread %s (%s)", print_thread_id (tp),
 	 target_pid_to_str (tp->ptid));
 
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 1b8d6f6..0ff5af7 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,5 +1,15 @@
 2018-02-09  Markus Metzger  <markus.t.metzger@intel.com>
 
+	* linux-low.c (linux_target_ops): Remove linux_supports_btrace.
+	* nto-low.c (nto_target_ops): Remove NULL for supports_btrace.
+	* spu-low.c (spu_target_ops): Likewise.
+	* win32-low.c (win32_target_ops): Likewise.
+	* server.c (supported_btrace_packets): Report packets unconditionally.
+	* target.h (target_ops) <supports_btrace>: Remove.
+	(target_supports_btrace): Remove.
+
+2018-02-09  Markus Metzger  <markus.t.metzger@intel.com>
+
 	* server.c (handle_btrace_enable_bts, handle_btrace_enable_pt)
 	(handle_btrace_disable): Change return type to void.  Use exceptions
 	to report errors.
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index b6b660e..00385ce 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -7531,7 +7531,6 @@ static struct target_ops linux_target_ops = {
   linux_qxfer_libraries_svr4,
   linux_supports_agent,
 #ifdef HAVE_LINUX_BTRACE
-  linux_supports_btrace,
   linux_enable_btrace,
   linux_low_disable_btrace,
   linux_low_read_btrace,
@@ -7541,7 +7540,6 @@ static struct target_ops linux_target_ops = {
   NULL,
   NULL,
   NULL,
-  NULL,
 #endif
   linux_supports_range_stepping,
   linux_proc_pid_to_exec_file,
diff --git a/gdb/gdbserver/nto-low.c b/gdb/gdbserver/nto-low.c
index a570ca9..b68b811 100644
--- a/gdb/gdbserver/nto-low.c
+++ b/gdb/gdbserver/nto-low.c
@@ -991,7 +991,6 @@ static struct target_ops nto_target_ops = {
   NULL, /* get_min_fast_tracepoint_insn_len */
   NULL, /* qxfer_libraries_svr4 */
   NULL, /* support_agent */
-  NULL, /* support_btrace */
   NULL, /* enable_btrace */
   NULL, /* disable_btrace */
   NULL, /* read_btrace */
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 5ce6281..cb02b58 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -2104,27 +2104,10 @@ crc32 (CORE_ADDR base, int len, unsigned int crc)
 static void
 supported_btrace_packets (char *buf)
 {
-  int btrace_supported = 0;
-
-  if (target_supports_btrace (BTRACE_FORMAT_BTS))
-    {
-      strcat (buf, ";Qbtrace:bts+");
-      strcat (buf, ";Qbtrace-conf:bts:size+");
-
-      btrace_supported = 1;
-    }
-
-  if (target_supports_btrace (BTRACE_FORMAT_PT))
-    {
-      strcat (buf, ";Qbtrace:pt+");
-      strcat (buf, ";Qbtrace-conf:pt:size+");
-
-      btrace_supported = 1;
-    }
-
-  if (!btrace_supported)
-    return;
-
+  strcat (buf, ";Qbtrace:bts+");
+  strcat (buf, ";Qbtrace-conf:bts:size+");
+  strcat (buf, ";Qbtrace:pt+");
+  strcat (buf, ";Qbtrace-conf:pt:size+");
   strcat (buf, ";Qbtrace:off+");
   strcat (buf, ";qXfer:btrace:read+");
   strcat (buf, ";qXfer:btrace-conf:read+");
diff --git a/gdb/gdbserver/spu-low.c b/gdb/gdbserver/spu-low.c
index fd1f8d6..5b880d2 100644
--- a/gdb/gdbserver/spu-low.c
+++ b/gdb/gdbserver/spu-low.c
@@ -717,7 +717,6 @@ static struct target_ops spu_target_ops = {
   NULL, /* get_min_fast_tracepoint_insn_len */
   NULL, /* qxfer_libraries_svr4 */
   NULL, /* support_agent */
-  NULL, /* support_btrace */
   NULL, /* enable_btrace */
   NULL, /* disable_btrace */
   NULL, /* read_btrace */
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index 295e64d..dcefe1a 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -391,9 +391,6 @@ struct target_ops
   /* Return true if target supports debugging agent.  */
   int (*supports_agent) (void);
 
