From: Pedro Alves <palves@redhat.com>
Date: Wed, 13 Feb 2013 14:59:49 +0000 (+0000)
Subject: [native x86 GNU/Linux] Access debug register mirror from the corresponding process.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=26cb8b7c1a23586ea311d7480f882e2883f6f1f5;p=binutils-gdb.git

[native x86 GNU/Linux] Access debug register mirror from the corresponding process.

While reviewing the native AArch64 patch, I noticed a problem:

On 02/06/2013 08:46 PM, Pedro Alves wrote:
>
>> > +static void
>> > +aarch64_linux_prepare_to_resume (struct lwp_info *lwp)
>> > +{
>> > +  struct arch_lwp_info *info = lwp->arch_private;
>> > +
>> > +  /* NULL means this is the main thread still going through the shell,
>> > +     or, no watchpoint has been set yet.  In that case, there's
>> > +     nothing to do.  */
>> > +  if (info == NULL)
>> > +    return;
>> > +
>> > +  if (DR_HAS_CHANGED (info->dr_changed_bp)
>> > +      || DR_HAS_CHANGED (info->dr_changed_wp))
>> > +    {
>> > +      int tid = GET_LWP (lwp->ptid);
>> > +      struct aarch64_debug_reg_state *state = aarch64_get_debug_reg_state ();
> Hmm.  This is always fetching the debug_reg_state of
> the current inferior, but may not be the inferior of lwp.
> I see the same bug on x86.  Sorry about that.  I'll fix it.

A natural fix would be to make xxx_get_debug_reg_state take an
inferior argument, but that doesn't work because of the case where we
detach breakpoints/watchpoints from the child fork, at a time there's
no inferior for the child fork at all.  We do a nasty hack in
i386_inferior_data_get, but that relies on all callers pointing the
current inferior to the correct inferior, which isn't actually being
done by all callers, and I don't think we want to enforce that -- deep
in the bowls of linux-nat.c, there are many cases we resume lwps
behind the scenes, and it's be better to not have that code rely on
global state (as it doesn't today).

The fix is to decouple the watchpoints code from inferiors, making it
track target processes instead.  This way, we can freely keep track of
the watchpoint mirrors for these processes behind the core's back.
Checkpoints also play dirty tricks with swapping the process behind
the inferior, so they get special treatment too in the patch (which
just amounts to calling a new hook).  Instead of the old hack in
i386_inferior_data_get, where we returned a copy of the current
inferior's debug registers mirror, as soon as we detect a fork in the
target, we copy the debug register mirror from the parent to the child
process.

I don't have an old kernel handy to test, but I stepped through gdb doing
the watchpoint removal in the fork child in the watchpoint-fork test
seeing that the debug registers end up cleared in the child.

I didn't find the need for linux_nat_iterate_watchpoint_lwps.  If
we use plain iterate_over_lwps instead, what happens is that
when removing watchpoints, that iterate_over_lwps doesn't actually
iterate over anything, since the fork child is not added to the
lwp list until later, at detach time, in linux_child_follow_fork.
And if we don't iterate over that lwp, we don't mark its debug
registers as needing update.  But linux_child_follow_fork takes
care of doing that explicitly:

	  child_lp = add_lwp (inferior_ptid);
	  child_lp->stopped = 1;
	  child_lp->last_resume_kind = resume_stop;
	  make_cleanup (delete_lwp_cleanup, child_lp);

	  /* CHILD_LP has new PID, therefore linux_nat_new_thread is not called for it.
	     See i386_inferior_data_get for the Linux kernel specifics.
	     Ensure linux_nat_prepare_to_resume will reset the hardware debug
	     registers.  It is done by the linux_nat_new_thread call, which is
	     being skipped in add_lwp above for the first lwp of a pid.  */
	  gdb_assert (num_lwps (GET_PID (child_lp->ptid)) == 1);
	  if (linux_nat_new_thread != NULL)
	    linux_nat_new_thread (child_lp);

	  if (linux_nat_prepare_to_resume != NULL)
	    linux_nat_prepare_to_resume (child_lp);
	  ptrace (PTRACE_DETACH, child_pid, 0, 0);

so unless I'm missing something (quite possible) it ends up all
the same.  But, the !detach-on-fork, and the "follow-fork child" paths
should also call linux_nat_new_thread, and they don't presently.  It
seems to me in those cases we're not clearing debug regs correctly
when that's needed.  Instead of copying that bit that works around
add_lwp bypassing the linux_nat_new_thread call, I thought it'd
be better to add an add_initial_lwp call to be used in the case we
really need to bypass linux_nat_new_thread, and make
add_lwp always call linux_nat_new_thread.

i386_cleanup_dregs is rewritten to forget about the current process
debug mirrors, which takes cares of other i386 ports.  Only a couple
of extra tweaks here and there were needed, as some targets wheren't
actually calling i386_cleanup_dregs.

Tested on Fedora 17 x86_64 -m64/-m32.

