[PATCH] btrace, gdbserver: check btrace target pointers

[Markus Metzger <markus dot t dot metzger at intel dot com>]

By removing the supports_btrace gdbserver target method we relied on GDB trying
to enable branch tracing and failing on the attempt.

For targets that do not provide the btrace methods, however, an initial request
from GDB for the branch trace configuration to detect whether gdbserver is
already recording resulted in a protocol error.

Have the btrace target methods throw a "Target does not suppor branch tracing"
error and be prepared to handle exceptions in all functions that call btrace
target methods.  We therefore turn the target_* macros into static inline
functions.

Also remove the additional btrace target method checks that resulted in the
above protocol error.

Thanks to Maciej W. Rozycki <macro@mips.com> for reporting this.

2018-02-27  Markus Metzger  <markus.t.metzger@intel.com>

gdbserver/
	* target.h (target_enable_btrace, target_disable_btrace,
	target_read_btrace, target_read_btrace_conf): Turn macro into inline
	function.  Throw error if target method not defined.
	* server.c (handle_qxfer_btrace, handle_qxfer_btrace_conf): Remove
	check for btrace target method.  Be prepared to handle exceptions
	from btrace target methods.
---
 gdb/gdbserver/server.c | 38 ++++++++++++++++++++++++++++----------
 gdb/gdbserver/target.h | 42 ++++++++++++++++++++++++++++++++++--------
 2 files changed, 62 insertions(+), 18 deletions(-)

diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index cb02b58..4fd274f 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -1818,7 +1818,7 @@ handle_qxfer_btrace (const char *annex,
   enum btrace_read_type type;
   int result;
 
-  if (the_target->read_btrace == NULL || writebuf != NULL)
+  if (writebuf != NULL)
     return -2;
 
   if (ptid_equal (general_thread, null_ptid)
@@ -1857,12 +1857,21 @@ handle_qxfer_btrace (const char *annex,
     {
       buffer_free (&cache);
 
-      result = target_read_btrace (thread->btrace, &cache, type);
-      if (result != 0)
+      TRY
 	{
-	  memcpy (own_buf, cache.buffer, cache.used_size);
-	  return -3;
+	  result = target_read_btrace (thread->btrace, &cache, type);
+	  if (result != 0)
+	    memcpy (own_buf, cache.buffer, cache.used_size);
 	}
+      CATCH (exception, RETURN_MASK_ERROR)
+	{
+	  sprintf (own_buf, "E.%s", exception.message);
+	  result = -1;
+	}
+      END_CATCH
+
+      if (result != 0)
+	return -3;
     }
   else if (offset > cache.used_size)
     {
@@ -1889,7 +1898,7 @@ handle_qxfer_btrace_conf (const char *annex,
   struct thread_info *thread;
   int result;
 
-  if (the_target->read_btrace_conf == NULL || writebuf != NULL)
+  if (writebuf != NULL)
     return -2;
 
   if (annex[0] != '\0')
@@ -1919,12 +1928,21 @@ handle_qxfer_btrace_conf (const char *annex,
     {
       buffer_free (&cache);
 
-      result = target_read_btrace_conf (thread->btrace, &cache);
-      if (result != 0)
+      TRY
 	{
-	  memcpy (own_buf, cache.buffer, cache.used_size);
-	  return -3;
+	  result = target_read_btrace_conf (thread->btrace, &cache);
+	  if (result != 0)
+	    memcpy (own_buf, cache.buffer, cache.used_size);
 	}
+      CATCH (exception, RETURN_MASK_ERROR)
+	{
+	  sprintf (own_buf, "E.%s", exception.message);
+	  result = -1;
+	}
+      END_CATCH
+
+      if (result != 0)
+	return -3;
     }
   else if (offset > cache.used_size)
     {
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index dcefe1a..ff38c70 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -620,17 +620,43 @@ int kill_inferior (int);
   (the_target->supports_agent ? \
    (*the_target->supports_agent) () : 0)
 
-#define target_enable_btrace(ptid, conf) \
-  (*the_target->enable_btrace) (ptid, conf)
+static inline struct btrace_target_info *
+target_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
+{
+  if (the_target->enable_btrace == nullptr)
+    error ("Target does not support branch tracing.");
+
+  return (*the_target->enable_btrace) (ptid, conf);
+}
+
+static inline int
+target_disable_btrace (struct btrace_target_info *tinfo)
+{
+  if (the_target->disable_btrace == nullptr)
+    error ("Target does not support branch tracing.");
 
-#define target_disable_btrace(tinfo) \
-  (*the_target->disable_btrace) (tinfo)
+  return (*the_target->disable_btrace) (tinfo);
+}
 
-#define target_read_btrace(tinfo, buffer, type)	\
-  (*the_target->read_btrace) (tinfo, buffer, type)
+static inline int
+target_read_btrace (struct btrace_target_info *tinfo, struct buffer *buffer,
+		    enum btrace_read_type type)
+{
+  if (the_target->read_btrace == nullptr)
+    error ("Target does not support branch tracing.");
+
+  return (*the_target->read_btrace) (tinfo, buffer, type);
+}
+
+static inline int
+target_read_btrace_conf (struct btrace_target_info *tinfo,
+			 struct buffer *buffer)
+{
+  if (the_target->read_btrace_conf == nullptr)
+    error ("Target does not support branch tracing.");
 
-#define target_read_btrace_conf(tinfo, buffer)	\
-  (*the_target->read_btrace_conf) (tinfo, buffer)
+  return (*the_target->read_btrace_conf) (tinfo, buffer);
+}
 
 #define target_supports_range_stepping() \
   (the_target->supports_range_stepping ? \
-- 
1.8.3.1