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Move the multi-forks support to the generic multi-inferiors support.


Hi,

I was mentioning this earlier in the other thread that adds a new command
to allow resuming all threads of all processes, or just of the
current process.  I may have added confusion because I was talking
about this change, while nobody else was seeing it, naturally.  So,
I'm posting it now, in hopes of making things clearer.

The current "multi-forks" support, as implemented by linux-fork.c,
serves as backend for two things.  Staying attached to parent and
child forks simultaneously, and, for checkpoint support.  The former,
is a limited implementation of multi-process/multi-exec.  If one of
the child or parent execs, all hell breaks loose.  It doesn't really
support multi-threaded inferiors.  It bypasses linux-nat.c for killing
and detaching, leaving state inconsistent, and possibly mis-kills or
mis-detaches, etc., etc.  This is what I want to fix.

The checkpoints support however, is a different thing altogether.
The fact that it is implemented using forks for doing the grunt work,
is an implementation detail.  In fact, I believe that the correct
abstraction is for all these checkpoint forks to be associated with
the same inferior id.  When switching between checkpoints, the process
switching should be made transparent to most of GDB and the user (as
already is as possible).  I'm not intersted at this point in improving
the checkpoints implementation to support multi-threaded apps, or
to make it behave if one of the checkpoints does an exec.  However,
I don't want to break it more than it is currently --- it's useful
as is.

So, what I want to do is, to get rid of the linux-fork.c "multi-forks"
support, replace it with generic "multi-inferior" support, but
leave the checkpoint support there.  That is what the patch
below does.

With this in place, it is still possible to debug multiple
forks at once, under the same GDB session.   With a few more patches,
and with the patches I've been posting applied, it will be possible
to follow different execs for each of these forks, all under
the same GDB.  This will allow, for example, the
mythical "gdb /usr/bin/make" -> follow all gcc, ld, as, sed, whatnot
invocations make does until gcc crashes, and catch that SIGSEGV.  So,
as you see, multi-forks is a subset of multi-process/multi-executable
debugging.

While doing this, there are few a commands that don't make sense
to have anymore in a generalized multi-inferior framework.  E.g.,
"info forks" stops making sense if one of the forks has done
an execl...

So, to do this, I'm proposing a few command replacements, similar
to what I've described here:

 http://sourceware.org/gdb/wiki/MultiProcess

|-----------------+-------------------------------------|
| Current command | New command                         |
|-----------------+-------------------------------------|
| delete fork NUM | kill inferior NUM                   |
|-----------------+-------------------------------------|
| detach fork NUM | detach inferior NUM                 |
|-----------------+-------------------------------------|
| restart NUM     | keep, but apply only to checkpoints |
|-----------------+-------------------------------------|
| checkpoint      | keep, adds a new checkpoint.        |
|                 | make followfork child/parent have   |
|                 | no effect on this command (always   |
|                 | follow the parent)                  |
|-----------------+-------------------------------------|
| info forks      | delete, replaced by the             |
|                 | generic "info inferiors"            |
|-----------------+-------------------------------------|
| fork NUM        | delete, replaced by the new generic |
|                 | command 'inferior NUM'              |
|-----------------+-------------------------------------|

Luckily, the multi-forks/checkpoints commands are marked
experimental in GDB.

Note that this even fixes a couple of bugs.  E.g., doing
a checkpoint with "set follow-fork-mode child" was broken
currently.

This applies on top of this other patch,

 http://sourceware.org/ml/gdb-patches/2009-05/msg00650.html

... and has no regressions.

I can now make the linux-nat.c target report multi-process
support to the core of GDB with this (in fact, I have to,
so that it only tries to resume threads of a single-inferior,
since that support is only enabled if the target reports support
for multi-process).

What do you think?  I know multi-inferior/multi-exec/multi-fork
debugging needs better examples in the manual, however, we still
don't have the necessary support to show that off yet.  I'm trying
to push things incrementally without breaking much...

And, I'll need to write a NEWS entry in case this is good
to go, I know.  ;-)

Eli, I hope this clears a few things up.  Michael, CCing you, since
these checkpoints stuff is your baby.

-- 
Pedro Alves

gdb/
2009-05-30  Pedro Alves  <pedro@codesourcery.com>

	* linux-nat.c (linux_child_follow_fork): If we're staying attached
	to the child process, enable event reporting on it.  Don't handle
	checkpoints here.  Instead, add the child fork to the lwp thread
	and inferior lists without clobbering the previous inferior.  Let
	the thread_db layer learn about a new child process, even if
	following the parent.
	(linux_nat_switch_fork): Delete lwps of the current inferior only,
	instead of clearing the whole list.  Use thread_change_ptid to
	give the core the illusion the new checkpoint is still the same
	inferior.  Clear the register cache.
	(linux_handle_extended_wait): Handle checkpoints here.
	(linux_multi_process): Turn on.
	* linux-fork.c (struct fork_info) <pc>: Remove field.
	(init_fork_list): Do not delete the checkpoint from the inferior
	list (it is not there).
	(fork_load_infrun_state): Don't switch inferior_ptid here.  Pass
	the new checkpoint's ptid to linux_nat_switch_fork.
	(fork_save_infrun_state): Make static.  Don't stop the pc field of
	fork_info, it's gone.
	(linux_fork_mourn_inferior): Don't delete the checkpoint from the
	inferior list, it's not there.
	(linux_fork_detach): Ditto.
	(delete_fork_command): Replace mention of fork/checkpoint by
	checkpoint only.
	(detach_fork_command): Likewise.  Don't delete the checkpoint from
	the inferior list.
	(info_forks_command): Adjust.
	(restore_detach_fork): Delete.
	(checkpointing_pid): New.
	(linux_fork_checkpointing_p): New.
	(save_detach_fork): Delete.
	(checkpoint_command): Delete temp_detach_fork.  Don't remove
	breakpoints, that's a nop.  Store the pid of the process we're
	checkpointing, and use make_cleanup_restore_integer to restore it.
	Don't reinsert breakpoints here.
	(process_command, fork_command): Delete.
	(restart_command): Update comments to only mention checkpoints,
	not forks.
	(_initialize_linux_fork): Delete "fork", "process", "info forks"
	commands.
	* linux-fork.h (fork_save_infrun_state, fork_list): Delete
	declarations.
	(linux_fork_checkpointing_p): Declare.
	* cli/cli-cmds.c (killlist): New.
	* cli/cli-cmds.h (killlist): Declare.
	* gdbcmd.h (killlist): Declare.
	* inferior.c: Include "gdbthread.h".
	(detach_inferior_command, kill_inferior_command)
	(inferior_command): New.
	(info_inferiors_command): Allow specifying a specific inferior id.
	(_initialize_inferiors): Register "inferior", "kill inferior" and
	"detach inferior" commands.
	* infcmd.c (_initialize_infcmd): Make "kill" a prefix command.
	* gdbthread.h (any_thread_of_process): Declare.
	* thread.c (any_thread_of_process): New.

