Make STARTUP_WITH_SHELL a runtime toggle -- add new "set/show startup-with-shell" option.

Occasionaly we hear about people having problems with GDB not being
able to start programs (with "run"/"start").  GDB spawns a shell to
start the program, and most often, it'll be the case that the problem
is actually with the user's shell setup.

GDB has code to disable the use of the shell to start programs.
That's the STARTUP_WITH_SHELL macro that native targets could set to 0
in their nm.h file (though no target actually uses it nowadays).

This patch makes that setting a run-time knob instead.  This will be
useful to quickly diagnose such shell issues, and might also come in
handy at other times (such as when debugging the shell itself, if you
don't have a different shell handy).

gdb/
2013-10-24  Pedro Alves  <palves@redhat.com>

	* NEWS (New options): Mention set/show startup-with-shell.
	* config/alpha/nm-osf3.h (START_INFERIOR_TRAPS_EXPECTED): Set to 2
	instead of 3.
	* fork-child.c (fork_inferior, startup_inferior): Handle 'set
	startup-with-shell'.
	(show_startup_with_shell): New function.
	(_initialize_fork_child): Register the set/show startup-with-shell
	commands.
	* inf-ptrace.c (inf_ptrace_create_inferior): Remove comment.
	* inf-ttrace.c (inf_ttrace_him): Remove comment.
	* procfs.c (procfs_init_inferior): Remove comment.
	* infcmd.c (startup_with_shell): New global.
	* inferior.h (startup_with_shell): Declare global.
	(STARTUP_WITH_SHELL): Delete.
	(START_INFERIOR_TRAPS_EXPECTED): Set to 1 by default instead of 2.

gdb/doc/
2013-10-24  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Starting): Document set/show startup-with-shell.

2 files changed, 34 insertions, 2 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index eb69fdd..c66a152 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2013-10-24  Pedro Alves  <palves@redhat.com>
+
+	* gdb.texinfo (Starting): Document set/show startup-with-shell.
+
 2013-10-11  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.texinfo (Shared Library GDB/MI Catchpoint Commands):
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 44fb174..32516ae 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -2011,8 +2011,10 @@ is used to pass the arguments, so that you may use normal conventions
 (such as wildcard expansion or variable substitution) in describing
 the arguments.
 In Unix systems, you can control which shell is used with the
-@code{SHELL} environment variable.
-@xref{Arguments, ,Your Program's Arguments}.
+@code{SHELL} environment variable.  If you do not define @code{SHELL},
+@value{GDBN} uses the default shell (@file{/bin/sh}).  You can disable
+use of any shell with the @code{set startup-with-shell} command (see
+below for details).
 
 @item The @emph{environment.}
 Your program normally inherits its environment from @value{GDBN}, but you can
@@ -2115,6 +2117,32 @@ environment:
 This command is available when debugging locally on most targets, excluding
 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
 
+@kindex set startup-with-shell
+@item set startup-with-shell
+@itemx set startup-with-shell on
+@itemx set startup-with-shell off
+@itemx show set startup-with-shell
+On Unix systems, by default, if a shell is available on your target,
+@value{GDBN}) uses it to start your program.  Arguments of the
+@code{run} command are passed to the shell, which does variable
+substitution, expands wildcard characters and performs redirection of
+I/O.  In some circumstances, it may be useful to disable such use of a
+shell, for example, when debugging the shell itself or diagnosing
+startup failures such as:
+
+@smallexample
+(@value{GDBP}) run
+Starting program: ./a.out
+During startup program terminated with signal SIGSEGV, Segmentation fault.
+@end smallexample
+
+@noindent
+which indicates the shell or the wrapper specified with
+@samp{exec-wrapper} crashed, not your program.  Most often, this is
+caused by something odd in your shell's initialization file---such as
+@file{.cshrc} for C-shell, $@file{.zshenv} for the Z shell, or the
+file specified in the @samp{BASH_ENV} environment variable for BASH.
+
 @kindex set disable-randomization
 @item set disable-randomization
 @itemx set disable-randomization on