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Re: [PATCH x86_64] Optimize access to globals in "-fpie -pie" builds with copy relocations
- From: Bernhard Reutner-Fischer <rep dot dot dot nop at gmail dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>,Sriraman Tallam <tmsriram at google dot com>
- Cc: Jakub Jelinek <jakub at redhat dot com>,Uros Bizjak <ubizjak at gmail dot com>,"gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>,David Li <davidxl at google dot com>,Cary Coutant <ccoutant at google dot com>
- Date: Wed, 04 Feb 2015 23:47:01 +0100
- Subject: Re: [PATCH x86_64] Optimize access to globals in "-fpie -pie" builds with copy relocations
- Authentication-results: sourceware.org; auth=none
- References: <20150203193615 dot GZ1746 at tucnak dot redhat dot com> <CAMe9rOrLwHdtsH2z_7dBpVKiJRtfT7iHaHO7wQ23o25TL7cTMw at mail dot gmail dot com> <CAAs8Hmw=Z9VeLz+MAY0X-POfkwXLFEsRFy8wEPDdyzVPV8ee=g at mail dot gmail dot com> <CAMe9rOouVu9Ndgf231iOt=ry0jWiw573H+y1KxycWkqSw=unOA at mail dot gmail dot com> <20150203221935 dot GA1746 at tucnak dot redhat dot com> <CAMe9rOq-A3YebgJ_xRnQDekYuvRw6C9GD9DYbhUizvr3OPad_Q at mail dot gmail dot com> <CAAs8Hmxdx1n+hgJ0oTAufPauz=S67oM2F_NAmyTzzUSh-ic=4Q at mail dot gmail dot com> <20150204183127 dot GU1746 at tucnak dot redhat dot com> <CAMe9rOpWUnex45v3hM9=tDNfnC6ipJ-hMEkiY1714Km15bL=bg at mail dot gmail dot com> <20150204184205 dot GW1746 at tucnak dot redhat dot com> <CAMe9rOoWkw==PQZt1hR1xjKaVxwkFh39vNbFb1WFbaxgxofJMA at mail dot gmail dot com> <CAAs8HmzByYULg8y0F2DnVo0YBnh__Jx2xSrvAoMYuWPJJb2q6A at mail dot gmail dot com> <CAMe9rOpFiaRuauCqFwUxYPEo46jPiQf8=W9+7Cf8q=1QCm0sEA at mail dot gmail dot com> <CAAs8HmwHY-vNEBdULByHYU__xKcKOarMqr-+69VRxo_kBkzwxw at mail dot gmail dot com> <CAMe9rOoGdDBpn12LFyTqdbfhdOxXgw4i9Xmk34fj=K+KzhSoAw at mail dot gmail dot com>
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
Thanks