Re: [RFC/RFA] Per-objfile data mechanism

[Mark Kettenis <kettenis@chello.nl>]

   From: David Carlton <carlton@kealia.com>
   Date: Tue, 12 Aug 2003 13:51:38 -0700

   > I just converted gdbarch to an obstack and encountered two occasions
   > where xmrealloc would have made my life a little easier.  Instead of
   > proposing the use of mmalloc (and hence xmrealloc) though, I modified
   > the algorithms / structures a little and avoided the problem.

   > Is it possible that the same situtation is being encountered here?  A
   > growable hash table can be implemented without needing to reclaim
   > memory - something more along the lines of a btree?

   Sure, I could replace the data structure in question by a different
   one which is more obstack-friendly; it would be work, and the
   resulting code would initially be less reliable, but it could be done.
   But I guess I don't understand why obstacks are supposed to be so
   wonderful.  They're useful if you're allocating zillions of small
   objects that should all disappear at the same time, but I don't see
   the value of trying to fit all of our data structures into them.

OK, this discussion is moving away from the origional question.  I
concluded that we want the per-objfile data, and that, we might want a
destructor mechanism.  I checked in my origional patch, since the
destructor mechanism can easily be added later.

It is my understanding that this patch fixes some real bugs, and that
we should consider adding this to 6.0.  Having it on mainline is a
first step.

Mark


Index: ChangeLog
from  Mark Kettenis  <kettenis@gnu.org>

	* objfiles.h (struct objfile): Add memebers `data' and `num_data'.
	(register_objfile_data, set_objfile_data, objfile_data): New
	prototypes.
	* objfiles.c (objfile_alloc_data, objfile_free_data): New
	prototypes.
	(allocate_objfile): Call objfile_alloc_data.
	(free_objfile): Call objfile_free_data.
	(struct objfile_data): New.
	(struct objfile_data_registration): New.
	(struct objfile_data_registry): New.
	(objfile_data_registry): New variable.
	(register_objfile_data): New function.
	(objfile_alloc_data, objfile_free_data): New functions.
	(set_objfile_data, objfile_data): New functions.
	* dwarf2-frame.c (dwarf2_frame_data): New variable.
	(dwarf2_frame_find_fde, add_fde): Use new per-objfile data mechanism.
	(_initialize_dwarf2_frame): New function and prototype.

Index: dwarf2-frame.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2-frame.c,v
retrieving revision 1.10
diff -u -p -r1.10 dwarf2-frame.c
--- dwarf2-frame.c 18 Jul 2003 19:59:27 -0000 1.10
+++ dwarf2-frame.c 21 Aug 2003 22:33:51 -0000
@@ -780,6 +780,8 @@ struct comp_unit
   bfd_vma dbase;
 };
 
+const struct objfile_data *dwarf2_frame_data;
+
 static unsigned int
 read_1_byte (bfd *bfd, char *buf)
 {
@@ -1024,7 +1026,7 @@ dwarf2_frame_find_fde (CORE_ADDR *pc)
 
       offset = ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
       
-      fde = objfile->sym_private;
+      fde = objfile_data (objfile, dwarf2_frame_data);
       while (fde)
 	{
 	  if (*pc >= fde->initial_location + offset
@@ -1044,8 +1046,8 @@ dwarf2_frame_find_fde (CORE_ADDR *pc)
 static void
 add_fde (struct comp_unit *unit, struct dwarf2_fde *fde)
 {
-  fde->next = unit->objfile->sym_private;
-  unit->objfile->sym_private = fde;
+  fde->next = objfile_data (unit->objfile, dwarf2_frame_data);
+  set_objfile_data (unit->objfile, dwarf2_frame_data, fde);
 }
 
 #ifdef CC_HAS_LONG_LONG
@@ -1440,4 +1442,13 @@ dwarf2_build_frame_info (struct objfile 
       while (frame_ptr < unit.dwarf_frame_buffer + unit.dwarf_frame_size)
 	frame_ptr = decode_frame_entry (&unit, frame_ptr, 0);
     }
+}
+
+/* Provide a prototype to silence -Wmissing-prototypes.  */
+void _initialize_dwarf2_frame (void);
+
+void
+_initialize_dwarf2_frame (void)
+{
+  dwarf2_frame_data = register_objfile_data ();
 }
Index: objfiles.c
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.c,v
retrieving revision 1.33
diff -u -p -r1.33 objfiles.c
--- objfiles.c 11 Jun 2003 23:29:47 -0000 1.33
+++ objfiles.c 21 Aug 2003 22:33:51 -0000
@@ -34,6 +34,7 @@
 #include "target.h"
 #include "bcache.h"
 