GDBserver already fetches the i386_debug_reg_state from the right
process, and, it doesn't handle forks at all, so no fix is needed over
there.

gdb/
2013-02-13  Pedro Alves  <palves@redhat.com>

	* amd64-linux-nat.c (update_debug_registers_callback):
	Update comment.
	(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
	iterate_over_lwps.
	(amd64_linux_prepare_to_resume): Pass the lwp's pid to
	i386_debug_reg_state.
	(amd64_linux_new_fork): New function.
	(_initialize_amd64_linux_nat): Install amd64_linux_new_fork as
	linux_nat_new_fork hook, and i386_forget_process as
	linux_nat_forget_process hook.
	* i386-linux-nat.c (update_debug_registers_callback):
	Update comment.
	(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
	iterate_over_lwps.
	(i386_linux_prepare_to_resume): Pass the lwp's pid to
	i386_debug_reg_state.
	(i386_linux_new_fork): New function.
	(_initialize_i386_linux_nat): Install i386_linux_new_fork as
	linux_nat_new_fork hook, and i386_forget_process as
	linux_nat_forget_process hook.
	* i386-nat.c (i386_init_dregs): Delete.
	(i386_inferior_data, struct i386_inferior_data):
	Delete.
	(struct i386_process_info): New.
	(i386_process_list): New global.
	(i386_find_process_pid, i386_add_process, i386_process_info_get):
	New functions.
	(i386_inferior_data_get): Delete.
	(i386_process_info_get): New function.
	(i386_debug_reg_state): New parameter 'pid'.  Reimplement.
	(i386_forget_process): New function.
	(i386_cleanup_dregs): Rewrite.
	(i386_update_inferior_debug_regs, i386_insert_watchpoint)
	(i386_remove_watchpoint, i386_region_ok_for_watchpoint)
	(i386_stopped_data_address, i386_insert_hw_breakpoint)
	(i386_remove_hw_breakpoint): Adjust to pass the current process id
	to i386_debug_reg_state.
	(i386_use_watchpoints): Don't register inferior data.
	* i386-nat.h (i386_debug_reg_state): Add new 'pid' parameter, and
	adjust comment.
	(i386_forget_process): Declare.
	* linux-fork.c (delete_fork): Call linux_nat_forget_process.
	* linux-nat.c (linux_nat_new_fork, linux_nat_forget_process_hook):
	New static globals.
	(linux_child_follow_fork): Don't call linux_nat_new_thread here.
	(add_initial_lwp): New, factored out from ...
	(add_lwp): ... this.  Don't check the number of lwps before
	calling linux_nat_new_thread.
	(linux_nat_iterate_watchpoint_lwps): Delete.
	(linux_nat_attach): Use add_initial_lwp instead of add_lwp.
	(linux_handle_extended_wait): Call the linux_nat_new_fork hook on
	forks and vforks.
	(linux_nat_wait_1): Use add_initial_lwp instead of add_lwp for the
	initial lwp.
	(linux_nat_kill, linux_nat_mourn_inferior): Call
	linux_nat_forget_process.
	(linux_nat_set_new_fork, linux_nat_set_forget_process)
	(linux_nat_forget_process): New functions.
	* linux-nat.h (linux_nat_iterate_watchpoint_lwps_ftype): Delete
	type.
	(linux_nat_iterate_watchpoint_lwps): Delete declaration.
	(linux_nat_new_fork_ftype, linux_nat_forget_process_ftype): New
	types.
	(linux_nat_set_new_fork, linux_nat_set_forget_process)
	(linux_nat_forget_process): New declarations.

	* amd64fbsd-nat.c (super_mourn_inferior): New global.
	(amd64fbsd_mourn_inferior): New function.
	(_initialize_amd64fbsd_nat): Override to_mourn_inferior.
	* windows-nat.c (windows_detach): Call i386_cleanup_dregs.
---

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b293389bbbb..24e38e94f15 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,76 @@
+2013-02-13  Pedro Alves  <palves@redhat.com>
+
+	* amd64-linux-nat.c (update_debug_registers_callback):
+	Update comment.
+	(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
+	iterate_over_lwps.
+	(amd64_linux_prepare_to_resume): Pass the lwp's pid to
+	i386_debug_reg_state.
+	(amd64_linux_new_fork): New function.
+	(_initialize_amd64_linux_nat): Install amd64_linux_new_fork as
+	linux_nat_new_fork hook, and i386_forget_process as
+	linux_nat_forget_process hook.
+	* i386-linux-nat.c (update_debug_registers_callback):
+	Update comment.
+	(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
+	iterate_over_lwps.
+	(i386_linux_prepare_to_resume): Pass the lwp's pid to
+	i386_debug_reg_state.
+	(i386_linux_new_fork): New function.
+	(_initialize_i386_linux_nat): Install i386_linux_new_fork as
+	linux_nat_new_fork hook, and i386_forget_process as
+	linux_nat_forget_process hook.
+	* i386-nat.c (i386_init_dregs): Delete.
+	(i386_inferior_data, struct i386_inferior_data):
+	Delete.
+	(struct i386_process_info): New.
+	(i386_process_list): New global.
+	(i386_find_process_pid, i386_add_process, i386_process_info_get):
+	New functions.
+	(i386_inferior_data_get): Delete.
+	(i386_process_info_get): New function.
+	(i386_debug_reg_state): New parameter 'pid'.  Reimplement.
+	(i386_forget_process): New function.
+	(i386_cleanup_dregs): Rewrite.
+	(i386_update_inferior_debug_regs, i386_insert_watchpoint)
+	(i386_remove_watchpoint, i386_region_ok_for_watchpoint)
+	(i386_stopped_data_address, i386_insert_hw_breakpoint)
+	(i386_remove_hw_breakpoint): Adjust to pass the current process id
+	to i386_debug_reg_state.
+	(i386_use_watchpoints): Don't register inferior data.
+	* i386-nat.h (i386_debug_reg_state): Add new 'pid' parameter, and
+	adjust comment.
+	(i386_forget_process): Declare.
+	* linux-fork.c (delete_fork): Call linux_nat_forget_process.
+	* linux-nat.c (linux_nat_new_fork, linux_nat_forget_process_hook):
+	New static globals.
+	(linux_child_follow_fork): Don't call linux_nat_new_thread here.
+	(add_initial_lwp): New, factored out from ...
+	(add_lwp): ... this.  Don't check the number of lwps before
+	calling linux_nat_new_thread.
+	(linux_nat_iterate_watchpoint_lwps): Delete.
+	(linux_nat_attach): Use add_initial_lwp instead of add_lwp.
+	(linux_handle_extended_wait): Call the linux_nat_new_fork hook on
+	forks and vforks.
+	(linux_nat_wait_1): Use add_initial_lwp instead of add_lwp for the
+	initial lwp.
+	(linux_nat_kill, linux_nat_mourn_inferior): Call
+	linux_nat_forget_process.
+	(linux_nat_set_new_fork, linux_nat_set_forget_process)
+	(linux_nat_forget_process): New functions.
+	* linux-nat.h (linux_nat_iterate_watchpoint_lwps_ftype): Delete
+	type.
+	(linux_nat_iterate_watchpoint_lwps): Delete declaration.
+	(linux_nat_new_fork_ftype, linux_nat_forget_process_ftype): New
+	types.
+	(linux_nat_set_new_fork, linux_nat_set_forget_process)
+	(linux_nat_forget_process): New declarations.
+
+	* amd64fbsd-nat.c (super_mourn_inferior): New global.
+	(amd64fbsd_mourn_inferior): New function.
+	(_initialize_amd64fbsd_nat): Override to_mourn_inferior.
+	* windows-nat.c (windows_detach): Call i386_cleanup_dregs.
+
 2013-02-13  Marcus Shawcroft  <marcus.shawcroft@arm.com>
 
