[RFA 5/7 take 2] Improved linker-debugger interface

[Gary Benson <gbenson@redhat.com>]

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All issues not explicitly replied to below have been fixed as
suggested.

Jan Kratochvil wrote:
> On Thu, 16 May 2013 16:48:38 +0200, Gary Benson wrote:
> > diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
> > index 4e09472..6b4bdb0 100644
> [...]
> > -/* Implement the "current_sos" target_so_ops method.  */
> > +/* Read the full list of currently loaded shared objects directly from
> > +   the inferior.  */
> >  
> >  static struct so_list *
> > -svr4_current_sos (void)
> > +svr4_current_sos_direct (struct svr4_info *info)
> 
> Meaning of 'direct' seems ambiguous/unclear to me, maybe 'uncached'?
> Just a hint, OK even with 'direct'.

Naming this function was the final thing I did before mailing the
original patch... it has been svr4_current_sos_XXX for some time :)

When I started writing the incremental code I thought of the solibs
as being cached by GDB, but a few versions later I didn't like the
terminology and renamed all the variables.   The stuff about caching
in the comments here was a hangover from that.

What I've done in the attached patch is to update the comments so
they don't mention caching.  This should hopefully make what is
happening clearer.  I've left the name as "direct" here, though
only because I can't think of anything better--I'm not especially
happy with the name myself.

Would "svr4_current_sos_1" be acceptable, or is the "_1" naming
discouraged?

> > +/* Populate the shared object list by reading the entire list of
> > +   shared objects from the inferior.  Returns nonzero on success.  */
> > +
> > +static int
> > +solist_update_full (struct svr4_info *info)
> > +{
> > +  svr4_free_library_list (&info->solib_list);
> 
> I find it a bit fragily this way, I would find worth it here also:
>   info->solib_list = NULL;
> 
> As svr4_current_sos_direct is a pretty big function and it could
> somehow check/update even info->solib_list possibly in the future.
> 
> Maybe a matter of opinion a bit.

That's a good idea and I've implemented it.

> > +/* Update the shared object list starting from the link-map entry
> > +   passed by the linker in the probe's third argument.  Returns
> > +   nonzero if the list was successfully updated, or zero to indicate
> > +   failure.  */
> > +
> > +static int
> > +solist_update_incremental (struct svr4_info *info, CORE_ADDR lm)
> > +{
> > +  struct so_list *tail;
> > +  CORE_ADDR prev_lm;
> > +
> > +  /* Fall back to a full update if we haven't read anything yet.  */
> > +  if (info->solib_list == NULL)
> > +    return 0;
> > +
> > +  /* Fall back to a full update if we are using a remote target
> > +     that does not support incremental transfers.  */
> > +  if (info->using_xfer && !target_augmented_libraries_svr4_read())
> > +    return 0;
> > +
> > +  /* Walk to the end of the list.  */
> > +  for (tail = info->solib_list; tail->next; tail = tail->next);
[...]
> > +  prev_lm = tail->lm_info->lm_addr;
> > +
> > +  /* Read the new objects.  */
> > +  if (info->using_xfer)
> > +    {
> > +      struct svr4_library_list library_list;
> > +      char annex[64];
> > +
> > +      xsnprintf (annex, sizeof (annex), "start=%lx;prev=%lx", lm, prev_lm);
[...]
> > +      if (!svr4_current_sos_via_xfer_libraries (&library_list, annex))
> > +	return 0;
> > +
> > +      tail->next = library_list.head;
> > +    }
> > +  else
> > +    {
> > +      struct so_list **link = &tail->next;
> > +
> > +      if (!svr4_read_so_list (lm, prev_lm, &link, 0))
> 
> You should set the last IGNORE_FIRST parameter properly.  While
> glibc has "" there AFAIK some OSes like Solaris may have some valid
> pathname there which would confuse GDB listing the executable also
> as a shared library.

I set IGNORE_FIRST to zero here because for this particular call
svr4_read_so_list never sees the first element in the list.  If
solist_update_incremental is called at the top of the list then
the "if (info->solib_list == NULL) return 0;" at the top of
solist_update_incremental causes it to defer to solist_update_full.
That uses svr4_current_sos_direct, which does set IGNORE_FIRST
correctly.

> > +static void
> > +svr4_handle_solib_event (void)
> > +{
[...]
> 
> You could just always do { do_cleanups; return; } IMO and avoid the
> goto but up to you.

I have done this.  The original code after the goto was more complex,
but now it is a single line this is a no-brainer.

> > +static int
> > +svr4_update_solib_event_breakpoint (struct breakpoint *b, void *arg)
> > +{
[...]
> 
> It seems a bit suspicious that no update_global_location_list* is
> called.  Why is it safe?

I didn't know about update_global_location_list.  I've updated this
code to use enable_breakpoint and disable_breakpoint.

> > @@ -1460,6 +2032,8 @@ enable_break (struct svr4_info *info, int from_tty)
> >    info->interp_text_sect_low = info->interp_text_sect_high = 0;
> >    info->interp_plt_sect_low = info->interp_plt_sect_high = 0;
> >  
> > +  free_probes_table (info);
> 
> Why is this one needed and free_solib_list is not needed?

free_solib_list is called in svr4_solib_create_inferior_hook.
I originally had the two calls together, in enable_break, but
doing it that way caused breakpoint resetting errors when the
inferior was restarted.  There is a check for this in
info-shared.exp.

