Implement the ability to set/unset environment variables to GDBserver when starting the inferior

This patch implements the ability to set/unset environment variables
on the remote target, mimicking what GDB already offers to the user.
There are two features present here: user-set and user-unset
environment variables.

User-set environment variables are only the variables that are
explicitly set by the user, using the 'set environment' command.  This
means that variables that were already present in the environment when
starting GDB/GDBserver are not transmitted/considered by this feature.

User-unset environment variables are variables that are explicitly
unset by the user, using the 'unset environment' command.

The idea behind this patch is to store user-set and user-unset
environment variables in two separate sets, both part of gdb_environ.
Then, when extended_remote_create_inferior is preparing to start the
inferior, it will iterate over the two sets and set/unset variables
accordingly.  Three new packets are introduced:

- QEnvironmentHexEncoded, which is used to set environment variables,
  and contains an hex-encoded string in the format "VAR=VALUE" (VALUE
  can be empty if the user set a variable with a null value, by doing
  'set environment VAR=').

- QEnvironmentUnset, which is used to unset environment variables, and
  contains an hex-encoded string in the format "VAR".

- QEnvironmentReset, which is always the first packet to be
  transmitted, and is used to reset the environment, i.e., discard any
  changes made by the user on previous runs.

The QEnvironmentHexEncoded packet is inspired on LLDB's extensions to
the RSP.  Details about it can be seen here:

  <https://raw.githubusercontent.com/llvm-mirror/lldb/master/docs/lldb-gdb-remote.txt>

I decided not to implement the QEnvironment packet because it is
considered deprecated by LLDB.  This packet, on LLDB, serves the same
purpose of QEnvironmentHexEncoded, but sends the information using a
plain text, non-hex-encoded string.

The other two packets are new.

This patch also includes updates to the documentation, testsuite, and
unit tests, without introducing regressions.

gdb/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS (Changes since GDB 8.0): Add entry mentioning new support
	for setting/unsetting environment variables on the remote target.
	(New remote packets): Add entries for QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset.
	* common/environ.c (gdb_environ::operator=): Extend method to
	handle m_user_set_env_list and m_user_unset_env_list.
	(gdb_environ::clear): Likewise.
	(match_var_in_string): Change type of first parameter from 'char
	*' to 'const char *'.
	(gdb_environ::set): Extend method to handle
	m_user_set_env_list and m_user_unset_env_list.
	(gdb_environ::unset): Likewise.
	(gdb_environ::clear_user_set_env): New method.
	(gdb_environ::user_set_envp): Likewise.
	(gdb_environ::user_unset_envp): Likewise.
	* common/environ.h (gdb_environ): Handle m_user_set_env_list and
	m_user_unset_env_list on move constructor/assignment.
	(unset): Add new default parameter 'update_unset_list = true'.
	(clear_user_set_env): New method.
	(user_set_envp): Likewise.
	(user_unset_envp): Likewise.
	(m_user_set_env_list): New std::set.
	(m_user_unset_env_list): Likewise.
	* common/rsp-low.c (hex2str): New function.
	(bin2hex): New overload for bin2hex function.
	* common/rsp-low.c (hex2str): New prototype.
	(str2hex): New overload prototype.
	* remote.c: Include "environ.h". Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset.
	(remote_protocol_features): Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packets.
	(send_environment_packet): New function.
	(extended_remote_environment_support): Likewise.
	(extended_remote_create_inferior): Call
	extended_remote_environment_support.
	(_initialize_remote): Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packet configs.
	* unittests/environ-selftests.c (gdb_selftest_env_var):
	New variable.
	(test_vector_initialization): New function.
	(test_init_from_host_environ): Likewise.
	(test_reinit_from_host_environ): Likewise.
	(test_set_A_unset_B_unset_A_cannot_find_A_can_find_B):
	Likewise.
	(test_unset_set_empty_vector): Likewise.
	(test_vector_clear): Likewise.
	(test_std_move): Likewise.
	(test_move_constructor):
	(test_self_move): Likewise.
	(test_set_unset_reset): Likewise.
	(run_tests): Rewrite in terms of the functions above.

gdb/gdbserver/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* server.c (handle_general_set): Handle QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packets.
	(handle_query): Inform remote that QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset are supported.

gdb/doc/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.texinfo (set environment): Add @anchor.  Explain that
	environment variables set by the user are sent to GDBserver.
	(unset environment): Likewise, but for unsetting variables.
	(Connecting) <Remote Packet>: Add "environment-hex-encoded",
	"QEnvironmentHexEncoded", "environment-unset", "QEnvironmentUnset",
	"environment-reset" and "QEnvironmentReset" to the table.
	(Remote Protocol) <QEnvironmentHexEncoded, QEnvironmentUnset,
	QEnvironmentReset>: New item, explaining the packet.

gdb/testsuite/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.base/share-env-with-gdbserver.c: New file.
	* gdb.base/share-env-with-gdbserver.exp: Likewise.

