gdb: startup commands to control Python extension language

Add two new commands to GDB that can be placed into the early
initialization to control how Python starts up.  The new options are:

  set python ignore-environment on|off
  set python dont-write-bytecode auto|on|off

  show python ignore-environment
  show python dont-write-bytecode

These can be used from GDB's startup file to control how the Python
extension language behaves.  These options are equivalent to the -E
and -B flags to python respectively, their descriptions from the
Python man page:

  -E     Ignore environment variables like PYTHONPATH and PYTHONHOME
         that modify the  behavior  of  the  interpreter.

  -B     Don't write .pyc files on import.

gdb/ChangeLog:

	* NEWS: Mention new commands.
	* python/python.c (python_ignore_environment): New static global.
	(show_python_ignore_environment): New function.
	(set_python_ignore_environment): New function.
	(python_dont_write_bytecode): New static global.
	(show_python_dont_write_bytecode): New function.
	(set_python_dont_write_bytecode): New function.
	(_initialize_python): Register new commands.

gdb/doc/ChangeLog:

	* python.texinfo (Python Commands): Mention new commands.

gdb/testsuite/ChangeLog:

	* gdb.python/py-startup-opt.exp: New file.

7 files changed, 289 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4a4fa63..3d266ea 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,16 @@
 2021-04-28  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* NEWS: Mention new commands.
+	* python/python.c (python_ignore_environment): New static global.
+	(show_python_ignore_environment): New function.
+	(set_python_ignore_environment): New function.
+	(python_dont_write_bytecode): New static global.
+	(show_python_dont_write_bytecode): New function.
+	(set_python_dont_write_bytecode): New function.
+	(_initialize_python): Register new commands.
+
+2021-04-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* extension-priv.h (struct extension_language_ops): Rename
 	'finish_initialization' to 'initialize'.
 	* extension.c (finish_ext_lang_initialization): Renamed to...
diff --git a/gdb/NEWS b/gdb/NEWS
index 1cdf19c..6550ea3 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -106,6 +106,22 @@ show print type hex
   When 'on', the 'ptype' command uses hexadecimal notation to print sizes
   and offsets of struct members.  When 'off', decimal notation is used.
 
+set python ignore-environment on|off
+show python ignore-environment
+  When 'on', this causes GDB's builtin Python to ignore any
+  environment variables that would otherwise effect how Python
+  behaves.  This command needs to be added to an early initialization
+  file (e.g. ~/.config/gdb/gdbearlyinit) in order to affect GDB.
+
+set python dont-write-bytecode auto|on|off
+show python dont-write-bytecode
+  When 'on', this causes GDB's builtin Python to not write any
+  byte-code (.pyc files) to disk.  This command needs to be added to
+  an early initialization file (e.g. ~/.config/gdb/gdbearlyinit) in
+  order to affect GDB.  When 'off' byte-code will always be written.
+  When set to 'auto' (the default) Python will check the
+  PYTHONDONTWRITEBYTECODE. environment variable.
+
 * Changed commands
 
 break [PROBE_MODIFIER] [LOCATION] [thread THREADNUM]
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index c22d4a6..e00d0cf 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2021-04-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* python.texinfo (Python Commands): Mention new commands.
+
 2021-04-25  Lancelot Six  <lsix@lancelotsix.com>
 
 	PR gdb/22640
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 9135d41..20d6574 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -103,6 +103,44 @@ controlled using @code{set python print-stack}: if @code{full}, then
 full Python stack printing is enabled; if @code{none}, then Python stack
 and message printing is disabled; if @code{message}, the default, only
 the message component of the error is printed.
+
+@kindex set python ignore-environment
+@item set python ignore-environment @r{[}on@r{|}off@r{]}
+By default this option is @samp{off}, and, when @value{GDBN}
+initializes its internal Python interpreter, the Python interpreter
+will check the environment for variables that will effect how it
+behaves, for example @env{PYTHONHOME}, and
+@env{PYTHONPATH}@footnote{See the ENVIRONMENT VARIABLES section of
+@command{man 1 python} for a comprehensive list.}.
+
+If this option is set to @samp{on} before Python is initialized then
+Python will ignore all such environment variables.  As Python is
+initialized early during @value{GDBN}'s startup process, then this
+option must be placed into the early initialization file
+(@pxref{Initialization Files}) to have the desired effect.
+
+This option is equivalent to passing @option{-E} to the real
+@command{python} executable.
+
+@kindex set python dont-write-bytecode
+@item set python dont-write-bytecode @r{[}auto@r{|}on@r{|}off@r{]}
+When this option is @samp{off}, then, once @value{GDBN} has
+initialized the Python interpreter, the interpreter will byte-compile
+any Python modules that it imports and write the byte code to disk in
+@file{.pyc} files.
+
+If this option is set to @samp{on} before Python is initialized then
+Python will no longer write the byte code to disk.  As Python is
+initialized early during @value{GDBN}'s startup process, then this
+option must be placed into the early initialization file
+(@pxref{Initialization Files}) to have the desired effect.
+
+By default this option is set to @samp{auto}, in this mode Python will
+check the environment variable @env{PYTHONDONTWRITEBYTECODE} to see
+if it should write out byte-code or not.
+
+This option is equivalent to passing @option{-B} to the real
+@command{python} executable.
 @end table
 