Thanks,
Gary

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2013-05-23  Gary Benson  <gbenson@redhat.com>

	* breakpoint.h (handle_solib_event): Moved function declaration
	to solib.h.
	* breakpoint.c (handle_solib_event): Moved function to solib.c.
	(bpstat_stop_status): Pass new argument to handle_solib_event.
	* solib.h (update_solib_breakpoints): New function declaration.
	(handle_solib_event): Moved function declaration from
	breakpoint.h.
	* solib.c (update_solib_breakpoints): New function.
	(handle_solib_event): Moved function from breakpoint.c.
	Updated to call solib_ops->handle_event if not NULL.
	* solist.h (target_so_ops): New fields "update_breakpoints" and
	"handle_event".
	* infrun.c (set_stop_on_solib_events): New function.
	(_initialize_infrun): Use the above for "set
	stop-on-solib-events".
	(handle_inferior_event): Pass new argument to handle_solib_event.
	* solib-svr4.c (probe.h): New include.
	(svr4_free_library_list): New forward declaration.
	(probe_action): New enum.
	(probe_info): New struct.
	(probe_info): New static variable.
	(NUM_PROBES): New definition.
	(svr4_info): New fields "using_xfer", "probes_table" and
	"solib_list".
	(free_probes_table): New function.
	(free_solib_list): New function.
	(svr4_pspace_data_cleanup): Free probes table and solib list.
	(svr4_copy_library_list): New function.
	(svr4_current_sos_via_xfer_libraries): New parameter "annex".
	(svr4_read_so_list): New parameter "prev_lm".
	(svr4_current_sos_direct): Renamed from "svr4_current_sos".
	(svr4_current_sos): New function.
	(probe_and_action): New struct.
	(hash_probe_and_action): New function.
	(equal_probe_and_action): Likewise.
	(register_solib_event_probe): Likewise.
	(solib_event_probe_at): Likewise.
	(solib_event_probe_action): Likewise.
	(solist_update_full): Likewise.
	(solist_update_incremental): Likewise.
	(disable_probes_interface_cleanup): Likewise.
	(svr4_handle_solib_event): Likewise.
	(svr4_update_solib_event_breakpoint): Likewise.
	(svr4_update_solib_event_breakpoints): Likewise.
	(svr4_create_solib_event_breakpoints): Likewise.
	(enable_break): Free probes table before creating breakpoints.
	Use svr4_create_solib_event_breakpoints to create breakpoints.
	(svr4_solib_create_inferior_hook): Free the solib list.
	(_initialize_svr4_solib): Initialise
	svr4_so_ops.handle_solib_event and svr4_so_ops.update_breakpoints.

diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 7df1122..e996e54 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -1553,8 +1553,6 @@ extern int user_breakpoint_p (struct breakpoint *);
 /* Attempt to determine architecture of location identified by SAL.  */
 extern struct gdbarch *get_sal_arch (struct symtab_and_line sal);
 
-extern void handle_solib_event (void);
-
 extern void breakpoint_free_objfile (struct objfile *objfile);
 
 extern char *ep_parse_optional_if_clause (char **arg);
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index f4f9325..639ddae 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -5343,21 +5343,6 @@ handle_jit_event (void)
   target_terminal_inferior ();
 }
 
-/* Handle an solib event by calling solib_add.  */
-
-void
-handle_solib_event (void)
-{
-  clear_program_space_solib_cache (current_inferior ()->pspace);
-
-  /* Check for any newly added shared libraries if we're supposed to
-     be adding them automatically.  Switch terminal for any messages
-     produced by breakpoint_re_set.  */
-  target_terminal_ours_for_output ();
-  solib_add (NULL, 0, &current_target, auto_solib_add);
-  target_terminal_inferior ();
-}
-
 /* Prepare WHAT final decision for infrun.  */
 
 /* Decide what infrun needs to do with this bpstat.  */
diff --git a/gdb/solib.h b/gdb/solib.h
index b811866..2108429 100644
--- a/gdb/solib.h
+++ b/gdb/solib.h
@@ -90,4 +90,12 @@ extern CORE_ADDR gdb_bfd_lookup_symbol_from_symtab (bfd *abfd,
 								      void *),
 						    void *data);
 
+/* Enable or disable optional solib event breakpoints as appropriate.  */
+
+extern void update_solib_breakpoints (void);
+
+/* Handle an solib event by calling solib_add.  */
+
+extern void handle_solib_event (void);
+
 #endif /* SOLIB_H */
diff --git a/gdb/solib.c b/gdb/solib.c
index a3479c5..763b93c 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -1208,6 +1208,37 @@ no_shared_libraries (char *ignored, int from_tty)
   objfile_purge_solibs ();
 }
 
