btrace, gdbserver: check btrace target pointers

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.

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 is 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.

1 files changed, 35 insertions, 8 deletions

diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index dcefe1a..25accd2 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -620,17 +620,44 @@ 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 ? \