[PATCH v3 6/6] Implement proper "startup-with-shell" support on gdbserver

[Sergio Durigan Junior <sergiodj at redhat dot com>]

This patch implements the proper support for the "startup-with-shell"
feature on gdbserver.  A new packet is added, QStartupWithShell, and
it is sent on initialization.  If the host sends a
"QStartupWithShell:1", it means the inferior shall be started using a
shell.  If the host sends a "QStartupWithShell:0", it means the
inferior shall be started without using a shell.  Any other value is
considered an error.

There is no way to remotely set the shell that will be used by the
target to start the inferior.  In order to do that, the user must
start gdbserver while providing a shell via the $SHELL environment
variable.  The same is true for the host side.

The "set startup-with-shell" setting from the host side is used to
decide whether to start the remote inferior using a shell.  This same
setting is also used to decide whether to use a shell to start the
host inferior; this means that it is not really possible to start the
inferior using different mechanisms on target and host.

A documentation patch is included, along with a new testcase for the
feature.

gdb/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS (Changes since GDB 7.12): Announce that GDBserver is now
	able to start inferiors	using a shell.
	(New remote packets): Announce new packet "QStartupWithShell".
	* remote.c: Add PACKET_QStartupWithShell.
	(remote_start_remote): Handle new PACKET_QStartupWithShell.
	(remote_protocol_features) <QStartupWithShell>: New entry for
	PACKET_QStartupWithShell.
	(_initialize_remote): Call "add_packet_config_cmd" for
	QStartupShell.

gdb/gdbserver/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* server.c (handle_general_set): Handle new packet
	"QStartupWithShell".
	(handle_query): Add "QStartupWithShell" to the list of supported
	packets.
	(gdbserver_usage): Add help text explaining the
	new "--startup-with-shell" and "--no-startup-with-shell" CLI
	options.
	(captured_main): Recognize and act upon the presence of the new
	CLI options.

gdb/testsuite/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.server/startup-with-shell.c: New file.
	* gdb.server/startup-with-shell.exp: Likewise.

gdb/doc/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.texinfo (Starting) <startup-with-shell>: Add @anchor.
	(Connecting) <Remote Packet>: Add "startup-with-shell"
	and "QStartupWithShell" to the table.
	(Remote Protocol) <QStartupWithShell>: New item, explaining the
	packet.
---
 gdb/NEWS                                        | 10 +++
 gdb/doc/gdb.texinfo                             | 31 +++++++++
 gdb/gdbserver/server.c                          | 36 ++++++++++-
 gdb/remote.c                                    | 20 ++++++
 gdb/testsuite/gdb.server/startup-with-shell.c   | 29 +++++++++
 gdb/testsuite/gdb.server/startup-with-shell.exp | 84 +++++++++++++++++++++++++
 6 files changed, 209 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.server/startup-with-shell.c
 create mode 100644 gdb/testsuite/gdb.server/startup-with-shell.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index 21e8cd3..f26e95e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,13 @@
 
 *** Changes since GDB 7.12
 
+* GDBserver is now able to start inferiors using a shell.  When using
+  "target extended-remote", the host GDB honors the value of "set
+  startup-with-shell" in order to inform GDBserver whether the remote
+  inferior should be started with a shell or not.  When using "target
+  remote", it is possible to disable the startup with shell by using
+  the new parameter "--no-startup-with-shell" when starting GDBserver.
+
 * Building GDB and GDBserver now requires a C++11 compiler.
 
   For example, GCC 4.8 or later.
@@ -367,6 +374,9 @@ show max-value-size
 
 * New remote packets
 
+QStartupWithShell
+  Indicates whether the inferior must be started with a shell or not.
+
 exec stop reason
   Indicates that an exec system call was executed.
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index b9b4c82..04688c7 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -2153,6 +2153,7 @@ This command is available when debugging locally on most targets, excluding
 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
 
 @kindex set startup-with-shell
+@anchor{set startup-with-shell}
 @item set startup-with-shell
 @itemx set startup-with-shell on
 @itemx set startup-with-shell off
@@ -20782,6 +20783,10 @@ are:
 @tab @code{QDisableRandomization}
 @tab @code{set disable-randomization}
 
+@item @code{startup-with-shell}
+@tab @code{QStartupWithShell}
+@tab @code{set startup-with-shell}
+
 @item @code{conditional-breakpoints-packet}
 @tab @code{Z0 and Z1}
 @tab @code{Support for target-side breakpoint condition evaluation}
@@ -36362,6 +36367,32 @@ by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
 This should only be done on targets that actually support disabling
 address space randomization.
 