+/* See solib.h.  */
+
+void
+update_solib_breakpoints (void)
+{
+  const struct target_so_ops *ops = solib_ops (target_gdbarch ());
+
+  if (ops->update_breakpoints != NULL)
+    ops->update_breakpoints ();
+}
+
+/* See solib.h.  */
+
+void
+handle_solib_event (void)
+{
+  const struct target_so_ops *ops = solib_ops (target_gdbarch ());
+
+  if (ops->handle_event != NULL)
+    ops->handle_event ();
+
+  clear_program_space_solib_cache (current_inferior ()->pspace);
+
+  /* Check for any newly added shared libraries if we're supposed to
+     be adding them automatically.  Switch terminal for any messages
+     produced by breakpoint_re_set.  */
+  target_terminal_ours_for_output ();
+  solib_add (NULL, 0, &current_target, auto_solib_add);
+  target_terminal_inferior ();
+}
+
 /* Reload shared libraries, but avoid reloading the same symbol file
    we already have loaded.  */
 
diff --git a/gdb/solist.h b/gdb/solist.h
index 0495474..244484a 100644
--- a/gdb/solist.h
+++ b/gdb/solist.h
@@ -153,6 +153,19 @@ struct target_so_ops
        core file (in particular, for readonly sections).  */
     int (*keep_data_in_core) (CORE_ADDR vaddr,
 			      unsigned long size);
+
+    /* Enable or disable optional solib event breakpoints as
+       appropriate.  This should be called whenever
+       stop_on_solib_events is changed.  This pointer can be
+       NULL, in which case no enabling or disabling is necessary
+       for this target.  */
+    void (*update_breakpoints) (void);
+
+    /* Target-specific processing of solib events that will be
+       performed before solib_add is called.  This pointer can be
+       NULL, in which case no specific preprocessing is necessary
+       for this target.  */
+    void (*handle_event) (void);
   };
 
 /* Free the memory associated with a (so_list *).  */
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 54e92f2..a020dd6 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -370,6 +370,16 @@ static struct symbol *step_start_function;
 /* Nonzero if we want to give control to the user when we're notified
    of shared library events by the dynamic linker.  */
 int stop_on_solib_events;
+
+/* Enable or disable optional shared library event breakpoints
+   as appropriate when the above flag is changed.  */
+
+static void
+set_stop_on_solib_events (char *args, int from_tty, struct cmd_list_element *c)
+{
+  update_solib_breakpoints ();
+}
+
 static void
 show_stop_on_solib_events (struct ui_file *file, int from_tty,
 			   struct cmd_list_element *c, const char *value)
@@ -7303,7 +7313,7 @@ Show stopping for shared library events."), _("\
 If nonzero, gdb will give control to the user when the dynamic linker\n\
 notifies gdb of shared library events.  The most common event of interest\n\
 to the user would be loading/unloading of a new library."),
-			    NULL,
+			    set_stop_on_solib_events,
 			    show_stop_on_solib_events,
 			    &setlist, &showlist);
 
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 055fcb7..066b5f9 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -46,10 +46,12 @@
 #include "auxv.h"
 #include "exceptions.h"
 #include "gdb_bfd.h"
+#include "probe.h"
 
 static struct link_map_offsets *svr4_fetch_link_map_offsets (void);
 static int svr4_have_link_map_offsets (void);
 static void svr4_relocate_main_executable (void);
+static void svr4_free_library_list (void *p_list);
 
 /* Link map info to include in an allocated so_list entry.  */
 
@@ -106,6 +108,55 @@ static const  char * const main_name_list[] =
   NULL
 };
 
+/* What to do when a probe stop occurs.  */
+
+enum probe_action
+{
+  /* Something went seriously wrong.  Stop using probes and
+     revert to using the older interface.  */
+  PROBES_INTERFACE_FAILED,
+
+  /* No action is required.  The shared object list is still
+     valid.  */
+  DO_NOTHING,
+
+  /* The shared object list should be reloaded entirely.  */
+  FULL_RELOAD,
+
+  /* Attempt to incrementally update the shared object list. If
+     the update fails or is not possible, fall back to reloading
+     the list in full.  */
+  UPDATE_OR_RELOAD,
+};
+
+/* A probe's name and its associated action.  */
+
+struct probe_info
+{
+  /* The name of the probe.  */
+  const char *name;
+
+  /* What to do when a probe stop occurs.  */
+  enum probe_action action;
+};
+
+/* A list of named probes and their associated actions.  If all
+   probes are present in the dynamic linker then the probes-based
+   interface will be used.  */
+
+static const struct probe_info probe_info[] =
+{
+  { "init_start", DO_NOTHING },
+  { "init_complete", FULL_RELOAD },
+  { "map_start", DO_NOTHING },
+  { "map_failed", DO_NOTHING },
+  { "reloc_complete", UPDATE_OR_RELOAD },
+  { "unmap_start", DO_NOTHING },
+  { "unmap_complete", FULL_RELOAD },
+};
+
+#define NUM_PROBES ARRAY_SIZE (probe_info)
+
 /* Return non-zero if GDB_SO_NAME and INFERIOR_SO_NAME represent
    the same shared library.  */
 
@@ -313,17 +364,58 @@ struct svr4_info
   CORE_ADDR interp_text_sect_high;
   CORE_ADDR interp_plt_sect_low;
   CORE_ADDR interp_plt_sect_high;
+
+  /* Nonzero if the list of objects was last obtained from the target
+     via qXfer:libraries-svr4:read.  */
+  int using_xfer;
+
+  /* Table of struct probe_and_action instances, used by the
+     probes-based interface to map breakpoint addresses to probes
+     and their associated actions.  Lookup is performed using
+     probe_and_action->probe->address.  */
+  htab_t probes_table;
+
+  /* List of objects loaded into the inferior, used by the probes-
+     based interface.  */
+  struct so_list *solib_list;
 };
 
 /* Per-program-space data key.  */
 static const struct program_space_data *solib_svr4_pspace_data;
 
