Share fork_inferior et al with gdbserver

This is the most important (and the biggest, sorry) patch of the
series.  It moves fork_inferior from gdb/fork-child.c to
nat/fork-inferior.c and makes all the necessary adjustments to both
GDB and gdbserver to make sure everything works OK.

There is no "most important change" with this patch; all changes are
made in a progressive way, making sure that gdbserver had the
necessary features while not breaking GDB at the same time.

I decided to go ahead and implement a partial support for starting the
inferior with a shell on gdbserver, although the full feature comes in
the next patch.  The user won't have the option to disable the
startup-with-shell, and also won't be able to change which shell
gdbserver will use (other than setting the $SHELL environment
variable, that is).

Everything is working as expected, and no regressions were present
during the tests.

gdb/ChangeLog:
2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	* Makefile.in (HFILES_NO_SRCDIR): Add "common/common-inferior.h"
	and "nat/fork-inferior.h".
	* common/common-inferior.h: New file, with contents from
	"gdb/inferior.h".
	* commom/common-utils.c: Include "common-utils.h".
	(stringify_argv): New function.
	* common/common-utils.h (stringify_argv): New prototype.
	* configure.nat: Add "fork-inferior.o" as a dependency for
	"*linux*", "fbsd*" and "nbsd*" hosts.
	* corefile.c (get_exec_file): Update comment.
	* darwin-nat.c (darwin_ptrace_him): Call "gdb_startup_inferior"
	instead of "startup_inferior".
	(darwin_create_inferior): Call "add_thread_silent" after
	"fork_inferior".
	* fork-child.c: Cleanup unnecessary includes.
	(SHELL_FILE): Move to "common/common-fork-child.c".
	(environ): Likewise.
	(exec_wrapper): Initialize.
	(get_exec_wrapper): New function.
	(breakup_args): Move to "common/common-fork-child.c"; rename to
	"breakup_args_for_exec".
	(escape_bang_in_quoted_argument): Move to
	"common/common-fork-child.c".
	(saved_ui): New variable.
	(prefork_hook): New function.
	(postfork_hook): Likewise.
	(postfork_child_hook): Likewise.
	(gdb_startup_inferior): Likewise.
	(fork_inferior): Move to "common/common-fork-child.c".  Update
	function to support gdbserver.
	(startup_inferior): Likewise.
	* gdbcore.h (get_exec_file): Remove declaration.
	* gnu-nat.c (gnu_create_inferior): Call "gdb_startup_inferior"
	instead of "startup_inferior".  Call "add_thread_silent" after
	"fork_inferior".
	* inf-ptrace.c: Include "nat/fork-inferior.h" and "utils.h".
	(inf_ptrace_create_inferior): Call "gdb_startup_inferior"
	instead of "startup_inferior".  Call "add_thread_silent" after
	"fork_inferior".
	* inferior.h: Include "common-inferior.h".
	(trace_start_error): Move to "common/common-utils.h".
	(trace_start_error_with_name): Likewise.
	(fork_inferior): Move prototype to "nat/fork-inferior.h".
	(startup_inferior): Likewise.
	(gdb_startup_inferior): New prototype.
	* nat/fork-inferior.c: New file, with contents from "fork-child.c".
	* nat/fork-inferior.h: New file.
	* procfs.c (procfs_init_inferior): Call "gdb_startup_inferior"
	instead of "startup_inferior".  Call "add_thread_silent" after
	"fork_inferior".
	* target.h (target_terminal_init): Move prototype to
	"target/target.h".
	(target_terminal_inferior): Likewise.
	(target_terminal_ours): Likewise.
	* target/target.h (target_terminal_init): New prototype, moved
	from "target.h".
	(target_terminal_inferior): Likewise.
	(target_terminal_ours): Likewise.
	* utils.c (gdb_flush_out_err): New function.

