Implement proper "startup-with-shell" support on gdbserver

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:
2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS (Changes since GDB 8.0): Announce that GDBserver is now
	able to start inferiors	using a shell.
	(New remote packets): Announce new packet "QStartupWithShell".
	* remote.c: Add PACKET_QStartupWithShell.
	(extended_remote_create_inferior): 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:
2017-06-07  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:
2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>

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

gdb/doc/ChangeLog:
2017-06-07  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.

1 files changed, 17 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 112aa2f..8dab5d3 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,20 @@
 
 *** Changes since GDB 8.0
 
+* On Unix systems, GDBserver now does globbing expansion and variable
+  substitution in inferior command line arguments.
+
+  This is done by starting inferiors using a shell, like GDB does.
+  See "set startup-with-shell" in the user manual for how to disable
+  this from GDB when using "target extended-remote".  When using
+  "target remote", you can disable the startup with shell by using the
+  new "--no-startup-with-shell" GDBserver command line option.
+
+* New remote packets
+
+QStartupWithShell
+  Indicates whether the inferior must be started with a shell or not.
+
 *** Changes in GDB 8.0
 
 * GDB now supports access to the PKU register on GNU/Linux. The register is
@@ -409,6 +423,9 @@ 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.