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.

gdb/ChangeLog

@@ -1,3 +1,21 @@
+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.
+
 2013-10-23  Pedro Alves  <palves@redhat.com>
 
 	* common/gdb_signals.h (gdb_signal_to_symbol_string): Declare.

gdb/NEWS

@@ -98,6 +98,11 @@ set range-stepping
 show range-stepping
   Control whether target-assisted range stepping is enabled.
 
+set startup-with-shell
+show startup-with-shell
+  Specifies whether Unix child processes are started via a shell or
+  directly.
+
 * You can now use a literal value 'unlimited' for options that
   interpret 0 or -1 as meaning "unlimited".  E.g., "set
   trace-buffer-size unlimited" is now an alias for "set

gdb/config/alpha/nm-osf3.h

@@ -16,10 +16,11 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
-/* Number of traps that happen between exec'ing the shell
+/* Number of traps that happen between exec'ing the shell to run an
-   to run an inferior, and when we finally get to
+   inferior, and when we finally get to the inferior code, not
-   the inferior code.  This is 2 on most implementations.  */
+   counting the exec for the shell.  This is 1 on most
-#define START_INFERIOR_TRAPS_EXPECTED 3
+   implementations.  */
+#define START_INFERIOR_TRAPS_EXPECTED 2
 
 /* Don't trace faults under OSF/1, rely on the posting of the appropriate
    signal if fault tracing is disabled.

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):

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.
+@code{SHELL} environment variable.  If you do not define @code{SHELL},
-@xref{Arguments, ,Your Program's Arguments}.
+@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

gdb/fork-child.c

@@ -150,11 +150,11 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
   if (exec_file == 0)
     exec_file = get_exec_file (1);
 
-  /* STARTUP_WITH_SHELL is defined in inferior.h.  If 0,e we'll just
+  /* 'startup_with_shell' is declared in inferior.h and bound to the
-    do a fork/exec, no shell, so don't bother figuring out what
+     "set startup-with-shell" option.  If 0, we'll just do a
-    shell.  */
+     fork/exec, no shell, so don't bother figuring out what shell.  */
   shell_file = shell_file_arg;
-  if (STARTUP_WITH_SHELL)
+  if (startup_with_shell)
     {
       /* Figure out what shell to start up the user program under.  */
       if (shell_file == NULL)
@@ -419,6 +419,12 @@ startup_inferior (int ntraps)
   int terminal_initted = 0;
   ptid_t resume_ptid;
 
+  if (startup_with_shell)
+    {
+      /* One trap extra for exec'ing the shell.  */
+      pending_execs++;
+    }
+
   if (target_supports_multi_process ())
     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
   else
@@ -533,6 +539,15 @@ unset_exec_wrapper_command (char *args, int from_tty)
   exec_wrapper = NULL;
 }
 
+static void
+show_startup_with_shell (struct ui_file *file, int from_tty,
+			 struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file,
+		    _("Use of shell to start subprocesses is %s.\n"),
+		    value);
+}
+
 /* Provide a prototype to silence -Wmissing-prototypes.  */
 extern initialize_file_ftype _initialize_fork_child;
 
@@ -550,4 +565,12 @@ Show the wrapper for running programs."), NULL,
   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
            _("Disable use of an execution wrapper."),
            &unsetlist);
+
+  add_setshow_boolean_cmd ("startup-with-shell", class_support,
+			   &startup_with_shell, _("\
+Set use of shell to start subprocesses.  The default is on."), _("\
+Show use of shell to start subprocesses."), NULL,
+			   NULL,
+			   show_startup_with_shell,
+			   &setlist, &showlist);
 }

gdb/inf-ptrace.c

@@ -137,9 +137,6 @@ inf_ptrace_create_inferior (struct target_ops *ops,
 
   discard_cleanups (back_to);
 
-  /* START_INFERIOR_TRAPS_EXPECTED is defined in inferior.h, and will
-     be 1 or 2 depending on whether we're starting without or with a
-     shell.  */
   startup_inferior (START_INFERIOR_TRAPS_EXPECTED);
 