gdb/gdbserver/ChangeLog:
2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add "nat/fork-inferior.o".
	* configure: Regenerate.
	* configure.srv (srv_linux_obj): Add "fork-child.o" and
	"fork-inferior.o".
	(i[34567]86-*-lynxos*): Likewise.
	(spu*-*-*): Likewise.
	* fork-child.c: New file.
	* linux-low.c: Include "common-inferior.h", "nat/fork-inferior.h"
	and "environ.h".
	(linux_ptrace_fun): New function.
	(linux_create_inferior): Adjust function prototype to reflect
	change on "target.h".  Adjust function code to use
	"fork_inferior".
	(linux_request_interrupt): Delete "signal_pid".
	* lynx-low.c: Include "common-inferior.h" and "nat/fork-inferior.h".
	(lynx_ptrace_fun): New function.
	(lynx_create_inferior): Adjust function prototype to reflect
	change on "target.h".  Adjust function code to use
	"fork_inferior".
	* nto-low.c (nto_create_inferior): Adjust function prototype and
	code to reflect change on "target.h".  Update comments.
	* server.c: Include "common-inferior.h", "nat/fork-inferior.h",
	"common-terminal.h" and "environ.h".
	(terminal_fd): Moved to fork-child.c.
	(old_foreground_pgrp): Likewise.
	(restore_old_foreground_pgrp): Likewise.
	(last_status): Make it global.
	(last_ptid): Likewise.
	(our_environ): New variable.
	(startup_with_shell): Likewise.
	(program_name): Likewise.
	(program_argv): Rename to...
	(program_args): ...this.
	(wrapper_argv): New variable.
	(start_inferior): Delete function.
	(get_exec_wrapper): New function.
	(get_exec_file): Likewise.
	(get_environ): Likewise.
	(prefork_hook): Likewise.
	(post_fork_inferior): Likewise.
	(postfork_hook): Likewise.
	(postfork_child_hook): Likewise.
	(handle_v_run): Update code to deal with arguments coming from the
	remote host.  Update calls from "start_inferior" to
	"create_inferior".
	(captured_main): Likewise.  Initialize environment variable.  Call
	"have_job_control".
	* server.h (post_fork_inferior): New prototype.
	(get_environ): Likewise.
	(last_status): Declare.
	(last_ptid): Likewise.
	(signal_pid): Likewise.
	* spu-low.c: Include "common-inferior.h" and "nat/fork-inferior.h".
	(spu_ptrace_fun): New function.
	(spu_create_inferior): Adjust function prototype to reflect change
	on "target.h".  Adjust function code to use "fork_inferior".
	* target.c (target_terminal_init): New function.
	(target_terminal_inferior): Likewise.
	(target_terminal_ours): Likewise.
	* target.h: Include <vector>.
	(struct target_ops) <create_inferior>: Update prototype.
	(create_inferior): Update macro.
	* utils.c (gdb_flush_out_err): New function.
	* win32-low.c (win32_create_inferior): Adjust function prototype
	and code to reflect change on "target.h".

gdb/testsuite/ChangeLog:
2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.server/non-existing-program.exp: Update regex in order to
	reflect the fact that gdbserver is now using fork_inferior (with a
	shell) to startup the inferior.

1 files changed, 66 insertions, 562 deletions

diff --git a/gdb/fork-child.c b/gdb/fork-child.c
index c1b6f530a43..60985d852dd 100644
--- a/gdb/fork-child.c
+++ b/gdb/fork-child.c
@@ -21,471 +21,64 @@
 
