btrace, gdbserver: use exceptions to convey btrace enable/disable errors

Change error reporting to use exceptions and be prepared to catch them in
gdbserver.  We use the exception message in our error reply to GDB.

This may remove some detail from the error message in the native case since
errno is no longer printed.  Later patches will improve that.

We're still using error strings on the RSP level.  This patch does not affect
the interoperability of older/newer GDB/gdbserver.

gdbserver/
	* server.c (handle_btrace_enable_bts, handle_btrace_enable_pt)
	(handle_btrace_disable): Change return type to void.  Use exceptions
	to report errors.
	(handle_btrace_general_set): Catch exception and copy message to
	return message.

gdb/
	* nat/linux-btrace.c (linux_enable_btrace): Throw exception if enabling
	btrace failed.
	* x86-linux-nat.c (x86_linux_enable_btrace): Catch btrace enabling
	exception and use message in own exception.

gdb/ChangeLog

@@ -1,3 +1,10 @@
+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
+	exception and use message in own exception.
+
 2018-02-09  Markus Metzger  <markus.t.metzger@intel.com>
 
 	* nat/linux-btrace.c: Include scoped_fd.h and scoped_mmap.h.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,11 @@
+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.
+	(handle_btrace_general_set): Catch exception and copy message to
+	return message.
+
 2018-02-08  Tom Tromey  <tom@tromey.com>
 
 	* linux-low.c (install_software_single_step_breakpoints): Use

gdb/gdbserver/server.c

@@ -380,50 +380,41 @@ write_qxfer_response (char *buf, const gdb_byte *data, int len, int is_more)
 
 /* Handle btrace enabling in BTS format.  */
 
-static const char *
+static void
 handle_btrace_enable_bts (struct thread_info *thread)
 {
   if (thread->btrace != NULL)
-    return "E.Btrace already enabled.";
+    error (_("Btrace already enabled."));
 
   current_btrace_conf.format = BTRACE_FORMAT_BTS;
   thread->btrace = target_enable_btrace (thread->id, &current_btrace_conf);
-  if (thread->btrace == NULL)
-    return "E.Could not enable btrace.";
-
-  return NULL;
 }
 
 /* Handle btrace enabling in Intel Processor Trace format.  */
 
-static const char *
+static void
 handle_btrace_enable_pt (struct thread_info *thread)
 {
   if (thread->btrace != NULL)
-    return "E.Btrace already enabled.";
+    error (_("Btrace already enabled."));
 
   current_btrace_conf.format = BTRACE_FORMAT_PT;
   thread->btrace = target_enable_btrace (thread->id, &current_btrace_conf);
-  if (thread->btrace == NULL)
-    return "E.Could not enable btrace.";
-
-  return NULL;
 }
 
 /* Handle btrace disabling.  */
 
-static const char *
+static void
 handle_btrace_disable (struct thread_info *thread)
 {
 
   if (thread->btrace == NULL)
-    return "E.Branch tracing not enabled.";
+    error (_("Branch tracing not enabled."));
 
   if (target_disable_btrace (thread->btrace) != 0)
-    return "E.Could not disable branch tracing.";
+    error (_("Could not disable branch tracing."));
 
   thread->btrace = NULL;
-  return NULL;
 }
 
 /* Handle the "Qbtrace" packet.  */
@@ -432,7 +423,6 @@ static int
 handle_btrace_general_set (char *own_buf)
 {
   struct thread_info *thread;
-  const char *err;
   char *op;
 
   if (!startswith (own_buf, "Qbtrace:"))
@@ -454,21 +444,24 @@ handle_btrace_general_set (char *own_buf)
       return -1;
     }
 
-  err = NULL;
+  TRY
+    {
+      if (strcmp (op, "bts") == 0)
+	handle_btrace_enable_bts (thread);
+      else if (strcmp (op, "pt") == 0)
+	handle_btrace_enable_pt (thread);
+      else if (strcmp (op, "off") == 0)
+	handle_btrace_disable (thread);
+      else
+	error (_("Bad Qbtrace operation.  Use bts, pt, or off."));
 
-  if (strcmp (op, "bts") == 0)
-    err = handle_btrace_enable_bts (thread);
-  else if (strcmp (op, "pt") == 0)
-    err = handle_btrace_enable_pt (thread);
-  else if (strcmp (op, "off") == 0)
-    err = handle_btrace_disable (thread);
-  else
-    err = "E.Bad Qbtrace operation. Use bts, pt, or off.";
-
-  if (err != 0)
-    strcpy (own_buf, err);
-  else
-    write_ok (own_buf);
+      write_ok (own_buf);
+    }
+  CATCH (exception, RETURN_MASK_ERROR)
+    {
+      sprintf (own_buf, "E.%s", exception.message);
+    }
+  END_CATCH
 
   return 1;
 }

gdb/nat/linux-btrace.c

@@ -909,6 +909,9 @@ linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
       break;
     }
 
+  if (tinfo == NULL)
+    error (_("Unknown error."));
+
   return tinfo;
 }
 

gdb/x86-linux-nat.c

@@ -216,14 +216,17 @@ static struct btrace_target_info *
 x86_linux_enable_btrace (struct target_ops *self, ptid_t ptid,
 			 const struct btrace_config *conf)
 {
-  struct btrace_target_info *tinfo;
-
-  errno = 0;
-  tinfo = linux_enable_btrace (ptid, conf);
-
-  if (tinfo == NULL)
-    error (_("Could not enable branch tracing for %s: %s."),
-	   target_pid_to_str (ptid), safe_strerror (errno));
+  struct btrace_target_info *tinfo = nullptr;
+  TRY
+    {
+      tinfo = linux_enable_btrace (ptid, conf);
+    }
+  CATCH (exception, RETURN_MASK_ERROR)
+    {
+      error (_("Could not enable branch tracing for %s: %s"),
+	     target_pid_to_str (ptid), exception.message);
+    }
+  END_CATCH
 
   return tinfo;
 }