[GOLD] Fix spurious "plugin needed to handle lto object" warnings

[Alan Modra]

lto_slim_object_ was unitialized.  I also thought it worth adding
a sanity check on the .gnu.lto_.lto.* section size, and made some
other tidies.

I'm applying this to the branch too.

	PR 24768
	* layout.cc (Layout::Layout): Init lto_slim_object_.
	* object.cc (Sized_relobj_file::do_layout): Wrap overlong line.
	Don't use C cast.  Validate section size.  Don't copy contents.

diff --git a/gold/layout.cc b/gold/layout.cc
index fc7cdf8b8b..194d088c2a 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -466,6 +466,7 @@ Layout::Layout(int number_of_input_files, Script_options* script_options)
     unique_segment_for_sections_specified_(false),
     incremental_inputs_(NULL),
     record_output_section_data_from_script_(false),
+    lto_slim_object_(false),
     script_output_section_data_list_(),
     segment_states_(NULL),
     relaxation_debug_check_(NULL),
diff --git a/gold/object.cc b/gold/object.cc
index d505ce4752..fd594ac56d 100644
--- a/gold/object.cc
+++ b/gold/object.cc
@@ -1884,10 +1884,15 @@ Sized_relobj_file<size, big_endian>::do_layout(Symbol_table* symtab,
       if (strncmp (name, lto_section_name, strlen (lto_section_name)) == 0)
 	{
 	  section_size_type contents_len;
-	  const unsigned char* pcontents = this->section_contents(i, &contents_len, false);
-	  struct lto_section lsection = *(const lto_section*)pcontents;
-	  if (lsection.slim_object)
-	    layout->set_lto_slim_object ();
+	  const unsigned char* pcontents
+	    = this->section_contents(i, &contents_len, false);
+	  if (contents_len >= sizeof(lto_section))
+	    {
+	      const lto_section* lsection
+		= reinterpret_cast<const lto_section*>(pcontents);
+	      if (lsection->slim_object)
+		layout->set_lto_slim_object();
+	    }
 	}
     }
 

-- 
Alan Modra
Australia Development Lab, IBM