gdb/testsuite/
2009-05-30  Pedro Alves  <pedro@codesourcery.com>

	* gdb.base/multi-forks.exp: Only run detach-on-fork tests on
	linux.  Adjust to use "inferior", "info inferiors", "detach
	inferior" and "kill inferior" instead of "restart", "info fork",
	"detach fork" and "delete fork".
	* gdb.base/ending-run.exp: Spell out "info".
	* gdb.base/help.exp: Adjust to use test_prefix_command_help for
	the "kill" command.

gdb/doc/
2009-05-30  Pedro Alves  <pedro@codesourcery.com>

	* gdb.texinfo (Debugging multiple inferiors): Document the
	"inferior", "detach inferior" and "kill inferior" commands.
	(Debugging Programs with Multiple Processes): Adjust to mention
	generic "inferior" commands.  Delete mention of "detach fork" and
	"delete fork".  Cross reference to "Debugging multiple inferiors"
	section.

---
 gdb/cli/cli-cmds.c                     |    4 +
 gdb/cli/cli-cmds.h                     |    4 +
 gdb/doc/gdb.texinfo                    |   88 +++++++++++------------
 gdb/gdbcmd.h                           |    4 +
 gdb/gdbthread.h                        |    3 
 gdb/infcmd.c                           |    5 -
 gdb/inferior.c                         |  120 +++++++++++++++++++++++++++++++-
 gdb/linux-fork.c                       |  123 ++++++---------------------------
 gdb/linux-fork.h                       |    6 -
 gdb/linux-nat.c                        |  106 ++++++++++++++++++++--------
 gdb/testsuite/gdb.base/ending-run.exp  |    2 
 gdb/testsuite/gdb.base/help.exp        |    4 -
 gdb/testsuite/gdb.base/multi-forks.exp |   86 +++++++++++++----------
 gdb/thread.c                           |   12 +++
 14 files changed, 346 insertions(+), 221 deletions(-)

Index: src/gdb/linux-nat.c
===================================================================
--- src.orig/gdb/linux-nat.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/linux-nat.c	2009-05-30 23:13:33.000000000 +0100
@@ -338,6 +338,12 @@ static int stop_callback (struct lwp_inf
 
 static void block_child_signals (sigset_t *prev_mask);
 static void restore_child_signals_mask (sigset_t *prev_mask);
+
+struct lwp_info;
+static struct lwp_info *add_lwp (ptid_t ptid);
+static void purge_lwp_list (int pid);
+static struct lwp_info *find_lwp_pid (ptid_t ptid);
+
 
 /* Trivial list manipulation functions to keep track of a list of
    new stopped processes.  */
@@ -587,6 +593,9 @@ linux_child_follow_fork (struct target_o
     parent_pid = ptid_get_pid (inferior_ptid);
   child_pid = PIDGET (inferior_thread ()->pending_follow.value.related_pid);
 
+  if (!detach_fork)
+    linux_enable_event_reporting (pid_to_ptid (child_pid));
+
   if (! follow_child)
     {
       /* We're already attached to the parent, by default. */
@@ -617,8 +626,9 @@ linux_child_follow_fork (struct target_o
 	}
       else
 	{
-	  struct fork_info *fp;
 	  struct inferior *parent_inf, *child_inf;
+	  struct lwp_info *lp;
+	  struct cleanup *old_chain;
 
 	  /* Add process to GDB's tables.  */
 	  child_inf = add_inferior (child_pid);
@@ -627,11 +637,16 @@ linux_child_follow_fork (struct target_o
 	  child_inf->attach_flag = parent_inf->attach_flag;
 	  copy_terminal_info (child_inf, parent_inf);
 
-	  /* Retain child fork in ptrace (stopped) state.  */
-	  fp = find_fork_pid (child_pid);
-	  if (!fp)
-	    fp = add_fork (child_pid);
-	  fork_save_infrun_state (fp, 0);
+	  old_chain = save_inferior_ptid ();
+
+	  inferior_ptid = ptid_build (child_pid, child_pid, 0);
+	  add_thread (inferior_ptid);
+	  lp = add_lwp (inferior_ptid);
+	  lp->stopped = 1;
+
+	  check_for_thread_db ();
+
+	  do_cleanups (old_chain);
 	}
 
       if (has_vforked)
@@ -692,6 +707,7 @@ linux_child_follow_fork (struct target_o
     {
       struct thread_info *tp;
       struct inferior *parent_inf, *child_inf;
+      struct lwp_info *lp;
 
       /* Before detaching from the parent, remove all breakpoints from it. */
       remove_breakpoints ();
@@ -733,30 +749,33 @@ linux_child_follow_fork (struct target_o
 
       if (has_vforked)
 	{
+	  struct lwp_info *parent_lwp;
+
 	  linux_parent_pid = parent_pid;
+
+	  /* Get rid of the inferior on the core side as well.  */
+	  inferior_ptid = null_ptid;
 	  detach_inferior (parent_pid);
-	}
-      else if (!detach_fork)
-	{
-	  struct fork_info *fp;
-	  /* Retain parent fork in ptrace (stopped) state.  */
-	  fp = find_fork_pid (parent_pid);
-	  if (!fp)
-	    fp = add_fork (parent_pid);
-	  fork_save_infrun_state (fp, 0);
 