   /* On some targets, there must be some explicit actions taken after

gdb/inf-ttrace.c

@@ -642,9 +642,6 @@ inf_ttrace_him (struct target_ops *ops, int pid)
 
   push_target (ops);
 
-  /* START_INFERIOR_TRAPS_EXPECTED is defined in inferior.h, and will
-     be 1 or 2 depending on whether we're starting without or with a
-     shell.  */
   startup_inferior (START_INFERIOR_TRAPS_EXPECTED);
 
   /* On some targets, there must be some explicit actions taken after

gdb/infcmd.c

@@ -147,6 +147,10 @@ enum stop_stack_kind stop_stack_dummy;
 
 int stopped_by_random_signal;
 
+/* See inferior.h.  */
+
+int startup_with_shell = 1;
+
 
 /* Accessor routines.  */
 
@@ -255,7 +259,7 @@ construct_inferior_arguments (int argc, char **argv)
 {
   char *result;
 
-  if (STARTUP_WITH_SHELL)
+  if (startup_with_shell)
     {
 #ifdef __MINGW32__
       /* This holds all the characters considered special to the

gdb/inferior.h

@@ -257,6 +257,25 @@ extern void notice_new_inferior (ptid_t, int, int);
 extern struct value *get_return_value (struct value *function,
                                        struct type *value_type);
 
+/* Whether to start up the debuggee under a shell.
+
+   If startup-with-shell is set, GDB's "run" will attempt to start up
+   the debuggee under a shell.
+
+   This is in order for argument-expansion to occur.  E.g.,
+
+   (gdb) run *
+
+   The "*" gets expanded by the shell into a list of files.
+
+   While this is a nice feature, it may be handy to bypass the shell
+   in some cases.  To disable this feature, do "set startup-with-shell
+   false".
+
+   The catch-exec traps expected during start-up will be one more if
+   the target is started up with a shell.  */
+extern int startup_with_shell;
+
 /* Address at which inferior stopped.  */
 
 extern CORE_ADDR stop_pc;
@@ -346,25 +365,12 @@ struct displaced_step_closure *get_displaced_step_closure_by_addr (CORE_ADDR add
 #define ON_STACK 1
 #define AT_ENTRY_POINT 4
 
-/* If STARTUP_WITH_SHELL is set, GDB's "run"
+/* Number of traps that happen between exec'ing the shell to run an
-   will attempts to start up the debugee under a shell.
+   inferior and when we finally get to the inferior code, not counting
-   This is in order for argument-expansion to occur.  E.g.,
+   the exec for the shell.  This is 1 on most implementations.
-   (gdb) run *
+   Overridden in nm.h files.  */
-   The "*" gets expanded by the shell into a list of files.
-   While this is a nice feature, it turns out to interact badly
-   with some of the catch-fork/catch-exec features we have added.
-   In particular, if the shell does any fork/exec's before
-   the exec of the target program, that can confuse GDB.
-   To disable this feature, set STARTUP_WITH_SHELL to 0.
-   To enable this feature, set STARTUP_WITH_SHELL to 1.
-   The catch-exec traps expected during start-up will
-   be 1 if target is not started up with a shell, 2 if it is.
-   - RT
-   If you disable this, you need to decrement
-   START_INFERIOR_TRAPS_EXPECTED in tm.h.  */
-#define STARTUP_WITH_SHELL 1
 #if !defined(START_INFERIOR_TRAPS_EXPECTED)
-#define START_INFERIOR_TRAPS_EXPECTED	2
+#define START_INFERIOR_TRAPS_EXPECTED	1
 #endif
 
 struct private_inferior;

gdb/procfs.c

@@ -4451,8 +4451,6 @@ procfs_init_inferior (struct target_ops *ops, int pid)
   thread_change_ptid (pid_to_ptid (pid),
 		      ptid_build (pid, lwpid, 0));
 
-  /* Typically two, one trap to exec the shell, one to exec the
-     program being debugged.  Defined by "inferior.h".  */
   startup_inferior (START_INFERIOR_TRAPS_EXPECTED);
 
 #ifdef SYS_syssgi