Re: [patch] Speed up find_pc_section

[Paul Pluzhnikov <ppluzhnikov@google.com>]

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On Fri, Aug 7, 2009 at 3:29 PM, Paul Pluzhnikov<ppluzhnikov@google.com> wrote:

> I was able to reproduce the failed assert on F11/i586, but only after the
> system ran for a while.

Update: running 'make check' on F11 after prelinking shows many
similar failures. The "java setup" in Tom's repro instructions doesn't
appear necessary.

Here is a fix. Tested on F11/i586 (with prelinking) and Linux/x86_64 (without).

Thanks,
-- 
Paul Pluzhnikov

2009-08-08  Paul Pluzhnikov  <ppluzhnikov@google.com>

        * objfiles.c (qsort_cmp): Remove assert.
        (preferred_obj_section): New function.
        (update_section_map): Filter duplicates.

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Index: objfiles.c
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.c,v
retrieving revision 1.89
diff -p -u -r1.89 objfiles.c
--- objfiles.c	4 Aug 2009 18:46:05 -0000	1.89
+++ objfiles.c	8 Aug 2009 17:55:54 -0000
@@ -797,18 +797,36 @@ qsort_cmp (const void *a, const void *b)
       gdb_assert (sect1_addr >= obj_section_endaddr (sect2));
       return 1;
     }
-  /* This can happen for separate debug-info files.  */
-  gdb_assert (obj_section_endaddr (sect1) == obj_section_endaddr (sect2));
 
   return 0;
 }
 
+/* Select "better" obj_section to keep.  We prefer the one that came from
+   the real object, rather than the one from separate debuginfo.
+   Most of the time the two sections are exactly identical, but with
+   prelinking the .rel.dyn section in the real object may have different
+   size.  */
+
+static struct obj_section *
+preferred_obj_section (struct obj_section *a, struct obj_section *b)
+{
+  gdb_assert (obj_section_addr (a) == obj_section_addr (b));
+  gdb_assert ((a->objfile->separate_debug_objfile == b->objfile)
+	      || (b->objfile->separate_debug_objfile == a->objfile));
+  gdb_assert ((a->objfile->separate_debug_objfile_backlink == b->objfile)
+	      || (b->objfile->separate_debug_objfile_backlink == a->objfile));
+
+  if (a->objfile->separate_debug_objfile != NULL)
+    return a;
+  return b;
+}
+
 /* Update PMAP, PMAP_SIZE with non-TLS sections from all objfiles.  */
 
 static void
 update_section_map (struct obj_section ***pmap, int *pmap_size)
 {
-  int map_size, idx;
+  int map_size, i, j;
   struct obj_section *s, **map;
   struct objfile *objfile;
 
@@ -828,15 +846,45 @@ update_section_map (struct obj_section *
 
   map = xmalloc (map_size * sizeof (*map));
 
-  idx = 0;
+  i = 0;
   ALL_OBJSECTIONS (objfile, s)
     if (insert_p (objfile, s))
-      map[idx++] = s;
+      map[i++] = s;
 
 #undef insert_p
 
   qsort (map, map_size, sizeof (*map), qsort_cmp);
 
+  /* With separate debuginfo files, we may have up to two (almost)
+     identical copies of some obj_sections in the map.
+     Filter out duplicates.  */
+  for (i = 0, j = 0; i < map_size; ++i)
+    {
+      struct obj_section *sect1 = map[i];
+      struct obj_section *sect2 = (i + 1 < map_size) ? map[i + 1] : NULL;
+
+      if (sect2 == NULL
+	  || obj_section_addr (sect1) != obj_section_addr (sect2))
+	map[j++] = sect1;
+      else
+	{
+	  map[j++] = preferred_obj_section (sect1, sect2);
+	  ++i;
+	}
+    }
+
+  if (j < map_size)
+    {
+      /* Some duplicates were eliminated.
+	 The new size shouldn't be less than half of the original. */
+      gdb_assert (map_size / 2 <= j);
+      map_size = j;
+
+      map = xrealloc (map, map_size * sizeof (*map));  /* Trim excess space.  */
+    }
+  else
+    gdb_assert (j == map_size);
+
   *pmap = map;
   *pmap_size = map_size;
 }