 	       * aarch64-linux-nat.c (aarch64_linux_get_debug_reg_capacity)
diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c
index e3e7f05acd9..3d1983b6d15 100644
--- a/gdb/amd64-linux-nat.c
+++ b/gdb/amd64-linux-nat.c
@@ -337,8 +337,8 @@ amd64_linux_dr_get_status (void)
   return amd64_linux_dr_get (inferior_ptid, DR_STATUS);
 }
 
-/* Callback for linux_nat_iterate_watchpoint_lwps.  Update the debug registers
-   of LWP.  */
+/* Callback for iterate_over_lwps.  Update the debug registers of
+   LWP.  */
 
 static int
 update_debug_registers_callback (struct lwp_info *lwp, void *arg)
@@ -364,7 +364,9 @@ update_debug_registers_callback (struct lwp_info *lwp, void *arg)
 static void
 amd64_linux_dr_set_control (unsigned long control)
 {
-  linux_nat_iterate_watchpoint_lwps (update_debug_registers_callback, NULL);
+  ptid_t pid_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
+
+  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
 }
 
 /* Set address REGNUM (zero based) to ADDR in all LWPs of the current
@@ -373,9 +375,11 @@ amd64_linux_dr_set_control (unsigned long control)
 static void
 amd64_linux_dr_set_addr (int regnum, CORE_ADDR addr)
 {
+  ptid_t pid_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
+
   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 
-  linux_nat_iterate_watchpoint_lwps (update_debug_registers_callback, NULL);
+  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
 }
 
 /* Called when resuming a thread.
@@ -394,7 +398,8 @@ amd64_linux_prepare_to_resume (struct lwp_info *lwp)
 
   if (lwp->arch_private->debug_registers_changed)
     {
-      struct i386_debug_reg_state *state = i386_debug_reg_state ();
+      struct i386_debug_reg_state *state
+	= i386_debug_reg_state (ptid_get_pid (lwp->ptid));
       int i;
 
       /* On Linux kernel before 2.6.33 commit
@@ -434,6 +439,41 @@ amd64_linux_new_thread (struct lwp_info *lp)
 
   lp->arch_private = info;
 }
+
+/* linux_nat_new_fork hook.   */
+
+static void
+amd64_linux_new_fork (struct lwp_info *parent, pid_t child_pid)
+{
+  pid_t parent_pid;
+  struct i386_debug_reg_state *parent_state;
+  struct i386_debug_reg_state *child_state;
+
+  /* NULL means no watchpoint has ever been set in the parent.  In
+     that case, there's nothing to do.  */
+  if (parent->arch_private == NULL)
+    return;
+
+  /* Linux kernel before 2.6.33 commit
+     72f674d203cd230426437cdcf7dd6f681dad8b0d
+     will inherit hardware debug registers from parent
+     on fork/vfork/clone.  Newer Linux kernels create such tasks with
+     zeroed debug registers.
+
+     GDB core assumes the child inherits the watchpoints/hw
+     breakpoints of the parent, and will remove them all from the
+     forked off process.  Copy the debug registers mirrors into the
+     new process so that all breakpoints and watchpoints can be
+     removed together.  The debug registers mirror will become zeroed
+     in the end before detaching the forked off process, thus making
+     this compatible with older Linux kernels too.  */
+
+  parent_pid = ptid_get_pid (parent->ptid);
+  parent_state = i386_debug_reg_state (parent_pid);
+  child_state = i386_debug_reg_state (child_pid);
+  *child_state = *parent_state;
+}
+
 