-  /* Check whether the target supports branch tracing.  */
-  int (*supports_btrace) (struct target_ops *, enum btrace_format);
-
   /* Enable branch tracing for PTID based on CONF and allocate a branch trace
      target information struct for reading and for disabling branch trace.  */
   struct btrace_target_info *(*enable_btrace)
@@ -623,10 +620,6 @@ int kill_inferior (int);
   (the_target->supports_agent ? \
    (*the_target->supports_agent) () : 0)
 
-#define target_supports_btrace(format)			\
-  (the_target->supports_btrace				\
-   ? (*the_target->supports_btrace) (the_target, format) : 0)
-
 #define target_enable_btrace(ptid, conf) \
   (*the_target->enable_btrace) (ptid, conf)
 
diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index b1d9b51..9f0c4e4 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -1842,7 +1842,6 @@ static struct target_ops win32_target_ops = {
   NULL, /* get_min_fast_tracepoint_insn_len */
   NULL, /* qxfer_libraries_svr4 */
   NULL, /* support_agent */
-  NULL, /* support_btrace */
   NULL, /* enable_btrace */
   NULL, /* disable_btrace */
   NULL, /* read_btrace */
diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index 2b37e41..42f56f9 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -175,23 +175,6 @@ perf_event_read_all (struct perf_event_buffer *pev, gdb_byte **data,
   pev->last_head = data_head;
 }
 
-/* Determine the event type.
-   Returns zero on success and fills in TYPE; returns -1 otherwise.  */
-
-static int
-perf_event_pt_event_type (int *type)
-{
-  gdb_file_up file
-    =  gdb_fopen_cloexec ("/sys/bus/event_source/devices/intel_pt/type", "r");
-  if (file == nullptr)
-    return -1;
-
-  int found = fscanf (file.get (), "%d", type);
-  if (found == 1)
-    return 0;
-  return -1;
-}
-
 /* Try to determine the start address of the Linux kernel.  */
 
 static uint64_t
@@ -376,176 +359,6 @@ perf_event_read_bts (struct btrace_target_info* tinfo, const uint8_t *begin,
   return btrace;
 }
 
-/* Check whether the kernel supports BTS.  */
-
-static int
-kernel_supports_bts (void)
-{
-  struct perf_event_attr attr;
-  pid_t child, pid;
-  int status, file;
-
-  errno = 0;
-  child = fork ();
-  switch (child)
-    {
-    case -1:
-      warning (_("test bts: cannot fork: %s."), safe_strerror (errno));
-      return 0;
-
-    case 0:
-      status = ptrace (PTRACE_TRACEME, 0, NULL, NULL);
-      if (status != 0)
-	{
-	  warning (_("test bts: cannot PTRACE_TRACEME: %s."),
-		   safe_strerror (errno));
-	  _exit (1);
-	}
-
-      status = raise (SIGTRAP);
-      if (status != 0)
-	{
-	  warning (_("test bts: cannot raise SIGTRAP: %s."),
-		   safe_strerror (errno));
-	  _exit (1);
-	}
-
-      _exit (1);
-
-    default:
-      pid = waitpid (child, &status, 0);
-      if (pid != child)
-	{
-	  warning (_("test bts: bad pid %ld, error: %s."),
-		   (long) pid, safe_strerror (errno));
-	  return 0;
-	}
-
-      if (!WIFSTOPPED (status))
-	{
-	  warning (_("test bts: expected stop. status: %d."),
-		   status);
-	  return 0;
-	}
-
-      memset (&attr, 0, sizeof (attr));
-
-      attr.type = PERF_TYPE_HARDWARE;
-      attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS;
-      attr.sample_period = 1;
-      attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR;
-      attr.exclude_kernel = 1;
-      attr.exclude_hv = 1;
-      attr.exclude_idle = 1;
-
-      file = syscall (SYS_perf_event_open, &attr, child, -1, -1, 0);
-      if (file >= 0)
-	close (file);
-
-      kill (child, SIGKILL);
-      ptrace (PTRACE_KILL, child, NULL, NULL);
-
-      pid = waitpid (child, &status, 0);
-      if (pid != child)
-	{
-	  warning (_("test bts: bad pid %ld, error: %s."),
-		   (long) pid, safe_strerror (errno));
-	  if (!WIFSIGNALED (status))
-	    warning (_("test bts: expected killed. status: %d."),
-		     status);
-	}
-
-      return (file >= 0);
-    }
-}
-
-/* Check whether the kernel supports Intel Processor Trace.  */
-
-static int
-kernel_supports_pt (void)
-{
-  struct perf_event_attr attr;
-  pid_t child, pid;
-  int status, file, type;
-
-  errno = 0;
-  child = fork ();
-  switch (child)
-    {
-    case -1:
-      warning (_("test pt: cannot fork: %s."), safe_strerror (errno));
-      return 0;
-
-    case 0:
-      status = ptrace (PTRACE_TRACEME, 0, NULL, NULL);
-      if (status != 0)
-	{
-	  warning (_("test pt: cannot PTRACE_TRACEME: %s."),
-		   safe_strerror (errno));
-	  _exit (1);
-	}
-
-      status = raise (SIGTRAP);
-      if (status != 0)
-	{
-	  warning (_("test pt: cannot raise SIGTRAP: %s."),
-		   safe_strerror (errno));
-	  _exit (1);
-	}
-
-      _exit (1);
-
-    default:
-      pid = waitpid (child, &status, 0);
-      if (pid != child)
-	{
-	  warning (_("test pt: bad pid %ld, error: %s."),
-		   (long) pid, safe_strerror (errno));
-	  return 0;
-	}
-
-      if (!WIFSTOPPED (status))
-	{
-	  warning (_("test pt: expected stop. status: %d."),
-		   status);
-	  return 0;
-	}
-
-      status = perf_event_pt_event_type (&type);
-      if (status != 0)
-	file = -1;
-      else
-	{
-	  memset (&attr, 0, sizeof (attr));
-
-	  attr.size = sizeof (attr);
-	  attr.type = type;
-	  attr.exclude_kernel = 1;
-	  attr.exclude_hv = 1;
-	  attr.exclude_idle = 1;
-
-	  file = syscall (SYS_perf_event_open, &attr, child, -1, -1, 0);
-	  if (file >= 0)
-	    close (file);
-	}
-
-      kill (child, SIGKILL);
-      ptrace (PTRACE_KILL, child, NULL, NULL);
-
-      pid = waitpid (child, &status, 0);
-      if (pid != child)
-	{
-	  warning (_("test pt: bad pid %ld, error: %s."),
-		   (long) pid, safe_strerror (errno));
-	  if (!WIFSIGNALED (status))
-	    warning (_("test pt: expected killed. status: %d."),
-		     status);
-	}
-
-      return (file >= 0);
-    }
-}
-
 /* Check whether an Intel cpu supports BTS.  */
 