 #include "defs.h"
 #include "inferior.h"
+#include "gdbcmd.h"
 #include "terminal.h"
-#include "target.h"
-#include "gdb_wait.h"
-#include "gdb_vfork.h"
-#include "gdbcore.h"
 #include "gdbthread.h"
-#include "command.h" /* for dont_repeat () */
-#include "gdbcmd.h"
-#include "solib.h"
-#include "filestuff.h"
 #include "top.h"
-#include "signals-state-save-restore.h"
 #include "job-control.h"
-#include <signal.h>
-#include <vector>
-
-/* This just gets used as a default if we can't find SHELL.  */
-#define SHELL_FILE "/bin/sh"
-
-extern char **environ;
-
-static char *exec_wrapper;
-
-/* Build the argument vector for execv(3).  */
-
-class execv_argv
-{
-public:
-  /* EXEC_FILE is the file to run.  ALLARGS is a string containing the
-     arguments to the program.  If starting with a shell, SHELL_FILE
-     is the shell to run.  Otherwise, SHELL_FILE is NULL.  */
-  execv_argv (const char *exec_file, const std::string &allargs,
-	      const char *shell_file);
-
-  /* Return a pointer to the built argv, in the type expected by
-     execv.  The result is (only) valid for as long as this execv_argv
-     object is live.  We return a "char **" because that's the type
-     that the execv functions expect.  Note that it is guaranteed that
-     the execv functions do not modify the argv[] array nor the
-     strings to which the array point.  */
-  char **argv ()
-  {
-    return const_cast<char **> (&m_argv[0]);
-  }
-
-private:
-  /* Disable copying.  */
-  execv_argv (const execv_argv &) = delete;
-  void operator= (const execv_argv &) = delete;
-
-  /* Helper methods for constructing the argument vector.  */
-
-  /* Used when building an argv for a straight execv call, without
-     going via the shell.  */
-  void init_for_no_shell (const char *exec_file,
-			  const std::string &allargs);
-
-  /* Used when building an argv for execing a shell that execs the
-     child program.  */
-  void init_for_shell (const char *exec_file,
-		       const std::string &allargs,
-		       const char *shell_file);
-
-  /* The argument vector built.  Holds non-owning pointers.  Elements
-     either point to the strings passed to the execv_argv ctor, or
-     inside M_STORAGE.  */
-  std::vector<const char *> m_argv;
-
-  /* Storage.  In the no-shell case, this contains a copy of the
-     arguments passed to the ctor, split by '\0'.  In the shell case,
-     this contains the quoted shell command.  I.e., SHELL_COMMAND in
-     {"$SHELL" "-c", SHELL_COMMAND, NULL}.  */
-  std::string m_storage;
-};
-
-/* Create argument vector for straight call to execvp.  Breaks up
-   ALLARGS into an argument vector suitable for passing to execvp and
-   stores it in M_ARGV.  E.g., on "run a b c d" this routine would get
-   as input the string "a b c d", and as output it would fill in
-   M_ARGV with the four arguments "a", "b", "c", "d".  Each argument
-   in M_ARGV points to a substring of a copy of ALLARGS stored in
-   M_STORAGE.  */
-
-void
-execv_argv::init_for_no_shell (const char *exec_file,
-			       const std::string &allargs)
-{
-
-  /* Save/work with a copy stored in our storage.  The pointers pushed
-     to M_ARGV point directly into M_STORAGE, which is modified in
-     place with the necessary NULL terminators.  This avoids N heap
-     allocations and string dups when 1 is sufficient.  */
-  std::string &args_copy = m_storage = allargs;
-
-  m_argv.push_back (exec_file);
-
-  for (size_t cur_pos = 0; cur_pos < args_copy.size ();)
-    {
-      /* Skip whitespace-like chars.  */
-      std::size_t pos = args_copy.find_first_not_of (" \t\n", cur_pos);
-
-      if (pos != std::string::npos)
-	cur_pos = pos;
-
-      /* Find the position of the next separator.  */
-      std::size_t next_sep = args_copy.find_first_of (" \t\n", cur_pos);
-
-      if (next_sep == std::string::npos)
-	{
-	  /* No separator found, which means this is the last
-	     argument.  */
-	  next_sep = args_copy.size ();
-	}
-      else
-	{
-	  /* Replace the separator with a terminator.  */
-	  args_copy[next_sep++] = '\0';
-	}
-
-      m_argv.push_back (&args_copy[cur_pos]);
-
-      cur_pos = next_sep;
-    }
-
-  /* NULL-terminate the vector.  */
-  m_argv.push_back (NULL);
-}
-
-/* When executing a command under the given shell, return true if the
-   '!' character should be escaped when embedded in a quoted
-   command-line argument.  */
-
-static bool
-escape_bang_in_quoted_argument (const char *shell_file)
-{
-  size_t shell_file_len = strlen (shell_file);
-
-  /* Bang should be escaped only in C Shells.  For now, simply check
-     that the shell name ends with 'csh', which covers at least csh
-     and tcsh.  This should be good enough for now.  */
-
-  if (shell_file_len < 3)
-    return false;
+#include "filestuff.h"
+#include "nat/fork-inferior.h"
+#include "common/common-inferior.h"
 
-  if (shell_file[shell_file_len - 3] == 'c'
-      && shell_file[shell_file_len - 2] == 's'
-      && shell_file[shell_file_len - 1] == 'h')
-    return true;
+/* The exec-wrapper, if any, that will be used when starting the
+   inferior.  */
 
-  return false;
-}
+static char *exec_wrapper = NULL;
 
-/* See declaration.  */
+/* See common/common-inferior.h.  */
 
-execv_argv::execv_argv (const char *exec_file,
-			const std::string &allargs,
-			const char *shell_file)
+const char *
+get_exec_wrapper ()
 {
-  if (shell_file == NULL)
-    init_for_no_shell (exec_file, allargs);
-  else
-    init_for_shell (exec_file, allargs, shell_file);
+  return exec_wrapper;
 }
 