-	  /* Also add an entry for the child fork.  */
-	  fp = find_fork_pid (child_pid);
-	  if (!fp)
-	    fp = add_fork (child_pid);
-	  fork_save_infrun_state (fp, 0);
+	  /* Also get rid of all its lwps.  We will detach from this
+	     inferior soon-ish, but, we will still get an exit event
+	     reported through waitpid when it exits.  If we didn't get
+	     rid of the lwps from our list, we would end up reporting
+	     the inferior exit to the core, which would then try to
+	     mourn a non-existing (from the core's perspective)
+	     inferior.  */
+	  parent_lwp = find_lwp_pid (pid_to_ptid (parent_pid));
+	  purge_lwp_list (GET_PID (parent_lwp->ptid));
+	  linux_parent_pid = parent_pid;
 	}
-      else
+      else if (detach_fork)
 	target_detach (NULL, 0);
 
       inferior_ptid = ptid_build (child_pid, child_pid, 0);
+      add_thread (inferior_ptid);
+      lp = add_lwp (inferior_ptid);
+      lp->stopped = 1;
 
-      linux_nat_switch_fork (inferior_ptid);
       check_for_thread_db ();
     }
 
@@ -1073,22 +1092,30 @@ iterate_over_lwps (ptid_t filter,
   return NULL;
 }
 
-/* Update our internal state when changing from one fork (checkpoint,
-   et cetera) to another indicated by NEW_PTID.  We can only switch
-   single-threaded applications, so we only create one new LWP, and
-   the previous list is discarded.  */
+/* Update our internal state when changing from one checkpoint to
+   another indicated by NEW_PTID.  We can only switch single-threaded
+   applications, so we only create one new LWP, and the previous list
+   is discarded.  */
 
 void
 linux_nat_switch_fork (ptid_t new_ptid)
 {
   struct lwp_info *lp;
 
-  init_lwp_list ();
+  purge_lwp_list (GET_PID (inferior_ptid));
+
   lp = add_lwp (new_ptid);
   lp->stopped = 1;
 
-  init_thread_list ();
-  add_thread_silent (new_ptid);
+  /* This changes the thread's ptid while preserving the gdb thread
+     num.  Also changes the inferior pid, while preserving the
+     inferior num.  */
+  thread_change_ptid (inferior_ptid, new_ptid);
+
+  /* We've just told GDB core that the thread changed target id, but,
+     in fact, it really is a different thread, with different register
+     contents.  */
+  registers_changed ();
 }
 
 /* Handle the exit of a single thread LP.  */
@@ -1815,6 +1842,25 @@ linux_handle_extended_wait (struct lwp_i
 
       ourstatus->value.related_pid = ptid_build (new_pid, new_pid, 0);
 
+      if (event == PTRACE_EVENT_FORK
+	  && linux_fork_checkpointing_p (GET_PID (lp->ptid)))
+	{
+	  struct fork_info *fp;
+
+	  /* This won't actually modify the breakpoint list, but will
+	     physically remove the breakpoints from the child.  */
+	  detach_breakpoints (new_pid);
+
+	  /* Retain child fork in ptrace (stopped) state.  */
+	  fp = find_fork_pid (new_pid);
+	  if (!fp)
+	    fp = add_fork (new_pid);
+
+	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  linux_enable_event_reporting (pid_to_ptid (new_pid));
+	  return 0;
+	}
+
       if (event == PTRACE_EVENT_FORK)
 	ourstatus->kind = TARGET_WAITKIND_FORKED;
       else if (event == PTRACE_EVENT_VFORK)
@@ -4289,7 +4335,7 @@ linux_nat_supports_non_stop (void)
 /* True if we want to support multi-process.  To be removed when GDB
    supports multi-exec.  */
 
-int linux_multi_process = 0;
+int linux_multi_process = 1;
 
 static int
 linux_nat_supports_multi_process (void)
Index: src/gdb/linux-fork.c
===================================================================
--- src.orig/gdb/linux-fork.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/linux-fork.c	2009-05-30 23:03:52.000000000 +0100
@@ -27,6 +27,7 @@
 #include "gdb_string.h"
 #include "linux-fork.h"
 #include "linux-nat.h"
+#include "gdbthread.h"
 
 #include <sys/ptrace.h>
 #include "gdb_wait.h"
@@ -52,7 +53,6 @@ struct fork_info
   struct regcache *savedregs;	/* Convenient for info fork, saves 
 				   having to actually switch contexts.  */
   int clobber_regs;		/* True if we should restore saved regs.  */
-  ULONGEST pc;			/* PC for info fork.  */
   off_t *filepos;		/* Set of open file descriptors' offsets.  */
   int maxfd;
 };
@@ -210,7 +210,6 @@ init_fork_list (void)
   for (fp = fork_list; fp; fp = fpnext)
     {
       fpnext = fp->next;
-      delete_inferior (ptid_get_pid (fp->ptid));
       free_fork (fp);
     }
 
@@ -240,9 +239,7 @@ fork_load_infrun_state (struct fork_info
   extern void nullify_last_target_wait_ptid ();
   int i;
 
-  inferior_ptid = fp->ptid;
-
-  linux_nat_switch_fork (inferior_ptid);
+  linux_nat_switch_fork (fp->ptid);
 
   if (fp->savedregs && fp->clobber_regs)
     regcache_cpy (get_current_regcache (), fp->savedregs);
@@ -268,7 +265,7 @@ fork_load_infrun_state (struct fork_info
 /* Save infrun state for the fork PTID.
    Exported for use by linux child_follow_fork.  */
 