 
 /* This function is called by libthread_db as part of its handling of
@@ -1120,6 +1160,8 @@ _initialize_amd64_linux_nat (void)
   /* Register the target.  */
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, amd64_linux_new_thread);
+  linux_nat_set_new_fork (t, amd64_linux_new_fork);
+  linux_nat_set_forget_process (t, i386_forget_process);
   linux_nat_set_siginfo_fixup (t, amd64_linux_siginfo_fixup);
   linux_nat_set_prepare_to_resume (t, amd64_linux_prepare_to_resume);
 }
diff --git a/gdb/amd64fbsd-nat.c b/gdb/amd64fbsd-nat.c
index a500a6676b3..eb30831539c 100644
--- a/gdb/amd64fbsd-nat.c
+++ b/gdb/amd64fbsd-nat.c
@@ -142,6 +142,17 @@ amd64fbsd_supply_pcb (struct regcache *regcache, struct pcb *pcb)
 }
 
 
+static void (*super_mourn_inferior) (struct target_ops *ops);
+
+static void
+amd64fbsd_mourn_inferior (struct target_ops *ops)
+{
+#ifdef HAVE_PT_GETDBREGS
+  i386_cleanup_dregs ();
+#endif
+  super_mourn_inferior (ops);
+}
+
 /* Provide a prototype to silence -Wmissing-prototypes.  */
 void _initialize_amd64fbsd_nat (void);
 
@@ -170,6 +181,9 @@ _initialize_amd64fbsd_nat (void)
 
 #endif /* HAVE_PT_GETDBREGS */
 
+  super_mourn_inferior = t->to_mourn_inferior;
+  t->to_mourn_inferior = amd64fbsd_mourn_inferior;
+
   t->to_pid_to_exec_file = fbsd_pid_to_exec_file;
   t->to_find_memory_regions = fbsd_find_memory_regions;
   t->to_make_corefile_notes = fbsd_make_corefile_notes;
diff --git a/gdb/i386-linux-nat.c b/gdb/i386-linux-nat.c
index 20cc0327800..11b510dc493 100644
--- a/gdb/i386-linux-nat.c
+++ b/gdb/i386-linux-nat.c
@@ -708,8 +708,8 @@ i386_linux_dr_get_status (void)
   return i386_linux_dr_get (inferior_ptid, DR_STATUS);
 }
 
-/* Callback for linux_nat_iterate_watchpoint_lwps.  Update the debug registers
-   of LWP.  */
+/* Callback for iterate_over_lwps.  Update the debug registers of
+   LWP.  */
 
 static int
 update_debug_registers_callback (struct lwp_info *lwp, void *arg)
@@ -735,7 +735,9 @@ update_debug_registers_callback (struct lwp_info *lwp, void *arg)
 static void
 i386_linux_dr_set_control (unsigned long control)
 {
-  linux_nat_iterate_watchpoint_lwps (update_debug_registers_callback, NULL);
+  ptid_t pid_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
+
+  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
 }
 
 /* Set address REGNUM (zero based) to ADDR in all LWPs of the current
@@ -748,7 +750,7 @@ i386_linux_dr_set_addr (int regnum, CORE_ADDR addr)
 
   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 
-  linux_nat_iterate_watchpoint_lwps (update_debug_registers_callback, NULL);
+  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
 }
 
 /* Called when resuming a thread.
@@ -767,7 +769,8 @@ i386_linux_prepare_to_resume (struct lwp_info *lwp)
 
   if (lwp->arch_private->debug_registers_changed)
     {
-      struct i386_debug_reg_state *state = i386_debug_reg_state ();
+      struct i386_debug_reg_state *state
+	= i386_debug_reg_state (ptid_get_pid (lwp->ptid));
       int i;
 
       /* See amd64_linux_prepare_to_resume for Linux kernel note on
@@ -803,6 +806,41 @@ i386_linux_new_thread (struct lwp_info *lp)
 
   lp->arch_private = info;
 }
+
+/* linux_nat_new_fork hook.   */
+
+static void
+i386_linux_new_fork (struct lwp_info *parent, pid_t child_pid)
+{
+  pid_t parent_pid;
+  struct i386_debug_reg_state *parent_state;
+  struct i386_debug_reg_state *child_state;
+
+  /* NULL means no watchpoint has ever been set in the parent.  In
+     that case, there's nothing to do.  */
+  if (parent->arch_private == NULL)
+    return;
+
+  /* Linux kernel before 2.6.33 commit
+     72f674d203cd230426437cdcf7dd6f681dad8b0d
+     will inherit hardware debug registers from parent
+     on fork/vfork/clone.  Newer Linux kernels create such tasks with
+     zeroed debug registers.
+
+     GDB core assumes the child inherits the watchpoints/hw
+     breakpoints of the parent, and will remove them all from the
+     forked off process.  Copy the debug registers mirrors into the
+     new process so that all breakpoints and watchpoints can be
+     removed together.  The debug registers mirror will become zeroed
+     in the end before detaching the forked off process, thus making
+     this compatible with older Linux kernels too.  */
+
+  parent_pid = ptid_get_pid (parent->ptid);
+  parent_state = i386_debug_reg_state (parent_pid);
+  child_state = i386_debug_reg_state (child_pid);
+  *child_state = *parent_state;
+}
+
 