+#include "gdb_assert.h"
 #include <sys/types.h>
 #include "gdb_stat.h"
 #include <fcntl.h>
@@ -61,6 +62,9 @@ static void *map_to_file (int);
 
 static void add_to_objfile_sections (bfd *, sec_ptr, void *);
 
+static void objfile_alloc_data (struct objfile *objfile);
+static void objfile_free_data (struct objfile *objfile);
+
 /* Externally visible variables that are owned by this module.
    See declarations in objfile.h for more info. */
 
@@ -302,6 +306,8 @@ allocate_objfile (bfd *abfd, int flags)
       terminate_minimal_symbol_table (objfile);
     }
 
+  objfile_alloc_data (objfile);
+
   /* Update the per-objfile information that comes from the bfd, ensuring
      that any data that is reference is saved in the per-objfile data
      region. */
@@ -561,6 +567,7 @@ free_objfile (struct objfile *objfile)
 
   if (objfile != NULL)
     {
+      objfile_free_data (objfile);
       if (objfile->name != NULL)
 	{
 	  xmfree (objfile->md, objfile->name);
@@ -1097,4 +1104,74 @@ is_in_import_list (char *name, struct ob
       return 1;
   return 0;
 }
+\f
+
+/* Keep a registry of per-objfile data-pointers required by other GDB
+   modules.  */
+
+struct objfile_data
+{
+  unsigned index;
+};
+
+struct objfile_data_registration
+{
+  struct objfile_data *data;
+  struct objfile_data_registration *next;
+};
+  
+struct objfile_data_registry
+{
+  struct objfile_data_registration *registrations;
+  unsigned num_registrations;
+};
+
+static struct objfile_data_registry objfile_data_registry = { NULL, 0 };
+
+const struct objfile_data *
+register_objfile_data (void)
+{
+  struct objfile_data_registration **curr;
+
+  /* Append new registration.  */
+  for (curr = &objfile_data_registry.registrations;
+       *curr != NULL; curr = &(*curr)->next);
 
+  *curr = XMALLOC (struct objfile_data_registration);
+  (*curr)->next = NULL;
+  (*curr)->data = XMALLOC (struct objfile_data);
+  (*curr)->data->index = objfile_data_registry.num_registrations++;
+
+  return (*curr)->data;
+}
+
+static void
+objfile_alloc_data (struct objfile *objfile)
+{
+  gdb_assert (objfile->data == NULL);
+  objfile->num_data = objfile_data_registry.num_registrations;
+  objfile->data = XCALLOC (objfile->num_data, void *);
+}
+
+static void
+objfile_free_data (struct objfile *objfile)
+{
+  gdb_assert (objfile->data != NULL);
+  xfree (objfile->data);
+  objfile->data = NULL;
+}
+
+void
+set_objfile_data (struct objfile *objfile, const struct objfile_data *data,
+		  void *value)
+{
+  gdb_assert (data->index < objfile->num_data);
+  objfile->data[data->index] = value;
+}
+
+void *
+objfile_data (struct objfile *objfile, const struct objfile_data *data)
+{
+  gdb_assert (data->index < objfile->num_data);
+  return objfile->data[data->index];
+}
Index: objfiles.h
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.h,v
retrieving revision 1.22
diff -u -p -r1.22 objfiles.h
--- objfiles.h 24 Mar 2003 03:54:48 -0000 1.22
+++ objfiles.h 21 Aug 2003 22:33:52 -0000
@@ -379,6 +379,13 @@ struct objfile
 
     void *obj_private;
 
+    /* Per objfile data-pointers required by other GDB modules.  */
+    /* FIXME: kettenis/20030711: This mechanism could replace
+       sym_stab_info, sym_private and obj_private entirely.  */
+
+    void **data;
+    unsigned num_data;
+
     /* Set of relocation offsets to apply to each section.
        Currently on the psymbol_obstack (which makes no sense, but I'm
        not sure it's harming anything).
@@ -564,6 +571,16 @@ extern struct obj_section *find_pc_sect_
 extern int in_plt_section (CORE_ADDR, char *);
 
 extern int is_in_import_list (char *, struct objfile *);
+
+/* Keep a registry of per-objfile data-pointers required by other GDB
+   modules.  */
+
+extern const struct objfile_data *register_objfile_data (void);
+extern void set_objfile_data (struct objfile *objfile,
+			      const struct objfile_data *data, void *value);
+extern void *objfile_data (struct objfile *objfile,
+			   const struct objfile_data *data);
+\f
 
 /* Traverse all object files.  ALL_OBJFILES_SAFE works even if you delete
    the objfile during the traversal.  */