-extern void
+static void
 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 {
   char path[MAXPATHLEN];
@@ -280,7 +277,6 @@ fork_save_infrun_state (struct fork_info
 
   fp->savedregs = regcache_dup (get_current_regcache ());
   fp->clobber_regs = clobber_regs;
-  fp->pc = regcache_read_pc (get_current_regcache ());
 
   if (clobber_regs)
     {
@@ -370,8 +366,6 @@ linux_fork_mourn_inferior (void)
      We need to delete that one from the fork_list, and switch
      to the next available fork.  */
   delete_fork (inferior_ptid);
-  /* Delete process from GDB's inferior list.  */
-  delete_inferior (ptid_get_pid (inferior_ptid));
 
   /* There should still be a fork - if there's only one left,
      delete_fork won't remove it, because we haven't updated
@@ -402,8 +396,6 @@ linux_fork_detach (char *args, int from_
     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 
   delete_fork (inferior_ptid);
-  /* Delete process from GDB's inferior list.  */
-  delete_inferior (ptid_get_pid (inferior_ptid));
 
   /* There should still be a fork - if there's only one left,
      delete_fork won't remove it, because we haven't updated
@@ -429,14 +421,14 @@ delete_fork_command (char *args, int fro
   ptid_t ptid;
 
   if (!args || !*args)
-    error (_("Requires argument (fork/checkpoint id to delete)"));
+    error (_("Requires argument (checkpoint id to delete)"));
 
   ptid = fork_id_to_ptid (parse_and_eval_long (args));
   if (ptid_equal (ptid, minus_one_ptid))
-    error (_("No such fork/checkpoint id, %s"), args);
+    error (_("No such checkpoint id, %s"), args);
 
   if (ptid_equal (ptid, inferior_ptid))
-    error (_("Please switch to another fork/checkpoint before deleting the current one"));
+    error (_("Please switch to another checkpoint before deleting the current one"));
 
   if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
@@ -445,8 +437,6 @@ delete_fork_command (char *args, int fro
     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 
   delete_fork (ptid);
-  /* Delete process from GDB's inferior list.  */
-  delete_inferior (ptid_get_pid (ptid));
 }
 
 static void
@@ -455,14 +445,15 @@ detach_fork_command (char *args, int fro
   ptid_t ptid;
 
   if (!args || !*args)
-    error (_("Requires argument (fork id to detach)"));
+    error (_("Requires argument (checkpoint id to detach)"));
 
   ptid = fork_id_to_ptid (parse_and_eval_long (args));
   if (ptid_equal (ptid, minus_one_ptid))
-    error (_("No such fork id, %s"), args);
+    error (_("No such checkpoint id, %s"), args);
 
   if (ptid_equal (ptid, inferior_ptid))
-    error (_("Please switch to another fork before detaching the current one"));
+    error (_("\
+Please switch to another checkpoint before detaching the current one"));
 
   if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
     error (_("Unable to detach %s"), target_pid_to_str (ptid));
@@ -471,8 +462,6 @@ detach_fork_command (char *args, int fro
     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 
   delete_fork (ptid);
-  /* Delete process from GDB's process table.  */
-  detach_inferior (ptid_get_pid (ptid));
 }
 
 /* Print information about currently known forks.  */
@@ -506,7 +495,7 @@ info_forks_command (char *arg, int from_
       else
 	{
 	  printf_filtered ("  ");
-	  pc = fp->pc;
+	  pc = regcache_read_pc (fp->savedregs);
 	}
       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
       if (fp->num == 0)
@@ -546,25 +535,13 @@ info_forks_command (char *arg, int from_
     }
 }
 
-/* Save/restore mode variable 'detach_fork':
-   We need to temporarily take over this mode variable, while
-   preserving the user-specified state, and make sure that it 
-   gets restored in case of error.
+/* The PID of the process we're checkpointing.  */
+static int checkpointing_pid = 0;
 
-   The int pointer that we use comes from the caller, so we can
-   be called more than once (even though currently we don't need to).  */
-
-static void 
-restore_detach_fork (void *arg)
+int
+linux_fork_checkpointing_p (int pid)
 {
-  detach_fork = *(int *) arg;
-}
-
-static struct cleanup *
-save_detach_fork (int *saved_val)
-{
-  *saved_val = detach_fork;
-  return make_cleanup (restore_detach_fork, (void *) saved_val);
+  return (checkpointing_pid == pid);
 }
 
 static void
@@ -579,12 +556,6 @@ checkpoint_command (char *args, int from
   pid_t retpid;
   struct cleanup *old_chain;
   long i;
-  /* Make this temp var static, 'cause it's used in the error context.  */
-  static int temp_detach_fork;
-
-  /* Remove breakpoints, so that they are not inserted
-     in the forked process.  */
-  remove_breakpoints ();
 
   /* Make the inferior fork, record its (and gdb's) state.  */
 
@@ -598,8 +569,11 @@ checkpoint_command (char *args, int from
 
   gdbarch = get_objfile_arch (fork_objf);
   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
-  old_chain = save_detach_fork (&temp_detach_fork);
-  detach_fork = 0;
+
+  /* Tell linux-nat.c that we're checkpointing this inferior.  */
+  old_chain = make_cleanup_restore_integer (&checkpointing_pid);
+  checkpointing_pid = PIDGET (inferior_ptid);
+
   ret = call_function_by_hand (fork_fn, 0, &ret);
   do_cleanups (old_chain);
   if (!ret)	/* Probably can't happen.  */
@@ -627,7 +601,6 @@ checkpoint_command (char *args, int from
   if (!fp)
     error (_("Failed to find new fork"));
   fork_save_infrun_state (fp, 1);
-  insert_breakpoints ();
 }
 
 static void
@@ -654,37 +627,7 @@ linux_fork_context (struct fork_info *ne
   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
 }
 