 
 /* Called by libthread_db.  Returns a pointer to the thread local
@@ -1044,5 +1082,7 @@ _initialize_i386_linux_nat (void)
   /* Register the target.  */
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, i386_linux_new_thread);
+  linux_nat_set_new_fork (t, i386_linux_new_fork);
+  linux_nat_set_forget_process (t, i386_forget_process);
   linux_nat_set_prepare_to_resume (t, i386_linux_prepare_to_resume);
 }
diff --git a/gdb/i386-nat.c b/gdb/i386-nat.c
index c87e7537f31..0a5deb06ca1 100644
--- a/gdb/i386-nat.c
+++ b/gdb/i386-nat.c
@@ -153,104 +153,102 @@ struct i386_dr_low_type i386_dr_low;
 /* A macro to loop over all debug registers.  */
 #define ALL_DEBUG_REGISTERS(i)	for (i = 0; i < DR_NADDR; i++)
 
-/* Clear the reference counts and forget everything we knew about the
-   debug registers.  */
+/* Per-process data.  We don't bind this to a per-inferior registry
+   because of targets like x86 GNU/Linux that need to keep track of
+   processes that aren't bound to any inferior (e.g., fork children,
+   checkpoints).  */
 
-static void
-i386_init_dregs (struct i386_debug_reg_state *state)
+struct i386_process_info
 {
-  int i;
-
-  ALL_DEBUG_REGISTERS (i)
-    {
-      state->dr_mirror[i] = 0;
-      state->dr_ref_count[i] = 0;
-    }
-  state->dr_control_mirror = 0;
-  state->dr_status_mirror  = 0;
-}
+  /* Linked list.  */
+  struct i386_process_info *next;
 
-/* Per-inferior data key.  */
-static const struct inferior_data *i386_inferior_data;
+  /* The process identifier.  */
+  pid_t pid;
 
-/* Per-inferior data.  */
-struct i386_inferior_data
-{
-  /* Copy of i386 hardware debug registers for performance reasons.  */
+  /* Copy of i386 hardware debug registers.  */
   struct i386_debug_reg_state state;
 };
 
-/* Per-inferior hook for register_inferior_data_with_cleanup.  */
+static struct i386_process_info *i386_process_list = NULL;
 
-static void
-i386_inferior_data_cleanup (struct inferior *inf, void *arg)
+/* Find process data for process PID.  */
+
+static struct i386_process_info *
+i386_find_process_pid (pid_t pid)
 {
-  struct i386_inferior_data *inf_data = arg;
+  struct i386_process_info *proc;
+
+  for (proc = i386_process_list; proc; proc = proc->next)
+    if (proc->pid == pid)
+      return proc;
 
-  xfree (inf_data);
+  return NULL;
 }
 
-/* Get data specific for INFERIOR_PTID LWP.  Return special data area
-   for processes being detached.  */
+/* Add process data for process PID.  Returns newly allocated info
+   object.  */
 
-static struct i386_inferior_data *
-i386_inferior_data_get (void)
+static struct i386_process_info *
+i386_add_process (pid_t pid)
 {
-  struct inferior *inf = current_inferior ();
-  struct i386_inferior_data *inf_data;
+  struct i386_process_info *proc;
 
-  inf_data = inferior_data (inf, i386_inferior_data);
-  if (inf_data == NULL)
-    {
-      inf_data = xzalloc (sizeof (*inf_data));
-      set_inferior_data (current_inferior (), i386_inferior_data, inf_data);
-    }
+  proc = xcalloc (1, sizeof (*proc));
+  proc->pid = pid;
 
-  if (inf->pid != ptid_get_pid (inferior_ptid))
-    {
-      /* INFERIOR_PTID is being detached from the inferior INF.
-	 Provide local cache specific for the detached LWP.  */
+  proc->next = i386_process_list;
+  i386_process_list = proc;
 
-      static struct i386_inferior_data detached_inf_data_local;
-      static int detached_inf_pid = -1;
+  return proc;
+}
 
-      if (detached_inf_pid != ptid_get_pid (inferior_ptid))
-	{
-	  /* Reinitialize the local cache if INFERIOR_PTID is
-	     different from the LWP last detached.
- 
-	     Linux kernel before 2.6.33 commit
-	     72f674d203cd230426437cdcf7dd6f681dad8b0d
-	     will inherit hardware debug registers from parent
-	     on fork/vfork/clone.  Newer Linux kernels create such tasks with
-	     zeroed debug registers.
-
-	     GDB will remove all breakpoints (and watchpoints) from the forked
-	     off process.  We also need to reset the debug registers in that
-	     process to be compatible with the older Linux kernels.
-
-	     Copy the debug registers mirrors into the new process so that all
-	     breakpoints and watchpoints can be removed together.  The debug
-	     registers mirror will become zeroed in the end before detaching
-	     the forked off process.  */
-
-	  detached_inf_pid = ptid_get_pid (inferior_ptid);
-	  detached_inf_data_local = *inf_data;
-	}
+/* Get data specific info for process PID, creating it if necessary.
+   Never returns NULL.  */
 
-      return &detached_inf_data_local;
-    }
+static struct i386_process_info *
+i386_process_info_get (pid_t pid)
+{
+  struct i386_process_info *proc;
+
+  proc = i386_find_process_pid (pid);
+  if (proc == NULL)
+    proc = i386_add_process (pid);
 
-  return inf_data;
+  return proc;
 }
 
-/* Get debug registers state for INFERIOR_PTID, see
-   i386_inferior_data_get.  */
+/* Get debug registers state for process PID.  */
 
 struct i386_debug_reg_state *
-i386_debug_reg_state (void)
+i386_debug_reg_state (pid_t pid)
 {
-  return &i386_inferior_data_get ()->state;
+  return &i386_process_info_get (pid)->state;
+}
+
+/* See declaration in i386-nat.h.  */
+
+void
+i386_forget_process (pid_t pid)
+{
+  struct i386_process_info *proc, **proc_link;
+
+  proc = i386_process_list;
+  proc_link = &i386_process_list;
+
+  while (proc != NULL)
+    {
+      if (proc->pid == pid)
+	{
+	  *proc_link = proc->next;
+
+	  xfree (proc);
+	  return;
+	}
+
+      proc_link = &proc->next;
+      proc = *proc_link;
+    }
 }
 