 static int
@@ -596,64 +409,6 @@ cpu_supports_bts (void)
     }
 }
 
-/* Check whether the linux target supports BTS.  */
-
-static int
-linux_supports_bts (void)
-{
-  static int cached;
-
-  if (cached == 0)
-    {
-      if (!kernel_supports_bts ())
-	cached = -1;
-      else if (!cpu_supports_bts ())
-	cached = -1;
-      else
-	cached = 1;
-    }
-
-  return cached > 0;
-}
-
-/* Check whether the linux target supports Intel Processor Trace.  */
-
-static int
-linux_supports_pt (void)
-{
-  static int cached;
-
-  if (cached == 0)
-    {
-      if (!kernel_supports_pt ())
-	cached = -1;
-      else
-	cached = 1;
-    }
-
-  return cached > 0;
-}
-
-/* See linux-btrace.h.  */
-
-int
-linux_supports_btrace (struct target_ops *ops, enum btrace_format format)
-{
-  switch (format)
-    {
-    case BTRACE_FORMAT_NONE:
-      return 0;
-
-    case BTRACE_FORMAT_BTS:
-      return linux_supports_bts ();
-
-    case BTRACE_FORMAT_PT:
-      return linux_supports_pt ();
-    }
-
-  internal_error (__FILE__, __LINE__, _("Unknown branch trace format"));
-}
-
 /* Enable branch tracing in BTS format.  */
 
 static struct btrace_target_info *
@@ -664,6 +419,9 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
   __u64 data_offset;
   int pid, pg;
 
+  if (!cpu_supports_bts ())
+    error (_("BTS support has been disabled for the target cpu."));
+
   gdb::unique_xmalloc_ptr<btrace_target_info> tinfo
     (XCNEW (btrace_target_info));
   tinfo->ptid = ptid;
@@ -770,6 +528,23 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
 
 #if defined (PERF_ATTR_SIZE_VER5)
 