-/* Switch inferior process (fork) context, by process id.  */
-static void
-process_command (char *args, int from_tty)
-{
-  struct fork_info *fp;
-
-  if (!args || !*args)
-    error (_("Requires argument (process id to switch to)"));
-
-  if ((fp = find_fork_pid (parse_and_eval_long (args))) == NULL)
-    error (_("Not found: process id %s"), args);
-
-  linux_fork_context (fp, from_tty);
-}
-
-/* Switch inferior process (fork) context, by fork id.  */
-static void
-fork_command (char *args, int from_tty)
-{
-  struct fork_info *fp;
-
-  if (!args || !*args)
-    error (_("Requires argument (fork id to switch to)"));
-
-  if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
-    error (_("Not found: fork id %s"), args);
-
-  linux_fork_context (fp, from_tty);
-}
-
-/* Switch inferior process (fork) context, by checkpoint id.  */
+/* Switch inferior process (checkpoint) context, by checkpoint id.  */
 static void
 restart_command (char *args, int from_tty)
 {
@@ -725,9 +668,8 @@ Tells gdb whether to detach the child of
   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 Fork a duplicate process (experimental)."));
 
-  /* Restart command: restore the context of a specified fork
-     process.  May be used for "program forks" as well as for
-     "debugger forks" (checkpoints).  */
+  /* Restart command: restore the context of a specified checkpoint
+     process.  */
 
   add_com ("restart", class_obscure, restart_command, _("\
 restart <n>: restore program context from a checkpoint.\n\
@@ -752,21 +694,4 @@ Detach from a fork/checkpoint (experimen
 
   add_info ("checkpoints", info_forks_command,
 	    _("IDs of currently known forks/checkpoints."));
-
-  /* Command aliases (let "fork" and "checkpoint" be used 
-     interchangeably).  */
-
-  add_alias_cmd ("fork", "checkpoint", class_obscure, 1, &deletelist);
-  add_alias_cmd ("fork", "checkpoint", class_obscure, 1, &detachlist);
-  add_info_alias ("forks", "checkpoints", 0);
-
-  /* "fork <n>" (by analogy to "thread <n>").  */
-  add_com ("fork", class_obscure, fork_command, _("\
-fork <n>: Switch between forked processes.\n\
-Argument 'n' is fork ID, as displayed by 'info forks'."));
-
-  /* "process <proc id>" as opposed to "fork <fork id>".  */
-  add_com ("process", class_obscure, process_command, _("\
-process <pid>: Switch between forked processes.\n\
-Argument 'pid' is process ID, as displayed by 'info forks' or 'shell ps'."));
 }
Index: src/gdb/linux-fork.h
===================================================================
--- src.orig/gdb/linux-fork.h	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/linux-fork.h	2009-05-30 23:03:52.000000000 +0100
@@ -20,13 +20,11 @@
 struct fork_info;
 extern struct fork_info *add_fork (pid_t);
 extern struct fork_info *find_fork_pid (pid_t);
-extern void fork_save_infrun_state (struct fork_info *, int);
 extern void linux_fork_killall (void);
 extern void linux_fork_mourn_inferior (void);
 extern void linux_fork_detach (char *, int);
-extern int  forks_exist_p (void);
-
-struct fork_info *fork_list;
+extern int forks_exist_p (void);
+extern int linux_fork_checkpointing_p (int);
 
 extern int detach_fork;
 
Index: src/gdb/cli/cli-cmds.c
===================================================================
--- src.orig/gdb/cli/cli-cmds.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/cli/cli-cmds.c	2009-05-30 23:03:52.000000000 +0100
@@ -124,6 +124,10 @@ struct cmd_list_element *deletelist;
 
 struct cmd_list_element *detachlist;
 
+/* Chain containing all defined kill subcommands. */
+
+struct cmd_list_element *killlist;
+
 /* Chain containing all defined "enable breakpoint" subcommands. */
 
 struct cmd_list_element *enablebreaklist;
Index: src/gdb/cli/cli-cmds.h
===================================================================
--- src.orig/gdb/cli/cli-cmds.h	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/cli/cli-cmds.h	2009-05-30 23:03:52.000000000 +0100
@@ -41,6 +41,10 @@ extern struct cmd_list_element *deleteli
 
 extern struct cmd_list_element *detachlist;
 
+/* Chain containing all defined kill subcommands.  */
+
+extern struct cmd_list_element *killlist;
+
 /* Chain containing all defined toggle subcommands. */
 
 extern struct cmd_list_element *togglelist;
Index: src/gdb/gdbcmd.h
===================================================================
--- src.orig/gdb/gdbcmd.h	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/gdbcmd.h	2009-05-30 23:03:52.000000000 +0100
@@ -52,6 +52,10 @@ extern struct cmd_list_element *deleteli
 
 extern struct cmd_list_element *detachlist;
 
+/* Chain containing all defined kill subcommands.  */
+
+extern struct cmd_list_element *killlist;
+
 /* Chain containing all defined toggle subcommands.  */
 
 extern struct cmd_list_element *togglelist;
Index: src/gdb/inferior.c
===================================================================
--- src.orig/gdb/inferior.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/inferior.c	2009-05-30 23:03:52.000000000 +0100
@@ -25,6 +25,7 @@
 #include "gdbthread.h"
 #include "ui-out.h"
 #include "observer.h"
+#include "gdbthread.h"
 
 void _initialize_inferiors (void);
 
@@ -322,12 +323,114 @@ print_inferior (struct ui_out *uiout, in
   do_cleanups (old_chain);
 }
 
