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.

1 files changed, 19 insertions, 8 deletions

diff --git a/gdb/elfread.c b/gdb/elfread.c
index 3aec352..88fb018 100644
--- a/gdb/elfread.c
+++ b/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