gdb: add option to reverse order of _initialize function calls

An earlier patch in this series fixed a dependency problem between two
_initialize functions.  That problem was uncovered by reversing the
order of the initialize function calls.

In short, symtab.c tried to add the alias "maintenance
flush-symbol-cache" for the command "maintenance flush symbol-cache".
Because the "maintenance flush" prefix command was not yet created (it
happens in maint.c, initialized later in this reversed order), the
add_alias_cmd function returned NULL.  That result was passed to
deprecate_cmd, which didn't expected that value, and that caused a
segfault.  This was fixed by changing alias creation functions to take
the target command as a cmd_list_element, instead of by name.

This patch adds a runtime option to reverse the order of the initialize
calls at will.  I chose to use an environment variable for this, over a
parameter (even a "maintenance" one), because:

 - The init functions are called before the early init commands are
   executed, so we could use -iex to turn this mode on early enough.
   This is obvious when you remember that commands / parameters are
   created by initialize funcitions :).

 - This is not something anybody would want to tweak after startup
   anyway.

gdb/ChangeLog:

	* make-init-c: Add option to reverse function calls.

gdb/testsuite/ChangeLog:

	* gdb.base/reverse-init-functions.exp: New.

Change-Id: I543e609cf526e7cb145a006a794d0e6851b63f45

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2021-05-27  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* make-init-c: Add option to reverse function calls.
+
 2021-05-27  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* Makefile.in (INIT_FILES_FILTER_OUT): New.

gdb/make-init-c

@@ -42,6 +42,7 @@ set -e
 echo "/* Do not modify this file.  */"
 echo "/* It is created automatically by the Makefile.  */"
 echo "#include \"defs.h\"      /* For initialize_file_ftype.  */"
+echo "#include <algorithm>"
 echo ""
 sed -n -e 's/^\(_initialize_[a-zA-Z0-9_]*\) ()$/\1/p' "$@" | while read -r name; do
   echo "extern initialize_file_ftype $name;"
@@ -51,7 +52,19 @@ echo "void initialize_all_files ();"
 echo "void"
 echo "initialize_all_files ()"
 echo "{"
+echo "  std::vector<initialize_file_ftype *> functions ="
+echo "    {"
 sed -n -e 's/^\(_initialize_[a-zA-Z0-9_]*\) ()$/\1/p' "$@" | while read -r name; do
-  echo "  $name ();"
+  echo "      $name,"
 done
+echo "    };"
+echo ""
+echo "  /* If GDB_REVERSE_INIT_FUNCTIONS is set (any value), reverse the"
+echo "     order in which initialization functions are called.  This is"
+echo "     used by the testsuite.  */"
+echo "  if (getenv (\"GDB_REVERSE_INIT_FUNCTIONS\") != nullptr)"
+echo "    std::reverse (functions.begin (), functions.end ());"
+echo ""
+echo "  for (initialize_file_ftype *function : functions)"
+echo "    function ();"
 echo "}"

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2021-05-27  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* gdb.base/reverse-init-functions.exp: New.
+
 2021-05-27  Tom de Vries  <tdevries@suse.de>
 
 	PR symtab/27919

gdb/testsuite/gdb.base/reverse-init-functions.exp

@@ -0,0 +1,29 @@
+# Copyright 2020-2021 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 reversing the order of initialize functions calls, during GDB startup.
+#
+# The intent is to catch possible unintended dependencies between two
+# initialize functions, where one depends on the other running before it.
+
+standard_testfile
+
+save_vars { env(GDB_REVERSE_INIT_FUNCTIONS) } {
+    setenv GDB_REVERSE_INIT_FUNCTIONS 1
+    clean_restart
+}
+
+# Verify that GDB has started and is ready to accept commands.
+gdb_test "print 12321" " = 12321"