+static void
+detach_inferior_command (char *args, int from_tty)
+{
+  int num = -1;
+  int pid;
+  struct thread_info *tp;
+
+  if (!args || !*args)
+    error (_("Requires argument (inferior id to detach)"));
+
+  num = parse_and_eval_long (args);
+
+  if (!valid_gdb_inferior_id (num))
+    error (_("Inferior ID %d not known."), num);
+
+  pid = gdb_inferior_id_to_pid (num);
+
+  tp = any_thread_of_process (pid);
+  if (!tp)
+    error (_("Inferior has no threads."));
+
+  switch_to_thread (tp->ptid);
+
+  detach_command (NULL, from_tty);
+}
+
+static void
+kill_inferior_command (char *args, int from_tty)
+{
+  int num = -1;
+  int pid;
+  struct thread_info *tp;
+
+  if (!args || !*args)
+    error (_("Requires argument (inferior id to kill)"));
+
+  num = parse_and_eval_long (args);
+
+  if (!valid_gdb_inferior_id (num))
+    error (_("Inferior ID %d not known."), num);
+
+  pid = gdb_inferior_id_to_pid (num);
+
+  tp = any_thread_of_process (pid);
+  if (!tp)
+    error (_("Inferior has no threads."));
+
+  switch_to_thread (tp->ptid);
+
+  target_kill ();
+
+  bfd_cache_close_all ();
+}
+
+static void
+inferior_command (char *args, int from_tty)
+{
+  int num, pid;
+
+  if (!have_inferiors ())
+    error (_("No inferiors"));
+
+  num = parse_and_eval_long (args);
+
+  if (!valid_gdb_inferior_id (num))
+    error (_("Inferior ID %d not known."), num);
+
+  pid = gdb_inferior_id_to_pid (num);
+
+  if (pid != ptid_get_pid (inferior_ptid))
+    {
+      struct thread_info *tp;
+
+      tp = any_thread_of_process (pid);
+      if (!tp)
+	error (_("Inferior has no threads."));
+
+      switch_to_thread (tp->ptid);
+    }
+
+  printf_filtered (_("[Switching to thread %d (%s)] "),
+		   pid_to_thread_id (inferior_ptid),
+		   target_pid_to_str (inferior_ptid));
+
+  if (is_running (inferior_ptid))
+    ui_out_text (uiout, "(running)\n");
+  else
+    {
+      ui_out_text (uiout, "\n");
+      print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
+    }
+}
+
 /* Print information about currently known inferiors.  */
 
 static void
-info_inferiors_command (char *arg, int from_tty)
+info_inferiors_command (char *args, int from_tty)
 {
-  print_inferior (uiout, -1);
+  int requested = -1;
+
+  if (args && *args)
+    {
+      requested = parse_and_eval_long (args);
+      if (!valid_gdb_inferior_id (requested))
+	error (_("Inferior ID %d not known."), requested);
+    }
+
+  print_inferior (uiout, requested);
 }
 
 /* Print notices when new inferiors are created and die.  */
@@ -351,4 +454,17 @@ Show printing of inferior events (e.g., 
          NULL,
          show_print_inferior_events,
          &setprintlist, &showprintlist);
+
+  add_cmd ("inferior", class_run, detach_inferior_command, _("\
+Detach from inferior ID."),
+	   &detachlist);
+
+  add_cmd ("inferior", class_run, kill_inferior_command, _("\
+Kill inferior ID."),
+	   &killlist);
+
+  add_cmd ("inferior", class_run, inferior_command, _("\
+Use this command to switch between inferiors.\n\
+The new inferior ID must be currently known."),
+	   &cmdlist);
 }
Index: src/gdb/testsuite/gdb.base/multi-forks.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.base/multi-forks.exp	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/testsuite/gdb.base/multi-forks.exp	2009-05-30 23:03:52.000000000 +0100
@@ -140,6 +140,19 @@ gdb_test "print pids\[0\]==0 || pids\[1\
 # Now test with detach-on-fork off.
 #
 
+# detach-on-fork isn't implemented on hpux.
+#
+if {![istarget "*-*-linux*"]} then {
+    continue
+}
+
+# Start with a fresh gdb
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
 runto_main
 gdb_breakpoint $exit_bp_loc
 
@@ -152,60 +165,59 @@ gdb_test "set detach off" "" "set detach
 
 #
 # We will now run every fork up to the exit bp, 
-# eventually winding up with 16 forks.
+# eventually winding up with 16 inferiors.
 #
 
 for {set i 1} {$i <= 15} {incr i} {
   gdb_test "continue" "Breakpoint .* main .*exit.*" "Run to exit $i"
-  gdb_test "info fork" " 4 .* 3 .* 2 .* 1 .*" "info fork $i"
-  gdb_test "restart $i" "(_dl_sysinfo_int80|fork|__kernel_(v|)syscall).*" \
-      "restart $i"
+  gdb_test "info inferior" " 5 .* 4 .* 3 .* 2 .*" "info inferior $i"
+  gdb_test "inferior $i + 1" "(_dl_sysinfo_int80|fork|__kernel_(v|)syscall).*" \
+      "inferior $i"
 }
 
 gdb_test "continue" "Breakpoint .* main .*exit.*" "Run to exit 16"
-gdb_test "info fork" " 4 .* 3 .* 2 .* 1 .*" "info fork 16"
-gdb_test "restart 0" " main .*" "restart final"
+gdb_test "info inferiors" " 5 .* 4 .* 3 .* 2 .*" "info inferior 16"
+gdb_test "inferior 2" " main .*" "restart final"
 
 #
 # Now we should examine all the pids.
 #
 
 # 
-# Test detach fork
+# Test detach inferior
 # 
 
-# [assumes we're at #0]
-gdb_test "detach fork 1" "Detached .*" "Detach 1"
-gdb_test "detach fork 2" "Detached .*" "Detach 2"
-gdb_test "detach fork 3" "Detached .*" "Detach 3"
-gdb_test "detach fork 4" "Detached .*" "Detach 4"
+# [assumes we're at #1]
+gdb_test "detach inferior 2" "Detaching .*" "Detach 2"
+gdb_test "detach inferior 3" "Detaching .*" "Detach 3"
+gdb_test "detach inferior 4" "Detaching .*" "Detach 4"
+gdb_test "detach inferior 5" "Detaching .*" "Detach 5"
 
