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

Message ID CAMe9rOqyFr_dUHCNccrYDPP8_Xq=4=TfLe-24_nLxigUQy0K1A@mail.gmail.com
State New
Headers show

Commit Message

H.J. Lu Feb. 4, 2015, 11:10 p.m. UTC 
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
>

Try this.
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Patch

diff --git a/gcc/varasm.c b/gcc/varasm.c
index eb65b1f..c95eebd 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -6826,7 +6826,15 @@  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))
+      /* If not building shared library, common or initialized symbols
+	 are also resolved locally, regardless they are weak or not.  */
+      if ((!shlib
+	   && (DECL_COMMON (exp)
+	       || (DECL_INITIAL (exp) != NULL
+		   && (in_lto_p
+		       || DECL_INITIAL (exp) != error_mark_node))))
+	  || (vnode && (resolution_local_p (vnode->resolution)
+			|| vnode->in_other_partition)))
 	resolved_locally = true;
       if (vnode
 	  && resolution_to_local_definition_p (vnode->resolution))