+/* Free the probes table.  */
+
+static void
+free_probes_table (struct svr4_info *info)
+{
+  if (info->probes_table == NULL)
+    return;
+
+  htab_delete (info->probes_table);
+  info->probes_table = NULL;
+}
+
+/* Free the solib list.  */
+
+static void
+free_solib_list (struct svr4_info *info)
+{
+  svr4_free_library_list (&info->solib_list);
+  info->solib_list = NULL;
+}
+
 static void
 svr4_pspace_data_cleanup (struct program_space *pspace, void *arg)
 {
   struct svr4_info *info;
 
   info = program_space_data (pspace, solib_svr4_pspace_data);
+  if (info == NULL)
+    return;
+
+  free_probes_table (info);
+  free_solib_list (info);
+
   xfree (info);
 }
 
@@ -991,6 +1083,37 @@ svr4_free_library_list (void *p_list)
     }
 }
 
+/* Copy library list.  */
+
+static struct so_list *
+svr4_copy_library_list (struct so_list *src)
+{
+  struct so_list *dst = NULL;
+  struct so_list **link = &dst;
+
+  while (src != NULL)
+    {
+      struct so_list *new;
+
+      new = xmalloc (sizeof (struct so_list));
+      memcpy (new, src, sizeof (struct so_list));
+
+      if (src->lm_info != NULL)
+	{
+	  new->lm_info = xmalloc (sizeof (struct lm_info));
+	  memcpy (new->lm_info, src->lm_info, sizeof (struct lm_info));
+	}
+
+      new->next = NULL;
+      *link = new;
+      link = &new->next;
+
+      src = src->next;
+    }
+
+  return dst;
+}
+
 #ifdef HAVE_LIBEXPAT
 
 #include "xml-support.h"
@@ -1106,23 +1229,30 @@ svr4_parse_libraries (const char *document, struct svr4_library_list *list)
   return 0;
 }
 
-/* Attempt to get so_list from target via qXfer:libraries:read packet.
+/* Attempt to get so_list from target via qXfer:libraries-svr4:read packet.
 
    Return 0 if packet not supported, *SO_LIST_RETURN is not modified in such
    case.  Return 1 if *SO_LIST_RETURN contains the library list, it may be
-   empty, caller is responsible for freeing all its entries.  */
+   empty, caller is responsible for freeing all its entries.
+
+   Note that ANNEX must be NULL if the remote does not explicitly allow
+   qXfer:libraries-svr4:read packets with non-empty annexes.  Support for
+   this can be checked using target_augmented_libraries_svr4_read ().  */
 
 static int
-svr4_current_sos_via_xfer_libraries (struct svr4_library_list *list)
+svr4_current_sos_via_xfer_libraries (struct svr4_library_list *list,
+				     const char *annex)
 {
   char *svr4_library_document;
   int result;
   struct cleanup *back_to;
 
+  gdb_assert (annex == NULL || target_augmented_libraries_svr4_read());
+
   /* Fetch the list of shared libraries.  */
   svr4_library_document = target_read_stralloc (&current_target,
 						TARGET_OBJECT_LIBRARIES_SVR4,
-						NULL);
+						annex);
   if (svr4_library_document == NULL)
     return 0;
 
@@ -1136,7 +1266,8 @@ svr4_current_sos_via_xfer_libraries (struct svr4_library_list *list)
 #else
 
 static int
-svr4_current_sos_via_xfer_libraries (struct svr4_library_list *list)
+svr4_current_sos_via_xfer_libraries (struct svr4_library_list *list,
+				     const char *annex)
 {
   return 0;
 }
@@ -1170,15 +1301,19 @@ svr4_default_sos (void)
   return new;
 }
 
-/* Read the whole inferior libraries chain starting at address LM.  Add the
-   entries to the tail referenced by LINK_PTR_PTR.  Ignore the first entry if
-   IGNORE_FIRST and set global MAIN_LM_ADDR according to it.  */
+/* Read the whole inferior libraries chain starting at address LM.
+   Expect the first entry in the chain's previous entry to be PREV_LM.
+   Add the entries to the tail referenced by LINK_PTR_PTR.  Ignore the
+   first entry if IGNORE_FIRST and set global MAIN_LM_ADDR according
+   to it.  Returns nonzero upon success.  If zero is returned the
+   entries stored to LINK_PTR_PTR are still valid although they may
+   represent only part of the inferior library list.  */
 
-static void
-svr4_read_so_list (CORE_ADDR lm, struct so_list ***link_ptr_ptr,
-		   int ignore_first)
+static int
+svr4_read_so_list (CORE_ADDR lm, CORE_ADDR prev_lm,
+		   struct so_list ***link_ptr_ptr, int ignore_first)
 {
-  CORE_ADDR prev_lm = 0, next_lm;
+  CORE_ADDR next_lm;
 
   for (; lm != 0; prev_lm = lm, lm = next_lm)
     {
@@ -1194,7 +1329,7 @@ svr4_read_so_list (CORE_ADDR lm, struct so_list ***link_ptr_ptr,
       if (new->lm_info == NULL)
 	{
 	  do_cleanups (old_chain);
-	  break;
+	  return 0;
 	}
 
       next_lm = new->lm_info->l_next;
@@ -1205,7 +1340,7 @@ svr4_read_so_list (CORE_ADDR lm, struct so_list ***link_ptr_ptr,
 		   paddress (target_gdbarch (), prev_lm),
 		   paddress (target_gdbarch (), new->lm_info->l_prev));
 	  do_cleanups (old_chain);
-	  break;
+	  return 0;
 	}
 
