Access executable from remote system when first inferior appears

This commit modifies remote_add_inferior to take an extra argument
try_open_exec.  If this is nonzero, remote_add_inferior will attempt
to open this inferior's executable as the main executable if no main
executable is open already.  Callers are updated appropriately.

With this commit, remote debugging can now be initiated using only a
"target remote" or "target extended-remote" command; no "set sysroot"
or "file" commands are required, e.g.

  bash$ gdb -q
  (gdb) target remote | gdbserver - /bin/sh
  Remote debugging using | gdbserver - /bin/sh
  Process /bin/sh created; pid = 32166
  stdin/stdout redirected
  Remote debugging using stdio
  Reading symbols from target:/bin/bash...

One testcase required updating as a result of this commit.  The test
checked that GDB's "info files" command does not crash if no main
executable is open, and relied on GDB's inability to access the main
executable over the remote protocol.  The test was updated to inhibit
this new behavior.

gdb/ChangeLog:

	* remote.c (remote_add_inferior): New argument try_open_exec.
	If nonzero, attempt to open the inferior's executable file as
	the main executable if no main executable is open already.
	All callers updated.
	* NEWS: Mention that GDB now supports automatic location and
	retrieval of executable + files from remote targets.

gdb/doc/ChangeLog:

	* gdb.texinfo (Connecting to a Remote Target): Mention that
	GDB can access program files from remote targets that support
	qXfer:exec-file:read and Host I/O packets.

gdb/testsuite/ChangeLog:

	* gdb.server/server-exec-info.exp: Inhibit GDB from accessing
	the main executable over the remote protocol.

2 files changed, 15 insertions, 4 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 1bb7f41..2335bc1 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,11 @@
 2015-04-17  Gary Benson <gbenson@redhat.com>
 
+	* gdb.texinfo (Connecting to a Remote Target): Mention that
+	GDB can access program files from remote targets that support
+	qXfer:exec-file:read and Host I/O packets.
+
+2015-04-17  Gary Benson <gbenson@redhat.com>
+
 	* gdb.texinfo (Remote Configuration): Document the "set/show
 	remote pid-to-exec-file-packet" command.
 	(General Query Packets): Document the qXfer:exec-file:read
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 964f9c4..0410702 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18952,10 +18952,15 @@ configuration of @value{GDBN}; use @code{help target} to list them.
 @node Connecting
 @section Connecting to a Remote Target
 
-On the @value{GDBN} host machine, you will need an unstripped copy of
-your program, since @value{GDBN} needs symbol and debugging information.
-Start up @value{GDBN} as usual, using the name of the local copy of your
-program as the first argument.
+@value{GDBN} needs an unstripped copy of your program to access symbol
+and debugging information.  Some remote targets (@pxref{qXfer
+executable filename read}, and @pxref{Host I/O Packets}) allow
+@value{GDBN} to access program files over the same connection used to
+communicate with @value{GDBN}.  With such a target, if the remote
+program is unstripped, the only command you need is @code{target
+remote}.  Otherwise, start up @value{GDBN} using the name of the local
+unstripped copy of your program as the first argument, or use the
+@code{file} command.
 
 @cindex @code{target remote}
 @value{GDBN} can communicate with the target over a serial line, or