-/* See declaration.  */
+/* See nat/fork-inferior.h.  */
 
 void
-execv_argv::init_for_shell (const char *exec_file,
-			    const std::string &allargs,
-			    const char *shell_file)
+gdb_flush_out_err ()
 {
-  /* We're going to call a shell.  */
-  bool escape_bang = escape_bang_in_quoted_argument (shell_file);
-
-  /* We need to build a new shell command string, and make argv point
-     to it.  So build it in the storage.  */
-  std::string &shell_command = m_storage;
-
-  shell_command = "exec ";
-
-  /* Add any exec wrapper.  That may be a program name with arguments,
-     so the user must handle quoting.  */
-  if (exec_wrapper)
-    {
-      shell_command += exec_wrapper;
-      shell_command += ' ';
-    }
-
-  /* Now add exec_file, quoting as necessary.  */
-
-  /* Quoting in this style is said to work with all shells.  But csh
-     on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
-     to.  */
-  bool need_to_quote;
-  const char *p = exec_file;
-  while (1)
-    {
-      switch (*p)
-	{
-	case '\'':
-	case '!':
-	case '"':
-	case '(':
-	case ')':
-	case '$':
-	case '&':
-	case ';':
-	case '<':
-	case '>':
-	case ' ':
-	case '\n':
-	case '\t':
-	  need_to_quote = true;
-	  goto end_scan;
-
-	case '\0':
-	  need_to_quote = false;
-	  goto end_scan;
-
-	default:
-	  break;
-	}
-      ++p;
-    }
- end_scan:
-  if (need_to_quote)
-    {
-      shell_command += '\'';
-      for (p = exec_file; *p != '\0'; ++p)
-	{
-	  if (*p == '\'')
-	    shell_command += "'\\''";
-	  else if (*p == '!' && escape_bang)
-	    shell_command += "\\!";
-	  else
-	    shell_command += *p;
-	}
-      shell_command += '\'';
-    }
-  else
-    shell_command += exec_file;
-
-  shell_command += ' ' + allargs;
-
-  /* If we decided above to start up with a shell, we exec the shell.
-     "-c" says to interpret the next arg as a shell command to
-     execute, and this command is "exec <target-program> <args>".  */
-  m_argv.reserve (4);
-  m_argv.push_back (shell_file);
-  m_argv.push_back ("-c");
-  m_argv.push_back (shell_command.c_str ());
-  m_argv.push_back (NULL);
+  gdb_flush (main_ui->m_gdb_stdout);
+  gdb_flush (main_ui->m_gdb_stderr);
 }
 
-/* See inferior.h.  */
-
-void
-trace_start_error (const char *fmt, ...)
-{
-  va_list ap;
-
-  va_start (ap, fmt);
-  fprintf_unfiltered (gdb_stderr, "Could not trace the inferior "
-		                  "process.\nError: ");
-  vfprintf_unfiltered (gdb_stderr, fmt, ap);
-  va_end (ap);
+/* The ui structure that will be saved on 'prefork_hook' and
+   restored on 'postfork_hook'.  */
+static struct ui *saved_ui = NULL;
 
-  gdb_flush (gdb_stderr);
-  _exit (0177);
-}
-
-/* See inferior.h.  */
+/* See nat/fork-inferior.h.  */
 