       /* For SVR4 versions, the first entry in the link map is for the
@@ -1251,17 +1386,20 @@ svr4_read_so_list (CORE_ADDR lm, struct so_list ***link_ptr_ptr,
       **link_ptr_ptr = new;
       *link_ptr_ptr = &new->next;
     }
+
+  return 1;
 }
 
-/* Implement the "current_sos" target_so_ops method.  */
+/* Read the full list of currently loaded shared objects directly
+   from the inferior, without referring to any libraries read and
+   stored by the probes interface.  */
 
 static struct so_list *
-svr4_current_sos (void)
+svr4_current_sos_direct (struct svr4_info *info)
 {
   CORE_ADDR lm;
   struct so_list *head = NULL;
   struct so_list **link_ptr = &head;
-  struct svr4_info *info;
   struct cleanup *back_to;
   int ignore_first;
   struct svr4_library_list library_list;
@@ -1274,19 +1412,16 @@ svr4_current_sos (void)
      Unfortunately statically linked inferiors will also fall back through this
      suboptimal code path.  */
 
-  if (svr4_current_sos_via_xfer_libraries (&library_list))
+  info->using_xfer = svr4_current_sos_via_xfer_libraries (&library_list,
+							  NULL);
+  if (info->using_xfer)
     {
       if (library_list.main_lm)
-	{
-	  info = get_svr4_info ();
-	  info->main_lm_addr = library_list.main_lm;
-	}
+	info->main_lm_addr = library_list.main_lm;
 
       return library_list.head ? library_list.head : svr4_default_sos ();
     }
 
-  info = get_svr4_info ();
-
   /* Always locate the debug struct, in case it has moved.  */
   info->debug_base = 0;
   locate_base (info);
@@ -1309,7 +1444,7 @@ svr4_current_sos (void)
      `struct so_list' nodes.  */
   lm = solib_svr4_r_map (info);
   if (lm)
-    svr4_read_so_list (lm, &link_ptr, ignore_first);
+    svr4_read_so_list (lm, 0, &link_ptr, ignore_first);
 
   /* On Solaris, the dynamic linker is not in the normal list of
      shared objects, so make sure we pick it up too.  Having
@@ -1317,7 +1452,7 @@ svr4_current_sos (void)
      for skipping dynamic linker resolver code.  */
   lm = solib_svr4_r_ldsomap (info);
   if (lm)
-    svr4_read_so_list (lm, &link_ptr, 0);
+    svr4_read_so_list (lm, 0, &link_ptr, 0);
 
   discard_cleanups (back_to);
 
@@ -1327,6 +1462,22 @@ svr4_current_sos (void)
   return head;
 }
 
+/* Implement the "current_sos" target_so_ops method.  */
+
+static struct so_list *
+svr4_current_sos (void)
+{
+  struct svr4_info *info = get_svr4_info ();
+
+  /* If the solib list has been read and stored by the probes
+     interface then we return a copy of the stored list.  */
+  if (info->solib_list != NULL)
+    return svr4_copy_library_list (info->solib_list);
+
+  /* Otherwise obtain the solib list directly from the inferior.  */
+  return svr4_current_sos_direct (info);
+}
+
 /* Get the address of the link_map for a given OBJFILE.  */
 
 CORE_ADDR
@@ -1409,6 +1560,467 @@ exec_entry_point (struct bfd *abfd, struct target_ops *targ)
   return gdbarch_addr_bits_remove (target_gdbarch (), addr);
 }
 