 # 
-# Test delete fork
-# 
+# Test kill inferior
+#
 
-gdb_test "delete fork 5" "" "Delete 5"
-gdb_test "info fork 5"   "No fork number 5." "Did delete 5"
-gdb_test "delete fork 6" "" "Delete 6"
-gdb_test "info fork 6"   "No fork number 6." "Did delete 6"
-gdb_test "delete fork 7" "" "Delete 7"
-gdb_test "info fork 7"   "No fork number 7." "Did delete 7"
-gdb_test "delete fork 8" "" "Delete 8"
-gdb_test "info fork 8"   "No fork number 8." "Did delete 8"
-gdb_test "delete fork 9" "" "Delete 9"
-gdb_test "info fork 9"   "No fork number 9." "Did delete 9"
-gdb_test "delete fork 10" "" "Delete 10"
-gdb_test "info fork 10"   "No fork number 10." "Did delete 10"
-gdb_test "delete fork 11" "" "Delete 11"
-gdb_test "info fork 11"   "No fork number 11." "Did delete 11"
-gdb_test "delete fork 12" "" "Delete 12"
-gdb_test "info fork 12"   "No fork number 12." "Did delete 12"
-gdb_test "delete fork 13" "" "Delete 13"
-gdb_test "info fork 13"   "No fork number 13." "Did delete 13"
-gdb_test "delete fork 14" "" "Delete 14"
-gdb_test "info fork 14"   "No fork number 14." "Did delete 14"
-gdb_test "delete fork 15" "" "Delete 15"
-gdb_test "info fork 15"   "No fork number 15." "Did delete 15"
+gdb_test "kill inferior 6" "" "Kill 6"
+gdb_test "info inferior 6" "Inferior ID 6 not known." "Did kill 6"
+gdb_test "kill inferior 7" "" "Kill 7"
+gdb_test "info inferior 7" "Inferior ID 7 not known." "Did kill 7"
+gdb_test "kill inferior 8" "" "Kill 8"
+gdb_test "info inferior 8" "Inferior ID 8 not known." "Did kill 8"
+gdb_test "kill inferior 9" "" "Kill 9"
+gdb_test "info inferior 9" "Inferior ID 9 not known." "Did kill 9"
+gdb_test "kill inferior 10" "" "Kill 10"
+gdb_test "info inferior 10" "Inferior ID 10 not known." "Did kill 10"
+gdb_test "kill inferior 11" "" "Kill 11"
+gdb_test "info inferior 11" "Inferior ID 11 not known." "Did kill 11"
+gdb_test "kill inferior 12" "" "Kill 12"
+gdb_test "info inferior 12" "Inferior ID 12 not known." "Did kill 12"
+gdb_test "kill inferior 13" "" "Kill 13"
+gdb_test "info inferior 13" "Inferior ID 13 not known." "Did kill 13"
+gdb_test "kill inferior 14" "" "Kill 14"
+gdb_test "info inferior 14" "Inferior ID 14 not known." "Did kill 14"
+gdb_test "kill inferior 15" "" "Kill 15"
+gdb_test "info inferior 15" "Inferior ID 15 not known." "Did kill 15"
+gdb_test "kill inferior 16" "" "Kill 16"
+gdb_test "info inferior 16" "Inferior ID 16 not known." "Did kill 16"
 
 return 0
-
Index: src/gdb/testsuite/gdb.base/ending-run.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.base/ending-run.exp	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/testsuite/gdb.base/ending-run.exp	2009-05-30 23:03:52.000000000 +0100
@@ -71,7 +71,7 @@ gdb_test "b ending-run.c:14" ".*Note.*al
 gdb_test "cle ending-run.c:14" \
 	".*Deleted breakpoint 5.*" "Cleared 2 by line"
 
-send_gdb "inf line ending-run.c:14\n"
+send_gdb "info line ending-run.c:14\n"
 gdb_expect {
     -re ".*address (0x\[0-9a-fA-F]*).*$gdb_prompt $" {
         set line_nine $expect_out(1,string)
Index: src/gdb/testsuite/gdb.base/help.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.base/help.exp	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/testsuite/gdb.base/help.exp	2009-05-30 23:03:52.000000000 +0100
@@ -300,7 +300,9 @@ gdb_test "help inspect" "Same as \"print
 # test help jump
 gdb_test "help jump" "Continue program being debugged at specified line or address\.\[\r\n\]+Give as argument either LINENUM or \[*\]+ADDR, where ADDR is an expression\[\r\n\]+for an address to start at\." "help jump"
 # test help kill
-gdb_test "help kill" "Kill execution of program being debugged\." "help kill"
+test_prefix_command_help "kill" {
+    "Kill execution of program being debugged\.\[\r\n\]+"
+}
 # test help list "l" abbreviation
 gdb_test "help l" "List specified function or line\.\[\r\n\]+With no argument, lists ten more lines after or around previous listing\.\[\r\n\]+\"list -\" lists the ten lines before a previous ten-line listing\.\[\r\n\]+One argument specifies a line, and ten lines are listed around that line\.\[\r\n\]+Two arguments with comma between specify starting and ending lines to list\.\[\r\n\]+Lines can be specified in these ways:\[\r\n\]+  LINENUM, to list around that line in current file,\[\r\n\]+  FILE:LINENUM, to list around that line in that file,\[\r\n\]+  FUNCTION, to list around beginning of that function,\[\r\n\]+  FILE:FUNCTION, to distinguish among like-named static functions\.\[\r\n\]+  \[*\]ADDRESS, to list around the line containing that address\.\[\r\n\]+With two args if one is empty it stands for ten lines away from the other arg\." "help list \"l\" abbreviation"
 # test help list
Index: src/gdb/infcmd.c
===================================================================
--- src.orig/gdb/infcmd.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/infcmd.c	2009-05-30 23:03:52.000000000 +0100
@@ -2626,8 +2626,9 @@ fully linked executable files and separa
 	       &showlist);
   set_cmd_completer (c, noop_completer);
 
-  add_com ("kill", class_run, kill_command,
-	   _("Kill execution of program being debugged."));
+  add_prefix_cmd ("kill", class_run, kill_command,
+		  _("Kill execution of program being debugged."),
+		  &killlist, "kill ", 0, &cmdlist);
 
   add_com ("attach", class_run, attach_command, _("\
 Attach to a process or file outside of GDB.\n\
Index: src/gdb/gdbthread.h
===================================================================
--- src.orig/gdb/gdbthread.h	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/gdbthread.h	2009-05-30 23:03:52.000000000 +0100
@@ -238,6 +238,9 @@ struct thread_info *find_thread_id (int 
    returns the first thread in the list.  */
 struct thread_info *first_thread_of_process (int pid);
 