+@item QStartupWithShell:@var{value}
+@cindex startup with shell, remote request
+@cindex @samp{QStartupWithShell} packet
+On UNIX-like targets, it is possible to start the inferior using a
+shell program.  This is the default behavior on both @value{GDBN} and
+@command{gdbserver} (@pxref{set startup-with-shell}).  This packet is
+used to inform @command{gdbserver} whether it should start the
+inferior using a shell or not.
+
+If @var{value} is @var{0}, @command{gdbserver} will not use a shell to
+start the inferior.  If @var{value} is @var{1}, @command{gdbserver}
+will use a shell to start the inferior.  All other values are
+considered an error.
+
+This packet is only available in extended mode (@pxref{extended
+mode}).
+
+Reply:
+@table @samp
+@item OK
+The request succeeded.
+
+@item E @var{nn}
+An error occurred.  The error number @var{nn} is give as hex digits.
+@end table
+
 @item qfThreadInfo
 @itemx qsThreadInfo
 @cindex list active threads, remote request
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 025f7c4..e2c4a30 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -867,6 +867,31 @@ handle_general_set (char *own_buf)
       return;
     }
 
+  if (startswith (own_buf, "QStartupWithShell:"))
+    {
+      char *value = own_buf + strlen ("QStartupWithShell:");
+
+      if (strcmp (value, "1") == 0)
+	startup_with_shell = true;
+      else if (strcmp (value, "0") == 0)
+	startup_with_shell = false;
+      else
+	{
+	  /* Unknown value.  */
+	  fprintf (stderr, "Unknown value to startup-with-shell: %s\n",
+		   own_buf);
+	  write_enn (own_buf);
+	  return;
+	}
+
+      if (remote_debug)
+	debug_printf (_("[Inferior will %s started with shell]"),
+		      startup_with_shell ? "be" : "not be");
+
+      write_ok (own_buf);
+      return;
+    }
+
   /* Otherwise we didn't know what packet it was.  Say we didn't
      understand it.  */
   own_buf[0] = 0;
@@ -2303,7 +2328,7 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 	}
 
       sprintf (own_buf,
-	       "PacketSize=%x;QPassSignals+;QProgramSignals+",
+	       "PacketSize=%x;QPassSignals+;QProgramSignals+;QStartupWithShell+",
 	       PBUFSIZ - 1);
 
       if (target_supports_catch_syscall ())
@@ -3397,6 +3422,11 @@ gdbserver_usage (FILE *stream)
 	   "  --no-disable-randomization\n"
 	   "                        Don't disable address space randomization when\n"
 	   "                        starting PROG.\n"
+	   "  --startup-with-shell\n"
+	   "                        Start PROG using a shell.\n"
+	   "  --no-startup-with-shell\n"
+	   "                        Don't start PROG using a shell (i.e., use the exec*\n"
+	   "                        family of functions).\n"
 	   "\n"
 	   "Debug options:\n"
 	   "\n"
@@ -3680,6 +3710,10 @@ captured_main (int argc, char *argv[])
 	disable_randomization = 1;
       else if (strcmp (*next_arg, "--no-disable-randomization") == 0)
 	disable_randomization = 0;
+      else if (strcmp (*next_arg, "--startup-with-shell") == 0)
+	startup_with_shell = true;
+      else if (strcmp (*next_arg, "--no-startup-with-shell") == 0)
+	startup_with_shell = false;
       else if (strcmp (*next_arg, "--once") == 0)
 	run_once = 1;
       else
diff --git a/gdb/remote.c b/gdb/remote.c
index 3befbd3..4d32a65 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1428,6 +1428,7 @@ enum {
   PACKET_QPassSignals,
   PACKET_QCatchSyscalls,
   PACKET_QProgramSignals,
+  PACKET_QStartupWithShell,
   PACKET_qCRC,
   PACKET_qSearch_memory,
   PACKET_vAttach,
@@ -4079,6 +4080,20 @@ remote_start_remote (int from_tty, struct target_ops *target, int extended_p)
   if (packet_support (PACKET_QAllow) != PACKET_DISABLE)
     remote_set_permissions (target);
 