+/* A probe and its associated action.  */
+
+struct probe_and_action
+{
+  /* The probe.  */
+  struct probe *probe;
+
+  /* The action.  */
+  enum probe_action action;
+};
+
+/* Returns a hash code for the probe_and_action referenced by p.  */
+
+static hashval_t
+hash_probe_and_action (const void *p)
+{
+  const struct probe_and_action *pa = p;
+
+  return (hashval_t) pa->probe->address;
+}
+
+/* Returns non-zero if the probe_and_actions referenced by p1 and p2
+   are equal.  */
+
+static int
+equal_probe_and_action (const void *p1, const void *p2)
+{
+  const struct probe_and_action *pa1 = p1;
+  const struct probe_and_action *pa2 = p2;
+
+  return pa1->probe->address == pa2->probe->address;
+}
+
+/* Register a solib event probe and its associated action in the
+   probes table.  */
+
+static void
+register_solib_event_probe (struct probe *probe, enum probe_action action)
+{
+  struct svr4_info *info = get_svr4_info ();
+  struct probe_and_action lookup, *pa;
+  void **slot;
+
+  /* Create the probes table, if necessary.  */
+  if (info->probes_table == NULL)
+    info->probes_table = htab_create_alloc (1, hash_probe_and_action,
+					    equal_probe_and_action,
+					    xfree, xcalloc, xfree);
+
+  lookup.probe = probe;
+  slot = htab_find_slot (info->probes_table, &lookup, INSERT);
+  gdb_assert (*slot == HTAB_EMPTY_ENTRY);
+
+  pa = XCNEW (struct probe_and_action);
+  pa->probe = probe;
+  pa->action = action;
+
+  *slot = pa;
+}
+
+/* Get the solib event probe at the specified location, and the
+   action associated with it.  Returns NULL if no solib event probe
+   was found.  */
+
+static struct probe_and_action *
+solib_event_probe_at (struct svr4_info *info, CORE_ADDR address)
+{
+  struct probe lookup_probe;
+  struct probe_and_action lookup;
+  void **slot;
+
+  lookup_probe.address = address;
+  lookup.probe = &lookup_probe;
+  slot = htab_find_slot (info->probes_table, &lookup, NO_INSERT);
+
+  if (slot == NULL)
+    return NULL;
+
+  return (struct probe_and_action *) *slot;
+}
+
+/* Decide what action to take when the specified solib event probe is
+   hit.  */
+
+static enum probe_action
+solib_event_probe_action (struct probe_and_action *pa)
+{
+  enum probe_action action;
+  unsigned probe_argc;
+
+  action = pa->action;
+  if (action == DO_NOTHING || action == PROBES_INTERFACE_FAILED)
+    return action;
+
+  gdb_assert (action == FULL_RELOAD || action == UPDATE_OR_RELOAD);
+
+  /* Check that an appropriate number of arguments has been supplied.
+     We expect:
+       arg0: Lmid_t lmid (mandatory)
+       arg1: struct r_debug *debug_base (mandatory)
+       arg2: struct link_map *new (optional, for incremental updates)  */
+  probe_argc = get_probe_argument_count (pa->probe);
+  if (probe_argc == 2)
+    action = FULL_RELOAD;
+  else if (probe_argc < 2)
+    action = PROBES_INTERFACE_FAILED;
+
+  return action;
+}
+
+/* Populate the shared object list by reading the entire list of
+   shared objects from the inferior.  Returns nonzero on success.  */
+
+static int
+solist_update_full (struct svr4_info *info)
+{
+  free_solib_list (info);
+  info->solib_list = svr4_current_sos_direct (info);
+
+  return 1;
+}
+
+/* Update the shared object list starting from the link-map entry
+   passed by the linker in the probe's third argument.  Returns
+   nonzero if the list was successfully updated, or zero to indicate
+   failure.  */
+
+static int
+solist_update_incremental (struct svr4_info *info, CORE_ADDR lm)
+{
+  struct so_list *tail;
+  CORE_ADDR prev_lm;
+
+  /* Fall back to a full update if we haven't read anything yet.  */
+  if (info->solib_list == NULL)
+    return 0;
+
+  /* Fall back to a full update if we are using a remote target
+     that does not support incremental transfers.  */
+  if (info->using_xfer && !target_augmented_libraries_svr4_read())
+    return 0;
+
+  /* Walk to the end of the list.  */
+  for (tail = info->solib_list; tail->next; tail = tail->next)
+    /* Nothing.  */;
+  prev_lm = tail->lm_info->lm_addr;
+
+  /* Read the new objects.  */
+  if (info->using_xfer)
+    {
+      struct svr4_library_list library_list;
+      char annex[64];
+
+      xsnprintf (annex, sizeof (annex), "start=%s;prev=%s",
+		 phex_nz (lm, sizeof (lm)),
+		 phex_nz (prev_lm, sizeof (prev_lm)));
+      if (!svr4_current_sos_via_xfer_libraries (&library_list, annex))
+	return 0;
+
+      tail->next = library_list.head;
+    }
+  else
+    {
+      struct so_list **link = &tail->next;
+
+      if (!svr4_read_so_list (lm, prev_lm, &link, 0))
+	return 0;
+    }
+
+  return 1;
+}
+
+/* Disable the probes-based linker interface and revert to the
+   original interface.  We don't reset the breakpoints as the
+   ones set up for the probes-based interface are adequate.  */
+
+static void
+disable_probes_interface_cleanup (void *arg)
+{
+  struct svr4_info *info = get_svr4_info ();
+
+  warning (_("Probes-based dynamic linker interface failed.\n"
+	     "Reverting to original interface.\n"));
+
+  free_probes_table (info);
+  free_solib_list (info);
+}
+
+/* Update the solib list as appropriate when using the
+   probes-based linker interface.  Do nothing if using the
+   standard interface.  */
+
+static void
+svr4_handle_solib_event (void)
+{
+  struct svr4_info *info = get_svr4_info ();
+  struct probe_and_action *pa;
+  enum probe_action action;
+  struct cleanup *old_chain, *usm_chain;
+  struct value *val;
+  CORE_ADDR pc, debug_base, lm = 0;
+  int is_initial_ns;
+
+  /* Do nothing if not using the probes interface.  */
+  if (info->probes_table == NULL)
+    return;
+
+  /* If anything goes wrong we revert to the original linker
+     interface.  */
+  old_chain = make_cleanup (disable_probes_interface_cleanup, NULL);
+
+  pc = regcache_read_pc (get_current_regcache ());
+  pa = solib_event_probe_at (info, pc);
+  if (pa == NULL)
+    {
+      do_cleanups (old_chain);
+      return;
+    }
+
+  action = solib_event_probe_action (pa);
+  if (action == PROBES_INTERFACE_FAILED)
+    {
+      do_cleanups (old_chain);
+      return;
+    }
+
+  if (action == DO_NOTHING)
+    {
+      discard_cleanups (old_chain);
+      return;
+    }
+
+  /* evaluate_probe_argument looks up symbols in the dynamic linker
+     using find_pc_section.  find_pc_section is accelerated by a cache