+/* Determine the event type.
+   Returns zero on success and fills in TYPE; returns -1 otherwise.  */
+
+static int
+perf_event_pt_event_type (int *type)
+{
+  gdb_file_up file =
+    gdb_fopen_cloexec ("/sys/bus/event_source/devices/intel_pt/type", "r");
+  if (file.get () == nullptr)
+    return -1;
+
+  int found = fscanf (file.get (), "%d", type);
+  if (found == 1)
+    return 0;
+  return -1;
+}
+
 /* Enable branch tracing in Intel Processor Trace format.  */
 
 static struct btrace_target_info *
@@ -1146,14 +921,6 @@ linux_btrace_conf (const struct btrace_target_info *tinfo)
 
 /* See linux-btrace.h.  */
 
-int
-linux_supports_btrace (struct target_ops *ops, enum btrace_format format)
-{
-  return 0;
-}
-
-/* See linux-btrace.h.  */
-
 struct btrace_target_info *
 linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
 {
diff --git a/gdb/nat/linux-btrace.h b/gdb/nat/linux-btrace.h
index 31a8d9e..1180301 100644
--- a/gdb/nat/linux-btrace.h
+++ b/gdb/nat/linux-btrace.h
@@ -103,9 +103,6 @@ struct btrace_target_info
 #endif /* HAVE_LINUX_PERF_EVENT_H */
 };
 
-/* See to_supports_btrace in target.h.  */
-extern int linux_supports_btrace (struct target_ops *, enum btrace_format);
-
 /* See to_enable_btrace in target.h.  */
 extern struct btrace_target_info *
   linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf);
diff --git a/gdb/remote.c b/gdb/remote.c
index b320ee0..e5680f0 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -13095,37 +13095,6 @@ remote_btrace_reset (void)
   memset (&rs->btrace_config, 0, sizeof (rs->btrace_config));
 }
 
-/* Check whether the target supports branch tracing.  */
-
-static int
-remote_supports_btrace (struct target_ops *self, enum btrace_format format)
-{
-  if (packet_support (PACKET_Qbtrace_off) != PACKET_ENABLE)
-    return 0;
-  if (packet_support (PACKET_qXfer_btrace) != PACKET_ENABLE)
-    return 0;
-
-  switch (format)
-    {
-      case BTRACE_FORMAT_NONE:
-	return 0;
-
-      case BTRACE_FORMAT_BTS:
-	return (packet_support (PACKET_Qbtrace_bts) == PACKET_ENABLE);
-
-      case BTRACE_FORMAT_PT:
-	/* The trace is decoded on the host.  Even if our target supports it,
-	   we still need to have libipt to decode the trace.  */
-#if defined (HAVE_LIBIPT)
-	return (packet_support (PACKET_Qbtrace_pt) == PACKET_ENABLE);
-#else /* !defined (HAVE_LIBIPT)  */
-	return 0;
-#endif /* !defined (HAVE_LIBIPT)  */
-    }
-
-  internal_error (__FILE__, __LINE__, _("Unknown branch trace format"));
-}
-
 /* Synchronize the configuration with the target.  */
 
 static void
@@ -13649,7 +13618,6 @@ Specify the serial device it is connected to\n\
   remote_ops.to_traceframe_info = remote_traceframe_info;
   remote_ops.to_use_agent = remote_use_agent;
   remote_ops.to_can_use_agent = remote_can_use_agent;
-  remote_ops.to_supports_btrace = remote_supports_btrace;
   remote_ops.to_enable_btrace = remote_enable_btrace;
   remote_ops.to_disable_btrace = remote_disable_btrace;
   remote_ops.to_teardown_btrace = remote_teardown_btrace;
diff --git a/gdb/target-delegates.c b/gdb/target-delegates.c
index 95ccef4..c7ebdbf 100644
--- a/gdb/target-delegates.c
+++ b/gdb/target-delegates.c
@@ -3458,35 +3458,6 @@ debug_can_use_agent (struct target_ops *self)
   return result;
 }
 