 It is also possible to execute a Python script from the @value{GDBN}
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 1d0d86d..c46d68b 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1578,6 +1578,80 @@ python_command (const char *arg, int from_tty)
 
 #endif /* HAVE_PYTHON */
 
+/* When this is turned on before Python is initialised then Python will
+   ignore any environment variables related to Python.  This is equivalent
+   to passing `-E' to the python program.  */
+static bool python_ignore_environment = false;
+
+/* Implement 'show python ignore-environment'.  */
+
+static void
+show_python_ignore_environment (struct ui_file *file, int from_tty,
+				struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Python's ignore-environment setting is %s.\n"),
+		    value);
+}
+
+/* Implement 'set python ignore-environment'.  This sets Python's internal
+   flag no matter when the command is issued, however, if this is used
+   after Py_Initialize has been called then most of the environment will
+   already have been read.  */
+
+static void
+set_python_ignore_environment (const char *args, int from_tty,
+			       struct cmd_list_element *c)
+{
+#ifdef HAVE_PYTHON
+  Py_IgnoreEnvironmentFlag = python_ignore_environment ? 1 : 0;
+#endif
+}
+
+/* When this is turned on before Python is initialised then Python will
+   not write `.pyc' files on import of a module.  */
+static enum auto_boolean python_dont_write_bytecode = AUTO_BOOLEAN_AUTO;
+
+/* Implement 'show python dont-write-bytecode'.  */
+
+static void
+show_python_dont_write_bytecode (struct ui_file *file, int from_tty,
+				 struct cmd_list_element *c, const char *value)
+{
+  if (python_dont_write_bytecode == AUTO_BOOLEAN_AUTO)
+    {
+      const char *auto_string
+	= (python_ignore_environment
+	   || getenv ("PYTHONDONTWRITEBYTECODE") == nullptr) ? "off" : "on";
+
+      fprintf_filtered (file,
+			_("Python's dont-write-bytecode setting is %s (currently %s).\n"),
+			value, auto_string);
+    }
+  else
+    fprintf_filtered (file, _("Python's dont-write-bytecode setting is %s.\n"),
+		      value);
+}
+
+/* Implement 'set python dont-write-bytecode'.  This sets Python's internal
+   flag no matter when the command is issued, however, if this is used
+   after Py_Initialize has been called then many modules could already
+   have been imported and their byte code written out.  */
+
+static void
+set_python_dont_write_bytecode (const char *args, int from_tty,
+				struct cmd_list_element *c)
+{
+#ifdef HAVE_PYTHON
+  if (python_dont_write_bytecode == AUTO_BOOLEAN_AUTO)
+    Py_DontWriteBytecodeFlag
+      = (!python_ignore_environment
+	 && getenv ("PYTHONDONTWRITEBYTECODE") != nullptr) ? 1 : 0;
+  else
+    Py_DontWriteBytecodeFlag
+      = python_dont_write_bytecode == AUTO_BOOLEAN_TRUE ? 1 : 0;
+#endif /* HAVE_PYTHON */
+}
+
 
 
 /* Lists for 'set python' commands.  */
@@ -1880,6 +1954,30 @@ message == an error message without a stack will be printed."),
 			NULL, NULL,
 			&user_set_python_list,
 			&user_show_python_list);
+
+  add_setshow_boolean_cmd ("ignore-environment", no_class,
+			   &python_ignore_environment, _("\
+Set whether the Python interpreter should ignore environment variables."), _(" \
+Show whether the Python interpreter showlist ignore environment variables."), _(" \
+When enabled GDB's Python interpreter will ignore any Python related\n	\
+flags in the environment.  This is equivalent to passing `-E' to a\n	\
+python executable."),
+			   set_python_ignore_environment,
+			   show_python_ignore_environment,
+			   &user_set_python_list,
+			   &user_show_python_list);
+
+  add_setshow_auto_boolean_cmd ("dont-write-bytecode", no_class,
+				&python_dont_write_bytecode, _("\
+Set whether the Python interpreter should ignore environment variables."), _(" \
+Show whether the Python interpreter showlist ignore environment variables."), _(" \
+When enabled GDB's Python interpreter will ignore any Python related\n	\
+flags in the environment.  This is equivalent to passing `-E' to a\n	\
+python executable."),
+				set_python_dont_write_bytecode,
+				show_python_dont_write_bytecode,
+				&user_set_python_list,
+				&user_show_python_list);
 }
 
