[PATCH] Use -qualified flag when setting temporary breakpoint in start command

[Simon Marchi <simon dot marchi at polymtl dot ca>]

From: Simon Marchi <simon.marchi@efficios.com>

When using the "start" command, GDB puts a temporary breakpoint on the
"main" symbol (we literally invoke the tbreak command).  However, since
it does wild matching by default, it also puts a breakpoint on any C++
method or "main" function in a namespace.  For example, when debugging
GDB, it creates a total of 24 locations:

  (gdb) start
  Temporary breakpoint 1 at 0x198c1e9: main. (24 locations)

as there are a bunch of methods called main in the selftests, such as

  selftests::string_view::capacity_1::main()

If such method was called in the constructor of a global object, or a
function marked with the attribute "constructor", then we would stop at
the wrong place.  Also, this causes a few extra symtabs (those that
contain the "wrong" mains) to be expanded for nothing.

The dummiest, most straightforward solution is to add -qualified when
invoking tbreak.  With this patch, "start" creates a single-location
breakpoint, as expected.

I changed the start.exp test to use a C++ test file, which contains two
main functions.  The test now verifies that the output of "start" is the
output we get when we set a single-location breakpoint.

gdb/ChangeLog:

	* infcmd.c (run_command_1): Pass -qualified to tbreak when usind
	the "start" command.

gdb/testsuite/ChangeLog:

	* gdb.base/start.exp: Change test file to start.cpp.  Enhance
	regexp to match output of single-location breakpoint.
	* gdb.base/start.cpp: New file.
---
 gdb/infcmd.c                     |  5 ++++-
 gdb/testsuite/gdb.base/start.cpp | 31 +++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/start.exp |  4 ++--
 3 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/start.cpp

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index c5977c48a90f..afc59d142649 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -605,7 +605,10 @@ run_command_1 (const char *args, int from_tty, enum run_how run_how)
 
   /* Insert temporary breakpoint in main function if requested.  */
   if (run_how == RUN_STOP_AT_MAIN)
-    tbreak_command (main_name (), 0);
+    {
+      std::string arg = string_printf ("-qualified %s", main_name ());
+      tbreak_command (arg.c_str (), 0);
+    }
 
   exec_file = get_exec_file (0);
 
diff --git a/gdb/testsuite/gdb.base/start.cpp b/gdb/testsuite/gdb.base/start.cpp
new file mode 100644
index 000000000000..2c99bebb454f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/start.cpp
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2019 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/>.  */
+
+namespace foo
+{
+
+int main ()
+{
+  return 1;
+}
+
+} /* namespace foo */
+
+int main()
+{
+  return foo::main ();
+}
diff --git a/gdb/testsuite/gdb.base/start.exp b/gdb/testsuite/gdb.base/start.exp
index d055c9d0d12f..847e322bf379 100644
--- a/gdb/testsuite/gdb.base/start.exp
+++ b/gdb/testsuite/gdb.base/start.exp
@@ -14,7 +14,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
-standard_testfile
+standard_testfile start.cpp
 
 if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
     return -1
@@ -30,5 +30,5 @@ if { [gdb_start_cmd] < 0 } {
 }
 
 gdb_test "" \
-         "main \\(\\) at .*start.c.*" \
+         "Temporary breakpoint $decimal at $hex: file.*main \\(\\) at .*start.cpp:.*" \
          "start"
-- 
2.21.0