 /* Whether or not to print the mirrored debug registers.  */
@@ -303,9 +301,8 @@ static int i386_handle_nonaligned_watchpoint (struct i386_debug_reg_state *state
 void
 i386_cleanup_dregs (void)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
-
-  i386_init_dregs (state);
+  /* Starting from scratch has the same effect.  */
+  i386_forget_process (ptid_get_pid (inferior_ptid));
 }
 
 /* Print the values of the mirrored debug registers.  This is called
@@ -569,7 +566,8 @@ Invalid value %d of operation in i386_handle_nonaligned_watchpoint.\n"),
 static void
 i386_update_inferior_debug_regs (struct i386_debug_reg_state *new_state)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   int i;
 
   ALL_DEBUG_REGISTERS (i)
@@ -594,7 +592,8 @@ static int
 i386_insert_watchpoint (CORE_ADDR addr, int len, int type,
 			struct expression *cond)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   int retval;
   /* Work on a local copy of the debug registers, and on success,
      commit the change back to the inferior.  */
@@ -631,7 +630,8 @@ static int
 i386_remove_watchpoint (CORE_ADDR addr, int len, int type,
 			struct expression *cond)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   int retval;
   /* Work on a local copy of the debug registers, and on success,
      commit the change back to the inferior.  */
@@ -664,7 +664,8 @@ i386_remove_watchpoint (CORE_ADDR addr, int len, int type,
 static int
 i386_region_ok_for_watchpoint (CORE_ADDR addr, int len)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   int nregs;
 
   /* Compute how many aligned watchpoints we would need to cover this
@@ -681,7 +682,8 @@ i386_region_ok_for_watchpoint (CORE_ADDR addr, int len)
 static int
 i386_stopped_data_address (struct target_ops *ops, CORE_ADDR *addr_p)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   CORE_ADDR addr = 0;
   int i;
   int rc = 0;
@@ -766,7 +768,8 @@ static int
 i386_insert_hw_breakpoint (struct gdbarch *gdbarch,
 			   struct bp_target_info *bp_tgt)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   unsigned len_rw = i386_length_and_rw_bits (1, hw_execute);
   CORE_ADDR addr = bp_tgt->placed_address;
   /* Work on a local copy of the debug registers, and on success,
@@ -791,7 +794,8 @@ static int
 i386_remove_hw_breakpoint (struct gdbarch *gdbarch,
 			   struct bp_target_info *bp_tgt)
 {
-  struct i386_debug_reg_state *state = i386_debug_reg_state ();
+  struct i386_debug_reg_state *state
+    = i386_debug_reg_state (ptid_get_pid (inferior_ptid));
   unsigned len_rw = i386_length_and_rw_bits (1, hw_execute);
   CORE_ADDR addr = bp_tgt->placed_address;
   /* Work on a local copy of the debug registers, and on success,
@@ -869,10 +873,6 @@ i386_use_watchpoints (struct target_ops *t)
   t->to_remove_watchpoint = i386_remove_watchpoint;
   t->to_insert_hw_breakpoint = i386_insert_hw_breakpoint;
   t->to_remove_hw_breakpoint = i386_remove_hw_breakpoint;
-
-  if (i386_inferior_data == NULL)
-    i386_inferior_data
-      = register_inferior_data_with_cleanup (NULL, i386_inferior_data_cleanup);
 }
 
 void
diff --git a/gdb/i386-nat.h b/gdb/i386-nat.h
index 87e313df929..9ce52ab91ae 100644
--- a/gdb/i386-nat.h
+++ b/gdb/i386-nat.h
@@ -110,9 +110,14 @@ extern void i386_set_debug_register_length (int len);
 
 extern void i386_cleanup_dregs (void);
 
-/* Return a pointer to the the local mirror of the inferior's debug
-   registers.  */
+/* Return a pointer to the local mirror of the debug registers of
+   process PID.  */
 
-extern struct i386_debug_reg_state *i386_debug_reg_state (void);
+extern struct i386_debug_reg_state *i386_debug_reg_state (pid_t pid);
+
+/* Called whenever GDB is no longer debugging process PID.  It deletes
+   data structures that keep track of debug register state.  */
+
+extern void i386_forget_process (pid_t pid);
 
 #endif /* I386_NAT_H */
diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 21514011cdf..7ed1803fc76 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -122,6 +122,8 @@ delete_fork (ptid_t ptid)
 
   fpprev = NULL;
 
+  linux_nat_forget_process (ptid_get_pid (ptid));
+
   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
     if (ptid_equal (fp->ptid, ptid))
       break;
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 57bca111119..0713edd4451 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -184,6 +184,13 @@ static struct target_ops linux_ops_saved;
 /* The method to call, if any, when a new thread is attached.  */
 static void (*linux_nat_new_thread) (struct lwp_info *);
 
+/* The method to call, if any, when a new fork is attached.  */
+static linux_nat_new_fork_ftype *linux_nat_new_fork;
+
+/* The method to call, if any, when a process is no longer
+   attached.  */
+static linux_nat_forget_process_ftype *linux_nat_forget_process_hook;
+
 /* Hook to call prior to resuming a thread.  */
 static void (*linux_nat_prepare_to_resume) (struct lwp_info *);
 
