gdbserver: Fix crash when QTinit is handled with no inferior process attached

When gdbserver is called with --multi and attach has not been called yet
and tstart is called on the gdb client, gdbserver would crash.
This patch fixes gdbserver so that it returns E01 to the gdb client.

Also this patch adds a testcase to verify this bug named no-attach-trace.exp

gdb/gdbserver/ChangeLog:
	PR breakpoints/15956
	* tracepoint.c (cmd_qtinit): Add check for current_thread.

gdb/testsuite/ChangeLog:
	* gdb.trace/no-attach-trace.c: New file.
	* gdb.trace/no-attach-trace.exp: New file.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,8 @@
+2015-02-10  Antoine Tremblay <antoine.tremblay@ericsson.com>
+
+	PR breakpoints/15956
+	* tracepoint.c (cmd_qtinit): Add check for current_thread.
+
 2015-02-09  Markus Metzger  <markus.t.metzger@intel.com>
 
 	* linux-low.c (linux_low_btrace_conf): Print size.

gdb/gdbserver/tracepoint.c

@@ -2377,6 +2377,13 @@ cmd_qtinit (char *packet)
 {
   struct trace_state_variable *tsv, *prev, *next;
 
+  /* Can't do this command without a pid attached.  */
+  if (current_thread == NULL)
+    {
+      write_enn (packet);
+      return;
+    }
+
   /* Make sure we don't try to read from a trace frame.  */
   current_traceframe = -1;
 

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2015-02-10  Antoine Tremblay <antoine.tremblay@ericsson.com>
+
+	* gdb.trace/no-attach-trace.c: New file.
+	* gdb.trace/no-attach-trace.exp: New file.
+
 2015-02-09  Mark Wielaard  <mjw@redhat.com>
 
 	* gdb.dwarf2/atomic.c: New file.

gdb/testsuite/gdb.trace/Makefile.in

@@ -4,8 +4,8 @@ srcdir = @srcdir@
 .PHONY: all clean mostlyclean distclean realclean
 
 PROGS = actions-changed ax backtrace deltrace disconnected-tracing \
-	infotrace packetlen passc-dyn passcount report save-trace tfile \
-	tfind tracecmd tsv unavailable while-dyn while-stepping
+	infotrace no-attach-trace packetlen passc-dyn passcount report \
+	save-trace tfile tfind tracecmd tsv unavailable while-dyn while-stepping
 
 all info install-info dvi install uninstall installcheck check:
 	@echo "Nothing to be done for $@..."

gdb/testsuite/gdb.trace/no-attach-trace.c

@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2015 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* This program is intended to be a simple dummy program for gdb to read.  */
+
+#include <unistd.h>
+
+int
+main (void)
+{
+  return 0;
+}

gdb/testsuite/gdb.trace/no-attach-trace.exp

@@ -0,0 +1,53 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that trying to trace without a program attached fails properly.
+
+load_lib trace-support.exp
+
+standard_testfile
+
+if {[prepare_for_testing $testfile.exp $testfile $srcfile debug]} {
+    return -1
+}
+
+if ![runto_main] {
+    fail "Can't run to main to check for trace support"
+    return -1
+}
+
+if { ![gdb_target_supports_trace] } then {
+    unsupported "Current target does not support trace"
+    return 1
+
+}
+
+# Clean test state so that we have no process attached.
+clean_restart $testfile
+
+gdb_test "trace main" \
+    "Tracepoint \[0-9\] at.* file .*$srcfile, line.*" \
+    "set tracepoint on main"
+
+gdb_test "tstart" "Target returns error code.*\."
+
+with_test_prefix "after tstart" {
+    if ![runto_main] {
+	fail "Can't run to main, target may have died unexpectedly"
+	return -1
+    }
+}