use language of the main symbol

With "dwz -m", "main" appears in both the PU and the importing CU when
running anon-struct.exp.  However, the PU does not have a file name.
So, find_main_filename returns the empty string, making
deduce_language_from_filename return language_unknown.

This patch fixes this problem by changing gdb to use the ordinary
symbol-lookup functions to find "main"'s symbol.  Then, it examines the
symbol's language.

I think this is cleaner than the current approach.  For one thing it
avoids trying to guess the language based on the source file name,
instead deferring to the presumably more reliable debuginfo.

Another possible fix would have been to change how the file name is
found via the "qf" methods.  However, I think the approach given is
preferable for the reason outlined above.

This required a minor test suite change, as now a symtab is expanded
during the search for "main".

Built and regtested (both ways) on x86-64 Fedora 18.

	* symfile.c (set_initial_language): Look up "main" symbol
	and use its language.
	* symtab.c (find_main_filename): Remove.
	* symtab.h (find_main_filename): Remove.

	* gdb.base/maint.exp: Allow zero symtabs to be expanded.

6 files changed, 19 insertions, 32 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1097608..42e60aa 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2013-08-07  Tom Tromey  <tromey@redhat.com>
 
+	* symfile.c (set_initial_language): Look up "main" symbol
+	and use its language.
+	* symtab.c (find_main_filename): Remove.
+	* symtab.h (find_main_filename): Remove.
+
+2013-08-07  Tom Tromey  <tromey@redhat.com>
+
 	* dwarf2read.c (recursively_compute_inclusions): Add
 	"immediate_parent" argument.  Set symtab's "user" field
 	if not set.
diff --git a/gdb/symfile.c b/gdb/symfile.c
index 3328648..3dd5509 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1612,11 +1612,11 @@ set_initial_language (void)
     lang = language_of_main;
   else
     {
-      const char *filename;
+      char *name = main_name ();
+      struct symbol *sym = lookup_symbol (name, NULL, VAR_DOMAIN, NULL);
 
-      filename = find_main_filename ();
-      if (filename != NULL)
-	lang = deduce_language_from_filename (filename);
+      if (sym != NULL)
+	lang = SYMBOL_LANGUAGE (sym);
     }
 
   if (lang == language_unknown)
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 8076fe5..3bcec23 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -1949,29 +1949,6 @@ basic_lookup_transparent_type (const char *name)
   return (struct type *) 0;
 }
 
-/* Find the name of the file containing main().  */
-/* FIXME:  What about languages without main() or specially linked
-   executables that have no main() ?   */
-
-const char *
-find_main_filename (void)
-{
-  struct objfile *objfile;
-  char *name = main_name ();
-
-  ALL_OBJFILES (objfile)
-  {
-    const char *result;
-
-    if (!objfile->sf)
-      continue;
-    result = objfile->sf->qf->find_symbol_file (objfile, name);
-    if (result)
-      return result;
-  }
-  return (NULL);
-}
-
 /* Search BLOCK for symbol NAME in DOMAIN.
 
    Note that if NAME is the demangled form of a C++ symbol, we will fail
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 6d81507..ccf4a4f 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1252,8 +1252,6 @@ extern VEC (char_ptr) *make_source_files_completion_list (const char *,
 
 int matching_obj_sections (struct obj_section *, struct obj_section *);
 
-extern const char *find_main_filename (void);
-
 extern struct symtab *find_line_symtab (struct symtab *, int, int *, int *);
 
 extern struct symtab_and_line find_function_start_sal (struct symbol *sym,
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 160a27a..fb21761 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2013-08-07  Tom Tromey  <tromey@redhat.com>
 
+	* gdb.base/maint.exp: Allow zero symtabs to be expanded.
+
+2013-08-07  Tom Tromey  <tromey@redhat.com>
+
 	* gdb.dwarf2/dwz.exp: New file.
 
 2013-08-02  Tom Tromey  <tromey@redhat.com>
diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp
index 7057ac7..3093aae 100644
--- a/gdb/testsuite/gdb.base/maint.exp
+++ b/gdb/testsuite/gdb.base/maint.exp
@@ -72,9 +72,10 @@ gdb_test "maint print registers" "Name.*Nr.*Rel.*Offset.*Size.*Type.*"
 gdb_test_no_output "mt set per on" "mt set per on for expand-symtabs"
 gdb_test_multiple "mt expand-symtabs $subdir/break\[.\]c$" \
     "mt expand-symtabs" {
-	-re "#primary symtabs: (1|2) \\(\[+\](1|2)\\),.*$gdb_prompt $" {
-	    # This should expand one or at most two primary symtabs.
-	    # "Normally" it will expand just the one for break.c, but if the
+	-re "#primary symtabs: (1|2) \\(\[+\](0|1|2)\\),.*$gdb_prompt $" {
+	    # This should expand at most two primary symtabs.
+	    # "Normally" it will not expand any, because the symtab
+	    # holding "main" will already have been expanded, but if the
 	    # file is compiled with -fdebug-types-section then a second primary
 	    # symtab for break.c will be created for any types.
 	    pass "mt expand-symtabs"