 void
-trace_start_error_with_name (const char *string)
+prefork_hook (const char *args)
 {
-  trace_start_error ("%s: %s", string, safe_strerror (errno));
-}
-
-/* Start an inferior Unix child process and sets inferior_ptid to its
-   pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
-   the arguments to the program.  ENV is the environment vector to
-   pass.  SHELL_FILE is the shell file, or NULL if we should pick
-   one.  EXEC_FUN is the exec(2) function to use, or NULL for the default
-   one.  */
-
-/* This function is NOT reentrant.  Some of the variables have been
-   made static to ensure that they survive the vfork call.  */
-
-int
-fork_inferior (const char *exec_file_arg, const std::string &allargs,
-	       char **env, void (*traceme_fun) (void),
-	       void (*init_trace_fun) (int), void (*pre_trace_fun) (void),
-	       char *shell_file_arg,
-               void (*exec_fun)(const char *file, char * const *argv,
-                                char * const *env))
-{
-  int pid;
-  static char default_shell_file[] = SHELL_FILE;
-  /* Set debug_fork then attach to the child while it sleeps, to debug.  */
-  static int debug_fork = 0;
-  /* This is set to the result of setpgrp, which if vforked, will be visible
-     to you in the parent process.  It's only used by humans for debugging.  */
-  static int debug_setpgrp = 657473;
-  static char *shell_file;
-  static const char *exec_file;
-  char **save_our_env;
   const char *inferior_io_terminal = get_inferior_io_terminal ();
-  struct inferior *inf;
-  int i;
-  int save_errno;
-  struct ui *save_ui;
-
-  /* If no exec file handed to us, get it from the exec-file command
-     -- with a good, common error message if none is specified.  */
-  if (exec_file_arg == NULL)
-    exec_file = get_exec_file (1);
-  else
-    exec_file = exec_file_arg;
-
-  /* 'startup_with_shell' is declared in inferior.h and bound to the
-     "set startup-with-shell" option.  If 0, we'll just do a
-     fork/exec, no shell, so don't bother figuring out what shell.  */
-  if (startup_with_shell)
-    {
-      shell_file = shell_file_arg;
-      /* Figure out what shell to start up the user program under.  */
-      if (shell_file == NULL)
-	shell_file = getenv ("SHELL");
-      if (shell_file == NULL)
-	shell_file = default_shell_file;
-    }
-  else
-    shell_file = NULL;
 
-  /* Build the argument vector.  */
-  execv_argv child_argv (exec_file, allargs, shell_file);
-
-  /* Retain a copy of our environment variables, since the child will
-     replace the value of environ and if we're vforked, we have to
-     restore it.  */
-  save_our_env = environ;
-
-  /* Likewise the current UI.  */
-  save_ui = current_ui;
+  gdb_assert (saved_ui == NULL);
+  /* Retain a copy of our UI, since the child will replace this value
+     and if we're vforked, we have to restore it.  */
+  saved_ui = current_ui;
 
   /* Tell the terminal handling subsystem what tty we plan to run on;
      it will just record the information for later.  */
   new_tty_prefork (inferior_io_terminal);
+}
 
-  /* It is generally good practice to flush any possible pending stdio
-     output prior to doing a fork, to avoid the possibility of both
-     the parent and child flushing the same data after the fork.  */
-  gdb_flush (main_ui->m_gdb_stdout);
-  gdb_flush (main_ui->m_gdb_stderr);
-
-  /* If there's any initialization of the target layers that must
-     happen to prepare to handle the child we're about fork, do it
-     now...  */
-  if (pre_trace_fun != NULL)
-    (*pre_trace_fun) ();
-
-  /* Create the child process.  Since the child process is going to
-     exec(3) shortly afterwards, try to reduce the overhead by
-     calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
-     likely that this optimization won't work since there's too much
-     work to do between the vfork(2) and the exec(3).  This is known
-     to be the case on ttrace(2)-based HP-UX, where some handshaking
-     between parent and child needs to happen between fork(2) and
-     exec(2).  However, since the parent is suspended in the vforked
-     state, this doesn't work.  Also note that the vfork(2) call might
-     actually be a call to fork(2) due to the fact that autoconf will
-     ``#define vfork fork'' on certain platforms.  */
-  if (pre_trace_fun || debug_fork)
-    pid = fork ();
-  else
-    pid = vfork ();
-
-  if (pid < 0)
-    perror_with_name (("vfork"));
-
-  if (pid == 0)
-    {
-      /* Switch to the main UI, so that gdb_std{in/out/err} in the
-	 child are mapped to std{in/out/err}.  This makes it possible
-	 to use fprintf_unfiltered/warning/error/etc. in the child
-	 from here on.  */
-      current_ui = main_ui;
-
-      /* Close all file descriptors except those that gdb inherited
-	 (usually 0/1/2), so they don't leak to the inferior.  Note
-	 that this closes the file descriptors of all secondary
-	 UIs.  */
-      close_most_fds ();
-
-      if (debug_fork)
-	sleep (debug_fork);
-
-      /* Create a new session for the inferior process, if necessary.
-         It will also place the inferior in a separate process group.  */
-      if (create_tty_session () <= 0)
-	{
-	  /* No session was created, but we still want to run the inferior
-	     in a separate process group.  */
-	  debug_setpgrp = gdb_setpgid ();
-	  if (debug_setpgrp == -1)
-	    perror (_("setpgrp failed in child"));
-	}
-
-      /* Ask the tty subsystem to switch to the one we specified
-         earlier (or to share the current terminal, if none was
-         specified).  */
-      new_tty ();
-
-      /* Changing the signal handlers for the inferior after
-         a vfork can also change them for the superior, so we don't mess
-         with signals here.  See comments in
-         initialize_signals for how we get the right signal handlers
-         for the inferior.  */
-
-      /* "Trace me, Dr. Memory!"  */
-      (*traceme_fun) ();
-
-      /* The call above set this process (the "child") as debuggable
-        by the original gdb process (the "parent").  Since processes
-        (unlike people) can have only one parent, if you are debugging
-        gdb itself (and your debugger is thus _already_ the
-        controller/parent for this child), code from here on out is
-        undebuggable.  Indeed, you probably got an error message
-        saying "not parent".  Sorry; you'll have to use print
-        statements!  */
-
-      restore_original_signals_state ();
-
-      /* There is no execlpe call, so we have to set the environment
-         for our child in the global variable.  If we've vforked, this
-         clobbers the parent, but environ is restored a few lines down
-         in the parent.  By the way, yes we do need to look down the
-         path to find $SHELL.  Rich Pixley says so, and I agree.  */
-      environ = env;
-
-      char **argv = child_argv.argv ();
-
-      if (exec_fun != NULL)
-        (*exec_fun) (argv[0], &argv[0], env);
-      else
-        execvp (argv[0], &argv[0]);
-
-      /* If we get here, it's an error.  */
-      save_errno = errno;
-      fprintf_unfiltered (gdb_stderr, "Cannot exec %s", argv[0]);
-      for (i = 1; argv[i] != NULL; i++)
-	fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
-      fprintf_unfiltered (gdb_stderr, ".\n");
-      fprintf_unfiltered (gdb_stderr, "Error: %s\n",
-			  safe_strerror (save_errno));
-      gdb_flush (gdb_stderr);
-      _exit (0177);
-    }
-
-  /* Restore our environment in case a vforked child clob'd it.  */
-  environ = save_our_env;
+/* See nat/fork-inferior.h.  */
 
