Re: [RFA 5/4 take 2] Improved linker-debugger interface

[Gary Benson <gbenson@redhat.com>]

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Tom Tromey wrote:
> >>>>> "Gary" == Gary Benson <gbenson@redhat.com> writes:
> Gary> +/* See comments in objfiles.h.  */
> Gary> +
> Gary> +void
> Gary> +inhibit_section_map_updates (void)
> Gary> +{
> Gary> +  get_objfile_pspace_data (current_program_space)->inhibit_updates = 1;
> Gary> +
> Gary> +}
> 
> Spurious blank line before the "}".
> 
> Gary> @@ -1820,6 +1820,18 @@ svr4_handle_solib_event (bpstat bs)
> [...]
> Gary> +  inhibit_section_map_updates ();
> [...]
> Gary> +  resume_section_map_updates ();
> 
> If there is any possibility of throwing an exception between these
> calls, then there should be a cleanup instead.
[snip]
> If there is no possibility, then this patch is ok.

I think it is possible, so I've changed it.

Attached is an updated patch with both these fixes.

Thanks,
Gary

-- 
http://gbenson.net/

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2012-07-30  Gary Benson  <gbenson@redhat.com>

	* objfiles.h (inhibit_section_map_updates): New function
	declaration.
	(resume_section_map_updates): Likewise.
	(resume_section_map_updates_cleanup): Likewise.
	* objfiles.c (objfile_pspace_info): New field "inhibit_updates".
	(find_pc_section): Do not update the section map if
	inhibit_updates is set.
	(inhibit_section_map_updates): New function.
	(resume_section_map_updates): Likewise.
	(resume_section_map_updates_cleanup): Likewise.
	* solib-svr4.c (svr4_handle_solib_event): Inhibit section map
	updates for calls to evaluate_probe_argument.

diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index 0df5798..c7db1f2 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -522,6 +522,22 @@
 extern void *objfile_data (struct objfile *objfile,
 			   const struct objfile_data *data);
 
+/* In normal use, the section map will be rebuilt by FIND_PC_SECTION
+   if objfiles have been added, removed or relocated since it was last
+   called.  Calling INHIBIT_SECTION_MAP_UPDATES will inhibit this
+   behavior until RESUME_SECTION_MAP_UPDATES is called.  If you call
+   INHIBIT_SECTION_MAP_UPDATES you must ensure that every call to
+   FIND_PC_SECTION in the inhibited region relates to a section that
+   is already in the section map and has not since been removed or
+   relocated.  */
+extern void inhibit_section_map_updates (void);
+
+/* Resume automatically rebuilding the section map as required.  */
+extern void resume_section_map_updates (void);
+
+/* Version of the above suitable for use as a cleanup.  */
+extern void resume_section_map_updates_cleanup (void *arg);
+
 extern void default_iterate_over_objfiles_in_search_order
   (struct gdbarch *gdbarch,
    iterate_over_objfiles_in_search_order_cb_ftype *cb,
diff --git a/gdb/objfiles.c b/gdb/objfiles.c
index 5ff0eb2..327b5d6 100644
--- a/gdb/objfiles.c
+++ b/gdb/objfiles.c
@@ -70,6 +70,9 @@ struct objfile_pspace_info
   int objfiles_changed_p;
   struct obj_section **sections;
   int num_sections;
+
+  /* Nonzero if section map updates should be inhibited.  */
+  int inhibit_updates;
 };
 
 /* Per-program-space data key.  */
@@ -1289,7 +1292,7 @@ find_pc_section (CORE_ADDR pc)
     return s;
 
   pspace_info = get_objfile_pspace_data (current_program_space);
-  if (pspace_info->objfiles_changed_p != 0)
+  if (pspace_info->objfiles_changed_p && !pspace_info->inhibit_updates)
     {
       update_section_map (current_program_space,
 			  &pspace_info->sections,
@@ -1457,6 +1460,30 @@
   get_objfile_pspace_data (current_program_space)->objfiles_changed_p = 1;
 }
 
+/* See comments in objfiles.h.  */
+
+void
+inhibit_section_map_updates (void)
+{
+  get_objfile_pspace_data (current_program_space)->inhibit_updates = 1;
+}
+
+/* See comments in objfiles.h.  */
+
+void
+resume_section_map_updates (void)
+{
+  get_objfile_pspace_data (current_program_space)->inhibit_updates = 0;
+}
+
+/* See comments in objfiles.h.  */
+
+void
+resume_section_map_updates_cleanup (void *arg)
+{
+  resume_section_map_updates ();
+}
+
 /* The default implementation for the "iterate_over_objfiles_in_search_order"
    gdbarch method.  It is equivalent to use the ALL_OBJFILES macro,
    searching the objfiles in the order they are stored internally,
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 17395f7..d3c388b 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1796,6 +1796,7 @@
   struct svr4_info *info = get_svr4_info ();
   struct probe_and_info buf, *pi;
   enum probe_action action;
+  struct cleanup *cleanups = NULL;
   struct value *val;
   LONGEST lmid;
   CORE_ADDR debug_base, lm = 0;
@@ -1820,6 +1821,19 @@
   if (action == NAMESPACE_NO_ACTION)
     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 ();
+  cleanups = make_cleanup (resume_section_map_updates_cleanup, NULL);
+
   val = evaluate_probe_argument (pi->probe, 0);
   if (val == NULL)
     goto error;
@@ -1851,6 +1865,9 @@
 	action = NAMESPACE_RELOAD;
     }
 
+  do_cleanups (cleanups);
+  cleanups = NULL;
+
   if (action == NAMESPACE_UPDATE_OR_RELOAD)
     {
       if (namespace_update_incremental (info, lmid, lm, is_initial_ns))
@@ -1873,6 +1890,8 @@
   warning (_("Probes-based dynamic linker interface failed.\n"
 	     "Reverting to original interface.\n"));
 
+  if (cleanups != NULL)
+    do_cleanups (cleanups);
   free_namespace_table (info);
   free_probes (info);
   info->using_probes = 0;