 #ifdef HAVE_PYTHON
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index d4e02d1..d2ed989 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2021-04-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.python/py-startup-opt.exp: New file.
+
 2021-04-27  Luis Machado  <luis.machado@linaro.org>
 
 	* gdb.base/maint.exp: Drop a pattern that is not needed.
diff --git a/gdb/testsuite/gdb.python/py-startup-opt.exp b/gdb/testsuite/gdb.python/py-startup-opt.exp
new file mode 100644
index 0000000..842add3
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-startup-opt.exp
@@ -0,0 +1,118 @@
+# Copyright 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 the flags within GDB that can be used to control how Python is
+# initialized.
+
+gdb_start
+
+# Skip all tests if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+gdb_exit
+
+# Return a list containing two directory paths for newly created home
+# directories.
+#
+# The first directory is a HOME style home directory, it contains a
+# .gdbearlyinit file containing CONTENT.
+#
+# The second directory is an XDG_CONFIG_HOME style home directory, it
+# contains a sub-directory gdb/, inside which is a file gdbearlyinit
+# that also contains CONTENT.
+#
+# The PREFIX is used in both directory names and should be unique for
+# each call to this function.
+proc setup_home_directories { prefix content } {
+    set home_dir [standard_output_file "${prefix}-home"]
+    set xdg_home_dir [standard_output_file "${prefix}-xdg"]
+
+    file mkdir $home_dir
+    file mkdir "$xdg_home_dir/gdb"
+
+    # Write the content into the HOME directory.
+    set fd [open "$home_dir/.gdbearlyinit" w]
+    puts $fd $content
+    close $fd
+
+    # Copy this from the HOME directory into the XDG_CONFIG_HOME
+    # directory.
+    file copy -force "$home_dir/.gdbearlyinit" "$xdg_home_dir/gdb/gdbearlyinit"
+
+    return [list $home_dir $xdg_home_dir]
+}
+
+# Start GDB and check the status of the Python system flags that we
+# can control from within GDB.
+proc test_python_settings { exp_state } {
+    gdb_start
+
+    gdb_test_no_output "python import sys"
+
+    foreach_with_prefix attr {ignore_environment dont_write_bytecode} {
+	gdb_test_multiline "testname" \
+	    "python" "" \
+	    "if hasattr(sys, 'flags') and getattr(sys.flags, '${attr}', False):" "" \
+	    "  print (\"${attr} is on\")" "" \
+	    "else:" "" \
+	    "  print (\"${attr} is off\")" "" \
+	    "end" "${attr} is ${exp_state}"
+    }
+
+    gdb_exit
+}
+
+save_vars { env(TERM) } {
+    # We need an ANSI-capable terminal to get the output.
+    setenv TERM ansi
+
+    # Check the features are off by default.
+    test_python_settings "off"
+
+    # Create an empty directory we can use as HOME for some of the
+    # tests below.  When we set XDG_CONFIG_HOME we still need to point
+    # HOME at something otherwise GDB complains that it doesn't know
+    # where to create the index cache.
+    set empty_home_dir [standard_output_file fake-empty-home]
+
+    # Create two directories to use for the style setting test.
+    set dirs [setup_home_directories "style" \
+		  [multi_line_input \
+		       "set python dont-write-bytecode on" \
+		       "set python ignore-environment on"]]
+    set home_dir [lindex $dirs 0]
+    set xdg_home_dir [lindex $dirs 1]
+
+    # Now arrange to use the fake home directory early init file.
+    save_vars { INTERNAL_GDBFLAGS env(HOME) env(XDG_CONFIG_HOME) } {
+	set INTERNAL_GDBFLAGS [string map {"-nx" ""} $INTERNAL_GDBFLAGS]
+
+	with_test_prefix "using HOME config" {
+	    # Now test GDB when using the HOME directory.
+	    set env(HOME) $home_dir
+	    unset -nocomplain env(XDG_CONFIG_HOME)
+	    test_python_settings "on"
+	}
+
+	with_test_prefix "using XDG_CONFIG_HOME config" {
+	    # Now test using the XDG_CONFIG_HOME folder.  We still need to
+	    # have a HOME directory set otherwise GDB will issue an error
+	    # about not knowing where to place the index cache.
+	    set env(XDG_CONFIG_HOME) $xdg_home_dir
+	    set env(HOME) $empty_home_dir
+	    test_python_settings "on"
+	}
+    }
+}