3 files changed, 300 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index aa1d6b8..c15743b 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* gdb.base/share-env-with-gdbserver.c: New file.
+	* gdb.base/share-env-with-gdbserver.exp: Likewise.
+
 2017-08-28  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* gdb.base/commands.exp (gdbvar_simple_if_test,
diff --git a/gdb/testsuite/gdb.base/share-env-with-gdbserver.c b/gdb/testsuite/gdb.base/share-env-with-gdbserver.c
new file mode 100644
index 0000000..740bd0f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/share-env-with-gdbserver.c
@@ -0,0 +1,40 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2017 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/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Wrapper around getenv for GDB.  */
+
+static const char *
+my_getenv (const char *name)
+{
+  return getenv (name);
+}
+
+int
+main (int argc, char *argv[])
+{
+  const char *myvar = getenv ("GDB_TEST_VAR");
+
+  if (myvar != NULL)
+    printf ("It worked!  myvar = '%s'\n", myvar);
+  else
+    printf ("It failed.");
+
+  return 0;	/* break-here */
+}
diff --git a/gdb/testsuite/gdb.base/share-env-with-gdbserver.exp b/gdb/testsuite/gdb.base/share-env-with-gdbserver.exp
new file mode 100644
index 0000000..7521be1
--- /dev/null
+++ b/gdb/testsuite/gdb.base/share-env-with-gdbserver.exp
@@ -0,0 +1,255 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2017 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 test doesn't make sense on native-gdbserver.
+if { [use_gdb_stub] } {
+    untested "not supported"
+    return
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    return -1
+}
+
+set test_var_name "GDB_TEST_VAR"
+
+# Helper function that performs a check on the output of "getenv".
+#
+# - VAR_NAME is the name of the variable to be checked.
+#
+# - VAR_VALUE is the value expected.
+#
+# - TEST_MSG, if not empty, is the test message to be used by the
+#   "gdb_test".
+#
+# - EMPTY_VAR_P, if non-zero, means that the variable is not expected
+#   to exist.  In this case, VAR_VALUE is not considered.
+
+proc check_getenv { var_name var_value { test_msg "" } { empty_var_p 0 } } {
+    global hex decimal
+
+    if { $test_msg == "" } {
+	set test_msg "print result of getenv for $var_name"
+    }
+
+    if { $empty_var_p } {
+	set var_value_match "0x0"
+    } else {
+	set var_value_match "$hex \"$var_value\""
+    }
+
+    gdb_test "print my_getenv (\"$var_name\")" "\\\$$decimal = $var_value_match" \
+	$test_msg
+}
+
+# Helper function to re-run to main and breaking at the "break-here"
+# label.
+
+proc do_prepare_inferior { } {
+    global decimal hex
+
+    if { ![runto_main] } {
+	return -1
+    }
+
+    gdb_breakpoint [gdb_get_line_number "break-here"]
+
+    gdb_test "continue" "Breakpoint $decimal, main \\\(argc=1, argv=$hex\\\) at.*" \
+	"continue until breakpoint"
+}
+
+# Helper function that does the actual testing.
+#
+# - VAR_VALUE is the value of the environment variable.
+#
+# - VAR_NAME is the name of the environment variable.  If empty,
+#   defaults to $test_var_name.
+#
+# - VAR_NAME_MATCH is the name (regex) that will be used to query the
+#   environment about the variable (via getenv).  This is useful when
+#   we're testing variables with strange names (e.g., with an equal
+#   sign in the name) and we know that the variable will actually be
+#   set using another name.  If empty, defatults, to $var_name.
+#
+# - VAR_VALUE_MATCH is the value (regex) that will be used to match
+#   the result of getenv.  The rationale is the same as explained for
+#   VAR_NAME_MATCH.  If empty, defaults, to $var_value.
+
+proc do_test { var_value { var_name "" } { var_name_match "" } { var_value_match "" } } {
+    global binfile test_var_name
+
+    clean_restart $binfile
+
+    if { $var_name == "" } {