+/* Returns any thread of process PID.  */
+extern struct thread_info *any_thread_of_process (int pid);
+
 /* Change the ptid of thread OLD_PTID to NEW_PTID.  */
 void thread_change_ptid (ptid_t old_ptid, ptid_t new_ptid);
 
Index: src/gdb/thread.c
===================================================================
--- src.orig/gdb/thread.c	2009-05-30 23:03:28.000000000 +0100
+++ src/gdb/thread.c	2009-05-30 23:03:52.000000000 +0100
@@ -428,6 +428,18 @@ first_thread_of_process (int pid)
   return ret;
 }
 
+struct thread_info *
+any_thread_of_process (int pid)
+{
+  struct thread_info *tp;
+
+  for (tp = thread_list; tp; tp = tp->next)
+    if (ptid_get_pid (tp->ptid) == pid)
+      return tp;
+
+  return NULL;
+}
+
 /* Print a list of thread ids currently known, and the total number of
    threads. To be used from within catch_errors. */
 static int
Index: src/gdb/doc/gdb.texinfo
===================================================================
--- src.orig/gdb/doc/gdb.texinfo	2009-05-30 23:03:25.000000000 +0100
+++ src/gdb/doc/gdb.texinfo	2009-05-30 23:03:52.000000000 +0100
@@ -2388,7 +2388,39 @@ To find out what inferiors exist at any 
 @kindex info inferiors
 @item info inferiors
 Print a list of all inferiors currently being managed by @value{GDBN}.
+@end table
+
+To switch focus between inferiors, use the @code{inferior} command:
+
+@table @code
+@kindex inferior @var{inferior-id}
+@item inferior @var{inferior-id}
+Make inferior number @var{inferior-id} the current inferior.  The
+argument @var{inferior-id} is the internal inferior number assigned by
+@value{GDBN}, as shown in the first field of the @samp{info inferiors}
+display.
+@end table
+
+To quit debugging one of the inferiors, you can either detach from it
+by using the @w{@code{detach inferior}} command (allowing it to run
+independently), or kill it using the @w{@code{kill inferior}} command:
+
+@table @code
+@kindex detach inferior @var{inferior-id}
+@item detach inferior @var{inferior-id}
+Detach from the inferior identified by @value{GDBN} inferior number
+@var{inferior-id}, and remove it from the inferior list.
+
+@kindex kill inferior @var{inferior-id}
+@item kill inferior @var{inferior-id}
+Kill the inferior identified by @value{GDBN} inferior number
+@var{inferior-id}, and remove it from the inferior list.
+@end table
+
+To be notified when inferiors are started or exit under @value{GDBN}'s
+control use @w{@code{set print inferior-events}}:
 
+@table @code
 @kindex set print inferior-events
 @cindex print messages on inferior start and exit
 @item set print inferior-events
@@ -2772,51 +2804,17 @@ is held suspended.  
 Show whether detach-on-fork mode is on/off.
 @end table
 
-If you choose to set @samp{detach-on-fork} mode off, then
-@value{GDBN} will retain control of all forked processes (including
-nested forks).  You can list the forked processes under the control of
-@value{GDBN} by using the @w{@code{info forks}} command, and switch
-from one fork to another by using the @w{@code{fork}} command.
-
-@table @code
-@kindex info forks
-@item info forks
-Print a list of all forked processes under the control of @value{GDBN}.
-The listing will include a fork id, a process id, and the current 
-position (program counter) of the process.
-
-@kindex fork @var{fork-id}
-@item fork @var{fork-id}
-Make fork number @var{fork-id} the current process.  The argument
-@var{fork-id} is the internal fork number assigned by @value{GDBN},
-as shown in the first field of the @samp{info forks} display.
-
-@kindex process @var{process-id}
-@item process @var{process-id}
-Make process number @var{process-id} the current process.  The
-argument @var{process-id} must be one that is listed in the output of
-@samp{info forks}.
-
-@end table
+If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
+will retain control of all forked processes (including nested forks).
+You can list the forked processes under the control of @value{GDBN} by
+using the @w{@code{info inferiors}} command, and switch from one fork
+to another by using the @w{@code{inferior}} command (@pxref{Inferiors,
+,Debugging Multiple Inferiors}).
 
 To quit debugging one of the forked processes, you can either detach
-from it by using the @w{@code{detach fork}} command (allowing it to
-run independently), or delete (and kill) it using the
-@w{@code{delete fork}} command.
-
-@table @code
-@kindex detach fork @var{fork-id}
-@item detach fork @var{fork-id}
-Detach from the process identified by @value{GDBN} fork number
-@var{fork-id}, and remove it from the fork list.  The process will be
-allowed to run independently.
-
-@kindex delete fork @var{fork-id}
-@item delete fork @var{fork-id}
-Kill the process identified by @value{GDBN} fork number @var{fork-id},
-and remove it from the fork list.
-
-@end table
+from it by using the @w{@code{detach inferior}} command (allowing it
+to run independently), or kill it using the @w{@code{kill inferior}}
+command.  Again, @pxref{Inferiors, ,Debugging Multiple Inferiors},
 
 If you ask to debug a child process and a @code{vfork} is followed by an
 @code{exec}, @value{GDBN} executes the new target up to the first
@@ -2824,8 +2822,8 @@ breakpoint in the new target.  If you ha
 @code{main} in your original program, the breakpoint will also be set on
 the child process's @code{main}.
 
-When a child process is spawned by @code{vfork}, you cannot debug the
-child or parent until an @code{exec} call completes.
+On some systems, when a child process is spawned by @code{vfork}, you
+cannot debug the child or parent until an @code{exec} call completes.
 
 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
 call executes, the new target restarts.  To restart the parent process,


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