Re: [PATCH x86_64] Optimize access to globals in "-fpie -pie" builds with copy relocations

["H.J. Lu" <hjl.tools@gmail.com>]

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On Wed, Feb 4, 2015 at 3:10 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Feb 4, 2015 at 2:47 PM, Bernhard Reutner-Fischer
> <rep.dot.nop@gmail.com> wrote:
>> On February 4, 2015 11:37:01 PM GMT+01:00, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>>On Wed, Feb 4, 2015 at 1:53 PM, Sriraman Tallam <tmsriram@google.com>
>>>wrote:
>>>> On Wed, Feb 4, 2015 at 10:57 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>> On Wed, Feb 4, 2015 at 10:51 AM, Sriraman Tallam
>>><tmsriram@google.com> wrote:
>>>>>> On Wed, Feb 4, 2015 at 10:45 AM, H.J. Lu <hjl.tools@gmail.com>
>>>wrote:
>>>>>>> On Wed, Feb 4, 2015 at 10:42 AM, Jakub Jelinek <jakub@redhat.com>
>>>wrote:
>>>>>>>> On Wed, Feb 04, 2015 at 10:38:48AM -0800, H.J. Lu wrote:
>>>>>>>>> Common symbol should be resolved locally for PIE.
>>>>>>>>
>>>>>>>> binds_local_p yes, binds_to_current_def_p no.
>>>>>>>>
>>>>>>>
>>>>>>> Is SYMBOL_REF_LOCAL_P set to binds_local_p or
>>>>>>> binds_to_current_def_p?
>>>>>>
>>>>>> Looks like binds_local_p:
>>>>>>
>>>>>> varasm.c:
>>>>>> void
>>>>>> default_encode_section_info (tree decl, rtx rtl, int first
>>>ATTRIBUTE_UNUSED)
>>>>>> {
>>>>>>   ...
>>>>>>   if (targetm.binds_local_p (decl))
>>>>>>     flags |= SYMBOL_FLAG_LOCAL;
>>>>>>
>>>>>
>>>>> Why is SYMBOL_REF_LOCAL_P false?
>>>>
>>>> In varasm.c, default_binds_local_p_1
>>>>
>>>>
>>>>  /* Default visibility weak data can be overridden by a strong symbol
>>>>      in another module and so are not local.  */
>>>>   else if (DECL_WEAK (exp)
>>>>   && !resolved_locally)
>>>           ^^^^^^^^^^^^^^^^^^^
>>>Why is resolved_locally false? It should be true for common
>>>symbol when compiling for PIE.
>>>
>>>>     local_p = false;
>>>>
>>>> For weak definition, it is set to false here.
>>
>> Yea and i think this is still wrong and known as
>> http://gcc.gnu.org/PR32219
>>
>

I am testing this patch.



-- 
H.J.

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diff --git a/gcc/varasm.c b/gcc/varasm.c
index eb65b1f..36fd393 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -6826,11 +6826,17 @@ default_binds_local_p_1 (const_tree exp, int shlib)
       && (TREE_STATIC (exp) || DECL_EXTERNAL (exp)))
     {
       varpool_node *vnode = varpool_node::get (exp);
-      if (vnode && (resolution_local_p (vnode->resolution) || vnode->in_other_partition))
-	resolved_locally = true;
-      if (vnode
-	  && resolution_to_local_definition_p (vnode->resolution))
-	resolved_to_local_def = true;
+      /* If not building shared library, common or initialized symbols
+	 are also resolved locally, regardless they are weak or not.  */
+      if (vnode)
+	{
+	  if ((!shlib && vnode->definition)
+	      || vnode->in_other_partition
+	      || resolution_local_p (vnode->resolution))
+	    resolved_locally = true;
+	  if (resolution_to_local_definition_p (vnode->resolution))
+	    resolved_to_local_def = true;
+	}
     }
   else if (TREE_CODE (exp) == FUNCTION_DECL && TREE_PUBLIC (exp))
     {
@@ -6880,13 +6886,6 @@ default_binds_local_p_1 (const_tree exp, int shlib)
      symbols resolved from other modules.  */
   else if (shlib)
     local_p = false;
-  /* Uninitialized COMMON variable may be unified with symbols
-     resolved from other modules.  */
-  else if (DECL_COMMON (exp)
-	   && !resolved_locally
-	   && (DECL_INITIAL (exp) == NULL
-	       || (!in_lto_p && DECL_INITIAL (exp) == error_mark_node)))
-    local_p = false;
   /* Otherwise we're left with initialized (or non-common) global data
      which is of necessity defined locally.  */
   else