-  /* Likewise the current UI.  */
-  current_ui = save_ui;
+void
+postfork_hook (pid_t pid)
+{
+  struct inferior *inf;
 
   if (!have_inferiors ())
     init_thread_list ();
@@ -494,147 +87,58 @@ fork_inferior (const char *exec_file_arg, const std::string &allargs,
 
   inferior_appeared (inf, pid);
 
-  /* Needed for wait_for_inferior stuff below.  */
+  /* Needed for wait_for_inferior stuff.  */
   inferior_ptid = pid_to_ptid (pid);
 
-  new_tty_postfork ();
+  gdb_assert (saved_ui != NULL);
+  current_ui = saved_ui;
+  saved_ui = NULL;
 
-  /* We have something that executes now.  We'll be running through
-     the shell at this point, but the pid shouldn't change.  Targets
-     supporting MT should fill this task's ptid with more data as soon
-     as they can.  */
-  add_thread_silent (inferior_ptid);
-
-  /* Now that we have a child process, make it our target, and
-     initialize anything target-vector-specific that needs
-     initializing.  */
-  if (init_trace_fun)
-    (*init_trace_fun) (pid);
-
-  /* We are now in the child process of interest, having exec'd the
-     correct program, and are poised at the first instruction of the
-     new program.  */
-  return pid;
+  new_tty_postfork ();
 }
 
-/* Accept NTRAPS traps from the inferior.  */
+/* See nat/fork-inferior.h.  */
 
 void
-startup_inferior (int ntraps)
+postfork_child_hook ()
 {
-  int pending_execs = ntraps;
-  int terminal_initted = 0;
-  ptid_t resume_ptid;
+  /* This is set to the result of setpgrp, which if vforked, will be
+     visible to you in the parent process.  It's only used by humans
+     for debugging.  */
+  static int debug_setpgrp = 657473;
+
+  /* Make sure we switch to main_ui here in order to be able to
+     use the fprintf_unfiltered/warning/error functions.  */
+  current_ui = main_ui;
 