@@ -698,15 +705,6 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 	  child_lp->last_resume_kind = resume_stop;
 	  make_cleanup (delete_lwp_cleanup, child_lp);
 
-	  /* CHILD_LP has new PID, therefore linux_nat_new_thread is not called for it.
-	     See i386_inferior_data_get for the Linux kernel specifics.
-	     Ensure linux_nat_prepare_to_resume will reset the hardware debug
-	     registers.  It is done by the linux_nat_new_thread call, which is
-	     being skipped in add_lwp above for the first lwp of a pid.  */
-	  gdb_assert (num_lwps (GET_PID (child_lp->ptid)) == 1);
-	  if (linux_nat_new_thread != NULL)
-	    linux_nat_new_thread (child_lp);
-
 	  if (linux_nat_prepare_to_resume != NULL)
 	    linux_nat_prepare_to_resume (child_lp);
 	  ptrace (PTRACE_DETACH, child_pid, 0, 0);
@@ -1176,12 +1174,22 @@ purge_lwp_list (int pid)
     }
 }
 
-/* Add the LWP specified by PID to the list.  Return a pointer to the
-   structure describing the new LWP.  The LWP should already be stopped
-   (with an exception for the very first LWP).  */
+/* Add the LWP specified by PTID to the list.  PTID is the first LWP
+   in the process.  Return a pointer to the structure describing the
+   new LWP.
+
+   This differs from add_lwp in that we don't let the arch specific
+   bits know about this new thread.  Current clients of this callback
+   take the opportunity to install watchpoints in the new thread, and
+   we shouldn't do that for the first thread.  If we're spawning a
+   child ("run"), the thread executes the shell wrapper first, and we
+   shouldn't touch it until it execs the program we want to debug.
+   For "attach", it'd be okay to call the callback, but it's not
+   necessary, because watchpoints can't yet have been inserted into
+   the inferior.  */
 
 static struct lwp_info *
-add_lwp (ptid_t ptid)
+add_initial_lwp (ptid_t ptid)
 {
   struct lwp_info *lp;
 
@@ -1200,15 +1208,25 @@ add_lwp (ptid_t ptid)
   lp->next = lwp_list;
   lwp_list = lp;
 
+  return lp;
+}
+
+/* Add the LWP specified by PID to the list.  Return a pointer to the
+   structure describing the new LWP.  The LWP should already be
+   stopped.  */
+
+static struct lwp_info *
+add_lwp (ptid_t ptid)
+{
+  struct lwp_info *lp;
+
+  lp = add_initial_lwp (ptid);
+
   /* Let the arch specific bits know about this new thread.  Current
      clients of this callback take the opportunity to install
-     watchpoints in the new thread.  Don't do this for the first
-     thread though.  If we're spawning a child ("run"), the thread
-     executes the shell wrapper first, and we shouldn't touch it until
-     it execs the program we want to debug.  For "attach", it'd be
-     okay to call the callback, but it's not necessary, because
-     watchpoints can't yet have been inserted into the inferior.  */
-  if (num_lwps (GET_PID (ptid)) > 1 && linux_nat_new_thread != NULL)
+     watchpoints in the new thread.  We don't do this for the first
+     thread though.  See add_initial_lwp.  */
+  if (linux_nat_new_thread != NULL)
     linux_nat_new_thread (lp);
 
   return lp;
@@ -1285,45 +1303,6 @@ iterate_over_lwps (ptid_t filter,
   return NULL;
 }
 
-/* Iterate like iterate_over_lwps does except when forking-off a child call
-   CALLBACK with CALLBACK_DATA specifically only for that new child PID.  */
-
-void
-linux_nat_iterate_watchpoint_lwps
-  (linux_nat_iterate_watchpoint_lwps_ftype callback, void *callback_data)
-{
-  int inferior_pid = ptid_get_pid (inferior_ptid);
-  struct inferior *inf = current_inferior ();
-
-  if (inf->pid == inferior_pid)
-    {
-      /* Iterate all the threads of the current inferior.  Without specifying
-	 INFERIOR_PID it would iterate all threads of all inferiors, which is
-	 inappropriate for watchpoints.  */
-
-      iterate_over_lwps (pid_to_ptid (inferior_pid), callback, callback_data);
-    }
-  else
-    {
-      /* Detaching a new child PID temporarily present in INFERIOR_PID.  */
-
-      struct lwp_info *child_lp;
-      struct cleanup *old_chain;
-      pid_t child_pid = GET_PID (inferior_ptid);
-      ptid_t child_ptid = ptid_build (child_pid, child_pid, 0);
-
-      gdb_assert (find_lwp_pid (child_ptid) == NULL);
-      child_lp = add_lwp (child_ptid);
-      child_lp->stopped = 1;
-      child_lp->last_resume_kind = resume_stop;
-      old_chain = make_cleanup (delete_lwp_cleanup, child_lp);
-
-      callback (child_lp, callback_data);
-
-      do_cleanups (old_chain);
-    }
-}
-
 /* 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
@@ -1656,7 +1635,7 @@ linux_nat_attach (struct target_ops *ops, char *args, int from_tty)
   thread_change_ptid (inferior_ptid, ptid);
 
