add short-circuit logic to elfread.c

If minimal symbols have already been read into a per-BFD object, then
a symbol reader can skip re-reading them.  This changes the ELF reader
to do so.

We only skip the work if the file is ELF+DWARF.  If it has stabs or
mdebug sections, then I think extra information is computed during the
minsym creation pass; and so we must still repeat it.  Eventually even
this will go away, once all symbol types have switched to being
progspace-independent.  In the meantime this has no negative effect --
it is just a missing optimization for a small set of users.

This change also required a somewhat non-obvious change to the OBJSTAT
accounting code.  If a symbol reader skips re-reading minimal symbols,
then the corresponding OBJSTAT will not be updated.  This leads to a
test failure in gdb.base/maint.exp.

To fix this, I've moved the needed stat field out of objfile and into
the per-BFD object.

2014-02-26  Tom Tromey  <tromey@redhat.com>

	* elfread.c (elf_read_minimal_symbols): Return early if
	minimal symbols have already been read.  Add "ei" parameter.
	(elf_symfile_read): Call elf_read_minimal_symbols earlier.
	* minsyms.c (prim_record_minimal_symbol_full): Update.
	* objfiles.h (struct objstats) <n_minsyms>: Move...
	(struct objfile_per_bfd_storage) <n_minsyms>: ... here.
	* symmisc.c (print_objfile_statistics): Update.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2014-02-26  Tom Tromey  <tromey@redhat.com>
+
+	* elfread.c (elf_read_minimal_symbols): Return early if
+	minimal symbols have already been read.  Add "ei" parameter.
+	(elf_symfile_read): Call elf_read_minimal_symbols earlier.
+	* minsyms.c (prim_record_minimal_symbol_full): Update.
+	* objfiles.h (struct objstats) <n_minsyms>: Move...
+	(struct objfile_per_bfd_storage) <n_minsyms>: ... here.
+	* symmisc.c (print_objfile_statistics): Update.
+
 2014-02-26  Tom Tromey  <tromey@redhat.com>
 
 	* elfread.c (elf_read_minimal_symbols): New function, from

gdb/elfread.c

@@ -1084,7 +1084,8 @@ elf_gnu_ifunc_resolver_return_stop (struct breakpoint *b)
    symbols.  */
 
 static void
-elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags)
+elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags,
+			  const struct elfinfo *ei)
 {
   bfd *synth_abfd, *abfd = objfile->obfd;
   struct cleanup *back_to;
@@ -1100,6 +1101,21 @@ elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags)
 			  objfile_name (objfile));
     }
 
+  /* If we already have minsyms, then we can skip some work here.
+     However, if there were stabs or mdebug sections, we go ahead and
+     redo all the work anyway, because the psym readers for those
+     kinds of debuginfo need extra information found here.  This can
+     go away once all types of symbols are in the per-BFD object.  */
+  if (objfile->per_bfd->minsyms_read
+      && ei->stabsect == NULL
+      && ei->mdebugsect == NULL)
+    {
+      if (symtab_create_debug)
+	fprintf_unfiltered (gdb_stdlog,
+			    "... minimal symbols previously read\n");
+      return;
+    }
+
   init_minimal_symbol_collection ();
   back_to = make_cleanup_discard_minimal_symbols ();
 
@@ -1242,16 +1258,11 @@ elf_symfile_read (struct objfile *objfile, int symfile_flags)
   bfd *abfd = objfile->obfd;
   struct elfinfo ei;
 
-  elf_read_minimal_symbols (objfile, symfile_flags);
-
   memset ((char *) &ei, 0, sizeof (ei));
-
-  /* Now process debugging information, which is contained in
-     special ELF sections.  */
-
-  /* We first have to find them...  */
   bfd_map_over_sections (abfd, elf_locate_sections, (void *) & ei);
 
+  elf_read_minimal_symbols (objfile, symfile_flags, &ei);
+
   /* ELF debugging information is inserted into the psymtab in the
      order of least informative first - most informative last.  Since
      the psymtab table is searched `most recent insertion first' this

gdb/minsyms.c

@@ -977,9 +977,11 @@ prim_record_minimal_symbol_full (const char *name, int name_len, int copy_name,
   /* If we already read minimal symbols for this objfile, then don't
      ever allocate a new one.  */
   if (!objfile->per_bfd->minsyms_read)
-    msym_bunch_index++;
+    {
+      msym_bunch_index++;
+      objfile->per_bfd->n_minsyms++;
+    }
   msym_count++;
-  OBJSTAT (objfile, n_minsyms++);
   return msymbol;
 }
 

gdb/objfiles.h

@@ -151,7 +151,6 @@ struct obj_section
 
 struct objstats
   {
-    int n_minsyms;		/* Number of minimal symbols read */
     int n_psyms;		/* Number of partial symbols read */
     int n_syms;			/* Number of full symbols read */
     int n_stabs;		/* Number of ".stabs" read (if applicable) */
@@ -224,6 +223,12 @@ struct objfile_per_bfd_storage
   struct minimal_symbol *msymbols;
   int minimal_symbol_count;
 
+  /* The number of minimal symbols read, before any minimal symbol
+     de-duplication is applied.  Note in particular that this has only
+     a passing relationship with the actual size of the table above;
+     use minimal_symbol_count if you need the true size.  */
+  int n_minsyms;
+
   /* This is true if minimal symbols have already been read.  Symbol
      readers can use this to bypass minimal symbol reading.  Also, the
      minimal symbol table management code in minsyms.c uses this to

gdb/symmisc.c

@@ -111,9 +111,9 @@ print_objfile_statistics (void)
     if (OBJSTAT (objfile, n_stabs) > 0)
       printf_filtered (_("  Number of \"stab\" symbols read: %d\n"),
 		       OBJSTAT (objfile, n_stabs));
-    if (OBJSTAT (objfile, n_minsyms) > 0)
+    if (objfile->per_bfd->n_minsyms > 0)
       printf_filtered (_("  Number of \"minimal\" symbols read: %d\n"),
-		       OBJSTAT (objfile, n_minsyms));
+		       objfile->per_bfd->n_minsyms);
     if (OBJSTAT (objfile, n_psyms) > 0)
       printf_filtered (_("  Number of \"partial\" symbols read: %d\n"),
 		       OBJSTAT (objfile, n_psyms));