+     called the section map.  The section map is invalidated every
+     time a shared library is loaded or unloaded, and if the inferior
+     is generating a lot of shared library events then the section map
+     will be updated every time svr4_handle_solib_event is called.
+     We called find_pc_section in svr4_create_solib_event_breakpoints,
+     so we can guarantee that the dynamic linker's sections are in the
+     section map.  We can therefore inhibit section map updates across
+     these calls to evaluate_probe_argument and save a lot of time.  */
+  inhibit_section_map_updates (current_program_space);
+  usm_chain = make_cleanup (resume_section_map_updates_cleanup,
+			    current_program_space);
+
+  val = evaluate_probe_argument (pa->probe, 1);
+  if (val == NULL)
+    {
+      do_cleanups (old_chain);
+      return;
+    }
+
+  debug_base = value_as_address (val);
+  if (debug_base == 0)
+    {
+      do_cleanups (old_chain);
+      return;
+    }
+
+  /* Always locate the debug struct, in case it moved.  */
+  info->debug_base = 0;
+  if (locate_base (info) == 0)
+    {
+      do_cleanups (old_chain);
+      return;
+    }
+
+  /* GDB does not currently support libraries loaded via dlmopen
+     into namespaces other than the initial one.  We must ignore
+     any namespace other than the initial namespace here until
+     support for this is added to GDB.  */
+  if (debug_base != info->debug_base)
+    action = DO_NOTHING;
+
+  if (action == UPDATE_OR_RELOAD)
+    {
+      val = evaluate_probe_argument (pa->probe, 2);
+      if (val != NULL)
+	lm = value_as_address (val);
+
+      if (lm == 0)
+	action = FULL_RELOAD;
+    }
+
+  /* Resume section map updates.  */
+  do_cleanups (usm_chain);
+
+  if (action == UPDATE_OR_RELOAD)
+    {
+      if (!solist_update_incremental (info, lm))
+	action = FULL_RELOAD;
+    }
+
+  if (action == FULL_RELOAD)
+    {
+      if (!solist_update_full (info))
+	{
+	  do_cleanups (old_chain);
+	  return;
+	}
+    }
+
+  discard_cleanups (old_chain);
+}
+
+/* Helper function for svr4_update_solib_event_breakpoints.  */
+
+static int
+svr4_update_solib_event_breakpoint (struct breakpoint *b, void *arg)
+{
+  struct svr4_info *info = get_svr4_info ();
+  struct bp_location *loc;
+
+  if (b->type != bp_shlib_event)
+    {
+      /* Continue iterating.  */
+      return 0;
+    }
+
+  for (loc = b->loc; loc; loc = loc->next)
+    {
+      struct probe_and_action *pa = solib_event_probe_at (info, loc->address);
+
+      if (pa != NULL)
+	{
+	  if (pa->action == DO_NOTHING)
+	    {
+	      if (b->enable_state == bp_disabled && stop_on_solib_events)
+		enable_breakpoint (b);
+	      else if (b->enable_state == bp_enabled && !stop_on_solib_events)
+		disable_breakpoint (b);
+	    }
+
+	  /* Continue iterating.  */
+	  return 0;
+	}
+    }
+
+  /* Continue iterating.  */
+  return 0;
+}
+
+/* Enable or disable optional solib event breakpoints as appropriate.
+   Called whenever stop_on_solib_events is changed.  */
+
+static void
+svr4_update_solib_event_breakpoints (void)
+{
+  struct svr4_info *info = get_svr4_info ();
+
+  if (info->probes_table != NULL)
+    iterate_over_breakpoints (svr4_update_solib_event_breakpoint, NULL);
+}
+
+/* Create and register solib event breakpoints.  PROBES is an array
+   of NUM_PROBES elements, each of which is vector of probes.  A
+   solib event breakpoint will be created and registered for each
+   probe.  */
+
+static void
+svr4_create_probe_breakpoints (struct gdbarch *gdbarch,
+			       VEC (probe_p) **probes)
+{
+  int i;
+
+  for (i = 0; i < NUM_PROBES; i++)
+    {
+      enum probe_action action = probe_info[i].action;
+      struct probe *probe;
+      int ix;
+
+      for (ix = 0;
+	   VEC_iterate (probe_p, probes[i], ix, probe);
+	   ++ix)
+	{
+	  create_solib_event_breakpoint (gdbarch, probe->address);
+	  register_solib_event_probe (probe, action);
+	}
+    }
+
+  svr4_update_solib_event_breakpoints ();
+}
+
+/* Both the SunOS and the SVR4 dynamic linkers call a marker function
+   before and after mapping and unmapping shared libraries.  The sole
+   purpose of this method is to allow debuggers to set a breakpoint so
+   they can track these changes.
+
+   Some versions of the glibc dynamic linker contain named probes
+   to allow more fine grained stopping.  Given the address of the
+   original marker function, this function attempts to find these
+   probes, and if found, sets breakpoints on those instead.  If the
+   probes aren't found, a single breakpoint is set on the original
+   marker function.  */
+
+static void
+svr4_create_solib_event_breakpoints (struct gdbarch *gdbarch,
+				     CORE_ADDR address)
+{
+  struct obj_section *os;
+
+  os = find_pc_section (address);
+  if (os != NULL)
+    {
+      int with_prefix;
+
+      for (with_prefix = 0; with_prefix <= 1; with_prefix++)
+	{
+	  VEC (probe_p) *probes[NUM_PROBES];
+	  int all_probes_found = 1;
+	  int i;
+
+	  memset (probes, 0, sizeof (probes));
+	  for (i = 0; i < NUM_PROBES; i++)
+	    {
+	      char name[32] = { '\0' };
+
+	      /* Fedora 17 and Red Hat Enterprise Linux 6.2-6.4
+		 shipped with an early version of the probes code in
+		 which the probes' names were prefixed with "rtld_"
+		 and the "map_failed" probe did not exist.  The
+		 locations of the probes are otherwise the same, so
+		 we check for probes with prefixed names if probes
+		 with unprefixed names are not present.  */
+
+	      if (with_prefix)
+		strncat (name, "rtld_", sizeof (name) - strlen (name) - 1);
+
+	      strncat (name, probe_info[i].name,
+		       sizeof (name) - strlen (name) - 1);
+
+	      probes[i] = find_probes_in_objfile (os->objfile, "rtld", name);
+
+	      /* The "map_failed" probe did not exist in early
+		 versions of the probes code in which the probes'
+		 names were prefixed with "rtld_".  */
+	      if (!strcmp (name,"rtld_map_failed"))
+		continue;
+
+	      if (VEC_empty (probe_p, probes[i]))
+		{
+		  all_probes_found = 0;
+		  break;
+		}
+	    }
+
+	  if (all_probes_found)
+	    svr4_create_probe_breakpoints (gdbarch, probes);
+
+	  for (i = 0; i < NUM_PROBES; i++)
+	    VEC_free (probe_p, probes[i]);
+
+	  if (all_probes_found)
+	    return;
+	}
+    }
+
+  create_solib_event_breakpoint (gdbarch, address);
+}
+
 /* Helper function for gdb_bfd_lookup_symbol.  */
 
