gdb.trace: Read XML target description from tfile.

gdb/ChangeLog:

	* tracefile-tfile.c (trace_tdesc): New static variable.
	(tfile_open): Clear trace_tdesc, call target_find_description.
	(tfile_interp_line): Recognize tdesc lines.
	(tfile_close): Clear trace_tdesc.
	(tfile_xfer_partial_features): New function.
	(tfile_xfer_partial): Call tfile_xfer_partial_features.
	(tfile_append_tdesc_line): New function.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2016-02-10  Marcin Kościelnicki  <koriakin@0x04.net>
+
+	* tracefile-tfile.c (trace_tdesc): New static variable.
+	(tfile_open): Clear trace_tdesc, call target_find_description.
+	(tfile_interp_line): Recognize tdesc lines.
+	(tfile_close): Clear trace_tdesc.
+	(tfile_xfer_partial_features): New function.
+	(tfile_xfer_partial): Call tfile_xfer_partial_features.
+	(tfile_append_tdesc_line): New function.
+
 2016-02-10  Marcin Kościelnicki  <koriakin@0x04.net>
 
 	* ctf.c (ctf_write_tdesc): New function.

gdb/tracefile-tfile.c

@@ -30,6 +30,8 @@
 #include "filenames.h"
 #include "remote.h"
 #include "xml-tdesc.h"
+#include "target-descriptions.h"
+#include "buffer.h"
 
 #ifndef O_LARGEFILE
 #define O_LARGEFILE 0
@@ -391,7 +393,9 @@ static off_t trace_frames_offset;
 static off_t cur_offset;
 static int cur_data_size;
 int trace_regblock_size;
+static struct buffer trace_tdesc;
 
+static void tfile_append_tdesc_line (const char *line);
 static void tfile_interp_line (char *line,
 			       struct uploaded_tp **utpp,
 			       struct uploaded_tsv **utsvp);
@@ -458,6 +462,9 @@ tfile_open (const char *arg, int from_tty)
   trace_filename = xstrdup (filename);
   trace_fd = scratch_chan;
 
+  /* Make sure this is clear.  */
+  buffer_free (&trace_tdesc);
+
   bytes = 0;
   /* Read the file header and test for validity.  */
   tfile_read ((gdb_byte *) &header, TRACE_HEADER_SIZE);
@@ -506,6 +513,9 @@ tfile_open (const char *arg, int from_tty)
 	    error (_("Excessively long lines in trace file"));
 	}
 
+      /* By now, tdesc lines have been read from tfile - let's parse them.  */
+      target_find_description ();
+
       /* Record the starting offset of the binary trace data.  */
       trace_frames_offset = bytes;
 
@@ -569,6 +579,11 @@ tfile_interp_line (char *line, struct uploaded_tp **utpp,
       p += strlen ("tsv ");
       parse_tsv_definition (p, utsvp);
     }
+  else if (startswith (p, "tdesc "))
+    {
+      p += strlen ("tdesc ");
+      tfile_append_tdesc_line (p);
+    }
   else
     warning (_("Ignoring trace file definition \"%s\""), line);
 }
@@ -591,6 +606,7 @@ tfile_close (struct target_ops *self)
   trace_fd = -1;
   xfree (trace_filename);
   trace_filename = NULL;
+  buffer_free (&trace_tdesc);
 
   trace_reset_local_state ();
 }
@@ -876,13 +892,43 @@ tfile_fetch_registers (struct target_ops *ops,
     tracefile_fetch_registers (regcache, regno);
 }
 
+static enum target_xfer_status
+tfile_xfer_partial_features (struct target_ops *ops, const char *annex,
+			     gdb_byte *readbuf, const gdb_byte *writebuf,
+			     ULONGEST offset, ULONGEST len,
+			     ULONGEST *xfered_len)
+{
+  if (strcmp (annex, "target.xml"))
+    return TARGET_XFER_E_IO;
+
+  if (readbuf == NULL)
+    error (_("tfile_xfer_partial: tdesc is read-only"));
+
+  if (trace_tdesc.used_size == 0)
+    return TARGET_XFER_E_IO;
+
+  if (offset >= trace_tdesc.used_size)
+    return TARGET_XFER_EOF;
+
+  if (len > trace_tdesc.used_size - offset)
+    len = trace_tdesc.used_size - offset;
+
+  memcpy (readbuf, trace_tdesc.buffer + offset, len);
+  *xfered_len = len;
+
+  return TARGET_XFER_OK;
+}
+
 static enum target_xfer_status
 tfile_xfer_partial (struct target_ops *ops, enum target_object object,
 		    const char *annex, gdb_byte *readbuf,
 		    const gdb_byte *writebuf, ULONGEST offset, ULONGEST len,
 		    ULONGEST *xfered_len)
 {
-  /* We're only doing regular memory for now.  */
+  /* We're only doing regular memory and tdesc for now.  */
+  if (object == TARGET_OBJECT_AVAILABLE_FEATURES)
+    return tfile_xfer_partial_features (ops, annex, readbuf, writebuf,
+					offset, len, xfered_len);
   if (object != TARGET_OBJECT_MEMORY)
     return TARGET_XFER_E_IO;
 
@@ -1062,6 +1108,16 @@ tfile_traceframe_info (struct target_ops *self)
   return info;
 }
 
+/* Handles tdesc lines from tfile by appending the payload to
+   a global trace_tdesc variable.  */
+
+static void
+tfile_append_tdesc_line (const char *line)
+{
+  buffer_grow_str (&trace_tdesc, line);
+  buffer_grow_str (&trace_tdesc, "\n");
+}
+
 static void
 init_tfile_ops (void)
 {