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Subject: Re: [PATCH x86_64] Optimize access to globals in "-fpie -pie" builds with copy relocations
From: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Date: Wed, 03 Sep 2014 07:25:00 -0000
To: Richard Henderson <rth@redhat.com>,Sriraman Tallam <tmsriram@google.com>,GCC Patches <gcc-patches@gcc.gnu.org>,David Li <davidxl@google.com>,Cary Coutant <ccoutant@google.com>,Ian Lance Taylor <iant@google.com>,Paul Pluzhnikov <ppluzhnikov@google.com>
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On 2 September 2014 22:40:50 CEST, Richard Henderson <rth@redhat.com> wrote:
>On 06/20/2014 05:17 PM, Sriraman Tallam wrote:
>> Index: config/i386/i386.c
>> ===================================================================
>> --- config/i386/i386.c	(revision 211826)
>> +++ config/i386/i386.c	(working copy)
>> @@ -12691,7 +12691,9 @@ legitimate_pic_address_disp_p (rtx disp)
>>  		return true;
>>  	    }
>>  	  else if (!SYMBOL_REF_FAR_ADDR_P (op0)
>> -		   && SYMBOL_REF_LOCAL_P (op0)
>> +		   && (SYMBOL_REF_LOCAL_P (op0)
>> +		       || (TARGET_64BIT && ix86_copyrelocs && flag_pie
>> +			   && !SYMBOL_REF_FUNCTION_P (op0)))
>>  		   && ix86_cmodel != CM_LARGE_PIC)
>>  	    return true;
>>  	  break;
>
>This is the wrong place to patch.
>
>You ought to be adjusting SYMBOL_REF_LOCAL_P, by providing a modified
>TARGET_BINDS_LOCAL_P.
>
>Note in particular that I believe that you are doing the wrong thing
>with weak
>and COMMON symbols, in that you probably ought not force a copy reloc
>there.
>
>Note the complexity of default_binds_local_p_1, and the fact that all
>you
>really want to modify is
>
>  /* If PIC, then assume that any global name can be overridden by
>     symbols resolved from other modules.  */
>  else if (shlib)
>    local_p = false;
>
>near the bottom of that function.

Reminds me of PR32219 https://gcc.gnu.org/ml/gcc-patches/2010-03/msg00665.html
but admittedly that is not PIE imposed but still fails on current trunk..