   /* Add the initial process as the first LWP to the list.  */
-  lp = add_lwp (ptid);
+  lp = add_initial_lwp (ptid);
 
   status = linux_nat_post_attach_wait (lp->ptid, 1, &lp->cloned,
 				       &lp->signalled);
@@ -2309,6 +2288,15 @@ linux_handle_extended_wait (struct lwp_info *lp, int status,
 
       ourstatus->value.related_pid = ptid_build (new_pid, new_pid, 0);
 
+      if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK)
+	{
+	  /* The arch-specific native code may need to know about new
+	     forks even if those end up never mapped to an
+	     inferior.  */
+	  if (linux_nat_new_fork != NULL)
+	    linux_nat_new_fork (lp, new_pid);
+	}
+
       if (event == PTRACE_EVENT_FORK
 	  && linux_fork_checkpointing_p (GET_PID (lp->ptid)))
 	{
@@ -3489,7 +3477,7 @@ linux_nat_wait_1 (struct target_ops *ops,
 			  BUILD_LWP (GET_PID (inferior_ptid),
 				     GET_PID (inferior_ptid)));
 
-      lp = add_lwp (inferior_ptid);
+      lp = add_initial_lwp (inferior_ptid);
       lp->resumed = 1;
     }
 
@@ -4075,6 +4063,10 @@ linux_nat_kill (struct target_ops *ops)
     {
       ptrace (PT_KILL, PIDGET (last.value.related_pid), 0, 0);
       wait (&status);
+
+      /* Let the arch-specific native code know this process is
+	 gone.  */
+      linux_nat_forget_process (PIDGET (last.value.related_pid));
     }
 
   if (forks_exist_p ())
@@ -4103,7 +4095,9 @@ linux_nat_kill (struct target_ops *ops)
 static void
 linux_nat_mourn_inferior (struct target_ops *ops)
 {
-  purge_lwp_list (ptid_get_pid (inferior_ptid));
+  int pid = ptid_get_pid (inferior_ptid);
+
+  purge_lwp_list (pid);
 
   if (! forks_exist_p ())
     /* Normal case, no other forks available.  */
@@ -4113,6 +4107,9 @@ linux_nat_mourn_inferior (struct target_ops *ops)
        there are other viable forks to debug.  Delete the exiting
        one and context-switch to the first available.  */
     linux_fork_mourn_inferior ();
+
+  /* Let the arch-specific native code know this process is gone.  */
+  linux_nat_forget_process (pid);
 }
 
 /* Convert a native/host siginfo object, into/from the siginfo in the
@@ -5146,6 +5143,35 @@ linux_nat_set_new_thread (struct target_ops *t,
   linux_nat_new_thread = new_thread;
 }
 
+/* See declaration in linux-nat.h.  */
+
+void
+linux_nat_set_new_fork (struct target_ops *t,
+			linux_nat_new_fork_ftype *new_fork)
+{
+  /* Save the pointer.  */
+  linux_nat_new_fork = new_fork;
+}
+
+/* See declaration in linux-nat.h.  */
+
+void
+linux_nat_set_forget_process (struct target_ops *t,
+			      linux_nat_forget_process_ftype *fn)
+{
+  /* Save the pointer.  */
+  linux_nat_forget_process_hook = fn;
+}
+
+/* See declaration in linux-nat.h.  */
+
+void
+linux_nat_forget_process (pid_t pid)
+{
+  if (linux_nat_forget_process_hook != NULL)
+    linux_nat_forget_process_hook (pid);
+}
+
 /* Register a method that converts a siginfo object between the layout
    that ptrace returns, and the layout in the architecture of the
    inferior.  */
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index 928721b2462..3de866d5ed3 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -154,12 +154,6 @@ struct lwp_info *iterate_over_lwps (ptid_t filter,
 						     void *), 
 				    void *data);
 
-typedef int (*linux_nat_iterate_watchpoint_lwps_ftype) (struct lwp_info *lwp,
-							void *arg);
-
-extern void linux_nat_iterate_watchpoint_lwps
-  (linux_nat_iterate_watchpoint_lwps_ftype callback, void *callback_data);
-
 /* Create a prototype generic GNU/Linux target.  The client can
    override it with local methods.  */
 struct target_ops * linux_target (void);
@@ -176,6 +170,23 @@ void linux_nat_add_target (struct target_ops *);
 /* Register a method to call whenever a new thread is attached.  */
 void linux_nat_set_new_thread (struct target_ops *, void (*) (struct lwp_info *));
 
+
+/* Register a method to call whenever a new fork is attached.  */
+typedef void (linux_nat_new_fork_ftype) (struct lwp_info *parent,
+					 pid_t child_pid);
+void linux_nat_set_new_fork (struct target_ops *ops,
+			     linux_nat_new_fork_ftype *fn);
+
+/* Register a method to call whenever a process is killed or
+   detached.  */
+typedef void (linux_nat_forget_process_ftype) (pid_t pid);
+void linux_nat_set_forget_process (struct target_ops *ops,
+				   linux_nat_forget_process_ftype *fn);
+
+/* Call the method registered with the function above.  PID is the
+   process to forget about.  */
+void linux_nat_forget_process (pid_t pid);
+
 /* Register a method that converts a siginfo object between the layout
    that ptrace returns, and the layout in the architecture of the
    inferior.  */
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 7ef10f1045a..2fe50b1d34e 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -1881,6 +1881,7 @@ windows_detach (struct target_ops *ops, char *args, int from_tty)
       gdb_flush (gdb_stdout);
     }
 
+  i386_cleanup_dregs ();
   inferior_ptid = null_ptid;
   detach_inferior (current_event.dwProcessId);