 static int
@@ -1461,6 +2073,8 @@ enable_break (struct svr4_info *info, int from_tty)
   info->interp_text_sect_low = info->interp_text_sect_high = 0;
   info->interp_plt_sect_low = info->interp_plt_sect_high = 0;
 
+  free_probes_table (info);
+
   /* If we already have a shared library list in the target, and
      r_debug contains r_brk, set the breakpoint there - this should
      mean r_brk has already been relocated.  Assume the dynamic linker
@@ -1492,7 +2106,7 @@ enable_break (struct svr4_info *info, int from_tty)
 	 That knowledge is encoded in the address, if it's Thumb the low bit
 	 is 1.  However, we've stripped that info above and it's not clear
 	 what all the consequences are of passing a non-addr_bits_remove'd
-	 address to create_solib_event_breakpoint.  The call to
+	 address to svr4_create_solib_event_breakpoints.  The call to
 	 find_pc_section verifies we know about the address and have some
 	 hope of computing the right kind of breakpoint to use (via
 	 symbol info).  It does mean that GDB needs to be pointed at a
@@ -1530,7 +2144,7 @@ enable_break (struct svr4_info *info, int from_tty)
 		+ bfd_section_size (tmp_bfd, interp_sect);
 	    }
 
-	  create_solib_event_breakpoint (target_gdbarch (), sym_addr);
+	  svr4_create_solib_event_breakpoints (target_gdbarch (), sym_addr);
 	  return 1;
 	}
     }
@@ -1688,7 +2302,8 @@ enable_break (struct svr4_info *info, int from_tty)
 
       if (sym_addr != 0)
 	{
-	  create_solib_event_breakpoint (target_gdbarch (), load_addr + sym_addr);
+	  svr4_create_solib_event_breakpoints (target_gdbarch (),
+					       load_addr + sym_addr);
 	  xfree (interp_name);
 	  return 1;
 	}
@@ -1714,7 +2329,7 @@ enable_break (struct svr4_info *info, int from_tty)
 	  sym_addr = gdbarch_convert_from_func_ptr_addr (target_gdbarch (),
 							 sym_addr,
 							 &current_target);
-	  create_solib_event_breakpoint (target_gdbarch (), sym_addr);
+	  svr4_create_solib_event_breakpoints (target_gdbarch (), sym_addr);
 	  return 1;
 	}
     }
@@ -1730,7 +2345,7 @@ enable_break (struct svr4_info *info, int from_tty)
 	      sym_addr = gdbarch_convert_from_func_ptr_addr (target_gdbarch (),
 							     sym_addr,
 							     &current_target);
-	      create_solib_event_breakpoint (target_gdbarch (), sym_addr);
+	      svr4_create_solib_event_breakpoints (target_gdbarch (), sym_addr);
 	      return 1;
 	    }
 	}
@@ -2226,6 +2841,9 @@ svr4_solib_create_inferior_hook (int from_tty)
 
   info = get_svr4_info ();
 
+  /* Free the probes-based interface's solib list.  */
+  free_solib_list (info);
+
   /* Relocate the main executable if necessary.  */
   svr4_relocate_main_executable ();
 
@@ -2468,4 +3086,6 @@ _initialize_svr4_solib (void)
   svr4_so_ops.lookup_lib_global_symbol = elf_lookup_lib_symbol;
   svr4_so_ops.same = svr4_same;
   svr4_so_ops.keep_data_in_core = svr4_keep_data_in_core;
+  svr4_so_ops.update_breakpoints = svr4_update_solib_event_breakpoints;
+  svr4_so_ops.handle_event = svr4_handle_solib_event;
 }