+	set var_name $test_var_name
+    }
+
+    if { $var_name_match == "" } {
+	set var_name_match $var_name
+    }
+
+    if { $var_value_match == "" } {
+	set var_value_match $var_value
+    }
+
+    if { $var_value != "" } {
+	gdb_test_no_output "set environment $var_name = $var_value" \
+	    "set $var_name = $var_value"
+    } else {
+	gdb_test "set environment $var_name =" \
+	    "Setting environment variable \"$var_name\" to null value." \
+	    "set $var_name to null value"
+    }
+
+    do_prepare_inferior
+
+    check_getenv "$var_name_match" "$var_value_match" \
+	"print result of getenv for $var_name"
+}
+
+with_test_prefix "long var value" {
+    do_test "this is my test variable; testing long vars; {}"
+}
+
+with_test_prefix "empty var" {
+    do_test ""
+}
+
+with_test_prefix "strange named var" {
+    # In this test we're doing the following:
+    #
+    #   (gdb) set environment 'asd =' = 123 43; asd b ### [];;;
+    #
+    # However, due to how GDB parses this line, the environment
+    # variable will end up named <'asd> (without the <>), and its
+    # value will be <' = 123 43; asd b ### [];;;> (without the <>).
+    do_test "123 43; asd b ### \[\];;;" "'asd ='" "'asd" \
+	[string_to_regexp "' = 123 43; asd b ### \[\];;;"]
+}
+
+# Test setting and unsetting environment variables in various
+# fashions.
+
+proc test_set_unset_vars { } {
+    global binfile
+
+    clean_restart $binfile
+
+    with_test_prefix "set 3 environment variables" {
+	# Set some environment variables
+	gdb_test_no_output "set environment A = 1" \
+	    "set A to 1"
+	gdb_test_no_output "set environment B = 2" \
+	    "set B to 2"
+	gdb_test_no_output "set environment C = 3" \
+	    "set C to 3"
+
+	do_prepare_inferior
+
+	# Check that the variables are known by the inferior
+	check_getenv "A" "1"
+	check_getenv "B" "2"
+	check_getenv "C" "3"
+    }
+
+    with_test_prefix "unset one variable, reset one" {
+	# Now, unset/reset some values
+	gdb_test_no_output "unset environment A" \
+	    "unset A"
+	gdb_test_no_output "set environment B = 4" \
+	    "set B to 4"
+
+	do_prepare_inferior
+
+	check_getenv "A" "" "" 1
+	check_getenv "B" "4"
+	check_getenv "C" "3"
+    }
+
+    with_test_prefix "unset two variables, reset one" {
+	# Unset more values
+	gdb_test_no_output "unset environment B" \
+	    "unset B"
+	gdb_test_no_output "set environment A = 1" \
+	    "set A to 1 again"
+	gdb_test_no_output "unset environment C" \
+	    "unset C"
+
+	do_prepare_inferior
+
+	check_getenv "A" "1"
+	check_getenv "B" "" "" 1
+	check_getenv "C" "" "" 1
+    }
+}
+
+with_test_prefix "test set/unset of vars" {
+    test_set_unset_vars
+}
+
+# Test that unsetting works.
+
+proc test_unset { } {
+    global hex decimal binfile gdb_prompt
+
+    clean_restart $binfile
+
+    do_prepare_inferior
+
+    set test_msg "check if unset works"
+    set found_home 0
+    gdb_test_multiple "print my_getenv (\"HOME\")" $test_msg {
+	-re "\\\$$decimal = $hex \".*\"\r\n$gdb_prompt $" {
+	    pass $test_msg
+	    set found_home 1
+	}
+	-re "\\\$$decimal = 0x0\r\n$gdb_prompt $" {
+	    untested $test_msg
+	}
+    }
+
+    if { $found_home == 1 } {
+	with_test_prefix "simple unset" {
+	    # We can do the test, because $HOME exists (and therefore can
+	    # be unset).
+	    gdb_test_no_output "unset environment HOME" "unset HOME"
+
+	    do_prepare_inferior
+
+	    # $HOME now must be empty
+	    check_getenv "HOME" "" "" 1
+	}
+
+	with_test_prefix "set-then-unset" {
+	    clean_restart $binfile
+
+	    # Test if setting and then unsetting $HOME works.
+	    gdb_test_no_output "set environment HOME = test" "set HOME as test"
+	    gdb_test_no_output "unset environment HOME" "unset HOME again"
+
+	    do_prepare_inferior
+
+	    check_getenv "HOME" "" "" 1
+	}
+    }
+}
+
+with_test_prefix "test unset of vars" {
+    test_unset
+}