+  /* If startup-with-shell is on, we inform gdbserver to start the
+     remote inferior using a shell.  */
+  if (packet_support (PACKET_QStartupWithShell) != PACKET_DISABLE)
+    {
+      xsnprintf (rs->buf, get_remote_packet_size (),
+		 "QStartupWithShell:%d", startup_with_shell ? 1 : 0);
+      putpkt (rs->buf);
+      getpkt (&rs->buf, &rs->buf_size, 0);
+      if (strcmp (rs->buf, "OK") != 0)
+	error (_("\
+Remote replied unexpectedly while setting startup-with-shell: %s"),
+	       rs->buf);
+    }
+
   /* gdbserver < 7.7 (before its fix from 2013-12-11) did reply to any
      unknown 'v' packet with string "OK".  "OK" gets interpreted by GDB
      as a reply to known packet.  For packet "vFile:setfs:" it is an
@@ -4633,6 +4648,8 @@ static const struct protocol_feature remote_protocol_features[] = {
     PACKET_QCatchSyscalls },
   { "QProgramSignals", PACKET_DISABLE, remote_supported_packet,
     PACKET_QProgramSignals },
+  { "QStartupWithShell", PACKET_DISABLE, remote_supported_packet,
+    PACKET_QStartupWithShell },
   { "QStartNoAckMode", PACKET_DISABLE, remote_supported_packet,
     PACKET_QStartNoAckMode },
   { "multiprocess", PACKET_DISABLE, remote_supported_packet,
@@ -14117,6 +14134,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_QProgramSignals],
 			 "QProgramSignals", "program-signals", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_QStartupWithShell],
+			 "QStartupWithShell", "startup-with-shell", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_qSymbol],
 			 "qSymbol", "symbol-lookup", 0);
 
diff --git a/gdb/testsuite/gdb.server/startup-with-shell.c b/gdb/testsuite/gdb.server/startup-with-shell.c
new file mode 100644
index 0000000..6278447
--- /dev/null
+++ b/gdb/testsuite/gdb.server/startup-with-shell.c
@@ -0,0 +1,29 @@
+/* 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>
+
+int
+main (int argc, char *argv[])
+{
+  int i;
+
+  for (i = 0; argv[i] != NULL; ++i)
+    printf ("ARG %d = %s\n", i, argv[i]);
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.server/startup-with-shell.exp b/gdb/testsuite/gdb.server/startup-with-shell.exp
new file mode 100644
index 0000000..5630366
--- /dev/null
+++ b/gdb/testsuite/gdb.server/startup-with-shell.exp
@@ -0,0 +1,84 @@
+# 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/>.
+
+# Test startup-with-shell support using extended-remote.
+
+load_lib gdbserver-support.exp
+
+standard_testfile
+
+if { [skip_gdbserver_tests] } {
+    untested "skipping gdbserver tests"
+    return 0
+}
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    return -1
+}
+
+# Initial setup for simple test (wildcard expansion, variable substitution).
+
+proc initial_setup_simple { startup_with_shell run_args } {
+    global hex decimal binfile
+
+    clean_restart $binfile
+    # Make sure we're disconnected, in case we're testing with an
+    # extended-remote board, therefore already connected.
+    gdb_test "disconnect" ".*"
+
+    gdb_test_no_output "set startup-with-shell $startup_with_shell"
+
+    set target_exec [gdbserver_download_current_prog]
+    gdbserver_start_extended
+    gdb_test_no_output "set remote exec-file $target_exec" "set remote exec-file"
+
+    gdb_breakpoint main
+
+    gdb_test "run $run_args" \
+	"Breakpoint ${decimal}, main \\(argc=${decimal}, argv=${hex}\\).*" \
+	"run to main"
+}
+
+## Doing the actual tests
+
+with_test_prefix "startup_with_shell = on; run_args = *.log" {
+    initial_setup_simple "on" "*.log"
+    gdb_test "print argv\[1\]" "\\\$$decimal = $hex \"config\.log\"" \
+	"testing first argument"
+}
+
+with_test_prefix "startup_with_shell = off; run_args = *.log" {
+    initial_setup_simple "off" "*.log"
+    gdb_test "print argv\[1\]" "\\\$$decimal = $hex \"\\\*\.log\"" \
+	"testing first argument"
+}
+
+with_test_prefix "startup_with_shell = on; run_args = \$TEST" {
+    set env(TEST) "1234"
+    initial_setup_simple "on" "\$TEST"
+    gdb_test "print argv\[1\]" "\\\$$decimal = $hex \"1234\"" \
+	"testing first argument"
+    unset env(TEST)
+}
+
+with_test_prefix "startup_with_shell = off; run_args = \$TEST" {
+    set env(TEST) "1234"
+    initial_setup_simple "off" "\$TEST"
+    gdb_test "print argv\[1\]" "\\\$$decimal = $hex \"\\\$TEST\"" \
+	"testing first argument"
+    unset env(TEST)
+}
-- 
2.9.3