-static int
-delegate_supports_btrace (struct target_ops *self, enum btrace_format arg1)
-{
-  self = self->beneath;
-  return self->to_supports_btrace (self, arg1);
-}
-
-static int
-tdefault_supports_btrace (struct target_ops *self, enum btrace_format arg1)
-{
-  return 0;
-}
-
-static int
-debug_supports_btrace (struct target_ops *self, enum btrace_format arg1)
-{
-  int result;
-  fprintf_unfiltered (gdb_stdlog, "-> %s->to_supports_btrace (...)\n", debug_target.to_shortname);
-  result = debug_target.to_supports_btrace (&debug_target, arg1);
-  fprintf_unfiltered (gdb_stdlog, "<- %s->to_supports_btrace (", debug_target.to_shortname);
-  target_debug_print_struct_target_ops_p (&debug_target);
-  fputs_unfiltered (", ", gdb_stdlog);
-  target_debug_print_enum_btrace_format (arg1);
-  fputs_unfiltered (") = ", gdb_stdlog);
-  target_debug_print_int (result);
-  fputs_unfiltered ("\n", gdb_stdlog);
-  return result;
-}
-
 static struct btrace_target_info *
 delegate_enable_btrace (struct target_ops *self, ptid_t arg1, const struct btrace_config *arg2)
 {
@@ -4458,8 +4429,6 @@ install_delegators (struct target_ops *ops)
     ops->to_use_agent = delegate_use_agent;
   if (ops->to_can_use_agent == NULL)
     ops->to_can_use_agent = delegate_can_use_agent;
-  if (ops->to_supports_btrace == NULL)
-    ops->to_supports_btrace = delegate_supports_btrace;
   if (ops->to_enable_btrace == NULL)
     ops->to_enable_btrace = delegate_enable_btrace;
   if (ops->to_disable_btrace == NULL)
@@ -4647,7 +4616,6 @@ install_dummy_methods (struct target_ops *ops)
   ops->to_traceframe_info = tdefault_traceframe_info;
   ops->to_use_agent = tdefault_use_agent;
   ops->to_can_use_agent = tdefault_can_use_agent;
-  ops->to_supports_btrace = tdefault_supports_btrace;
   ops->to_enable_btrace = tdefault_enable_btrace;
   ops->to_disable_btrace = tdefault_disable_btrace;
   ops->to_teardown_btrace = tdefault_teardown_btrace;
@@ -4808,7 +4776,6 @@ init_debug_target (struct target_ops *ops)
   ops->to_traceframe_info = debug_traceframe_info;
   ops->to_use_agent = debug_use_agent;
   ops->to_can_use_agent = debug_can_use_agent;
-  ops->to_supports_btrace = debug_supports_btrace;
   ops->to_enable_btrace = debug_enable_btrace;
   ops->to_disable_btrace = debug_disable_btrace;
   ops->to_teardown_btrace = debug_teardown_btrace;
diff --git a/gdb/target.c b/gdb/target.c
index ea2ad3f..db7c09b 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -3645,14 +3645,6 @@ target_ranged_break_num_registers (void)
 
 /* See target.h.  */
 
-int
-target_supports_btrace (enum btrace_format format)
-{
-  return current_target.to_supports_btrace (&current_target, format);
-}
-
-/* See target.h.  */
-
 struct btrace_target_info *
 target_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
 {
diff --git a/gdb/target.h b/gdb/target.h
index 096252a..83cf485 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -1110,10 +1110,6 @@ struct target_ops
     int (*to_can_use_agent) (struct target_ops *)
       TARGET_DEFAULT_RETURN (0);
 
-    /* Check whether the target supports branch tracing.  */
-    int (*to_supports_btrace) (struct target_ops *, enum btrace_format)
-      TARGET_DEFAULT_RETURN (0);
-
     /* Enable branch tracing for PTID using CONF configuration.
        Return a branch trace target information struct for reading and for
        disabling branch trace.  */
@@ -2428,9 +2424,6 @@ extern void update_target_permissions (void);
 
 /* Imported from machine dependent code.  */
 
-/* See to_supports_btrace in struct target_ops.  */
-extern int target_supports_btrace (enum btrace_format);
-
 /* See to_enable_btrace in struct target_ops.  */
 extern struct btrace_target_info *
   target_enable_btrace (ptid_t ptid, const struct btrace_config *);
diff --git a/gdb/x86-linux-nat.c b/gdb/x86-linux-nat.c
index 75f68de..a3bdaff 100644
--- a/gdb/x86-linux-nat.c
+++ b/gdb/x86-linux-nat.c
@@ -340,7 +340,6 @@ x86_linux_create_target (void)
   t->to_read_description = x86_linux_read_description;
 
   /* Add btrace methods.  */
-  t->to_supports_btrace = linux_supports_btrace;
   t->to_enable_btrace = x86_linux_enable_btrace;
   t->to_disable_btrace = x86_linux_disable_btrace;
   t->to_teardown_btrace = x86_linux_teardown_btrace;