-  if (startup_with_shell)
+  /* Create a new session for the inferior process, if necessary.
+     It will also place the inferior in a separate process group.  */
+  if (create_tty_session () <= 0)
     {
-      /* One trap extra for exec'ing the shell.  */
-      pending_execs++;
+      /* No session was created, but we still want to run the inferior
+	 in a separate process group.  */
+      debug_setpgrp = gdb_setpgid ();
+      if (debug_setpgrp == -1)
+	perror (_("setpgrp failed in child"));
     }
 
-  if (target_supports_multi_process ())
-    resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
-  else
-    resume_ptid = minus_one_ptid;
-
-  /* The process was started by the fork that created it, but it will
-     have stopped one instruction after execing the shell.  Here we
-     must get it up to actual execution of the real program.  */
+  /* Ask the tty subsystem to switch to the one we specified
+     earlier (or to share the current terminal, if none was
+     specified).  */
+  new_tty ();
+}
 
-  if (exec_wrapper)
-    pending_execs++;
+/* See inferior.h.  */
 
-  while (1)
-    {
-      enum gdb_signal resume_signal = GDB_SIGNAL_0;
-      ptid_t event_ptid;
-
-      struct target_waitstatus ws;
-      memset (&ws, 0, sizeof (ws));
-      event_ptid = target_wait (resume_ptid, &ws, 0);
-
-      if (ws.kind == TARGET_WAITKIND_IGNORE)
-	/* The inferior didn't really stop, keep waiting.  */
-	continue;
-
-      switch (ws.kind)
-	{
-	  case TARGET_WAITKIND_SPURIOUS:
-	  case TARGET_WAITKIND_LOADED:
-	  case TARGET_WAITKIND_FORKED:
-	  case TARGET_WAITKIND_VFORKED:
-	  case TARGET_WAITKIND_SYSCALL_ENTRY:
-	  case TARGET_WAITKIND_SYSCALL_RETURN:
-	    /* Ignore gracefully during startup of the inferior.  */
-	    switch_to_thread (event_ptid);
-	    break;
-
-	  case TARGET_WAITKIND_SIGNALLED:
-	    target_terminal_ours ();
-	    target_mourn_inferior (event_ptid);
-	    error (_("During startup program terminated with signal %s, %s."),
-		   gdb_signal_to_name (ws.value.sig),
-		   gdb_signal_to_string (ws.value.sig));
-	    return;
-
-	  case TARGET_WAITKIND_EXITED:
-	    target_terminal_ours ();
-	    target_mourn_inferior (event_ptid);
-	    if (ws.value.integer)
-	      error (_("During startup program exited with code %d."),
-		     ws.value.integer);
-	    else
-	      error (_("During startup program exited normally."));
-	    return;
-
-	  case TARGET_WAITKIND_EXECD:
-	    /* Handle EXEC signals as if they were SIGTRAP signals.  */
-	    xfree (ws.value.execd_pathname);
-	    resume_signal = GDB_SIGNAL_TRAP;
-	    switch_to_thread (event_ptid);
-	    break;
-
-	  case TARGET_WAITKIND_STOPPED:
-	    resume_signal = ws.value.sig;
-	    switch_to_thread (event_ptid);
-	    break;
-	}
-
-      if (resume_signal != GDB_SIGNAL_TRAP)
-	{
-	  /* Let shell child handle its own signals in its own way.  */
-	  target_continue (resume_ptid, resume_signal);
-	}
-      else
-	{
-	  /* We handle SIGTRAP, however; it means child did an exec.  */
-	  if (!terminal_initted)
-	    {
-	      /* Now that the child has exec'd we know it has already
-	         set its process group.  On POSIX systems, tcsetpgrp
-	         will fail with EPERM if we try it before the child's
-	         setpgid.  */
-
-	      /* Set up the "saved terminal modes" of the inferior
-	         based on what modes we are starting it with.  */
-	      target_terminal_init ();
-
-	      /* Install inferior's terminal modes.  */
-	      target_terminal_inferior ();
-
-	      terminal_initted = 1;
-	    }
-
-	  if (--pending_execs == 0)
-	    break;
-
-	  /* Just make it go on.  */
-	  target_continue_no_signal (resume_ptid);
-	}
-    }
+ptid_t
+gdb_startup_inferior (pid_t pid, int num_traps)
+{
+  ptid_t ptid = startup_inferior (pid, num_traps, NULL, NULL);
 
   /* Mark all threads non-executing.  */
-  set_executing (resume_ptid, 0);
+  set_executing (ptid, 0);
+
+  return ptid;
 }
 
 /* Implement the "unset exec-wrapper" command.  */