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

[Sriraman Tallam <tmsriram at google dot com>]

On Thu, Feb 5, 2015 at 2:23 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Feb 5, 2015 at 2:05 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> On Thu, Feb 5, 2015 at 11:59 AM, Richard Henderson <rth@redhat.com> wrote:
>>> On 02/05/2015 11:01 AM, H.J. Lu wrote:
>>>> Can you elaborate why it depends on COPY relocation?  There
>>>> is no COPY relocation on x86-64.
>>>
>>> Ho hum, we appear to have switched topics mid-thread.
>>>
>>> I agree that we cannot override a weak symbol in the executable with even a
>>> non-weak symbol in a shared library.
>>
>> Hi HJ,
>>
>>    Is your patch supposed to fix weak symbols too?  Will
>> SYMBOL_REF_LOCAL_P evaluate to true for weak defined symbols with this
>> patch?  I tested this in gcc-4_9 and it didnt seem to do that.
>
> I am working on a comprehensive patch.  I will post it
> after testing is finished.


Thanks!

Sri

>
> --
> H.J.
> --
> [hjl@gnu-6 copyreloc-3]$  cat initweak.i
> __attribute__((weak))
> int xxxxxxxxxxxx = -1;
>
> int
> foo ()
> {
>   return xxxxxxxxxxxx;
> }
> [hjl@gnu-6 copyreloc-3]$ cat commonweak.i
> __attribute__((weak))
> int xxxxxxxxxxxx;
>
> int
> foo ()
> {
>   return xxxxxxxxxxxx;
> }
> [hjl@gnu-6 copyreloc-3]$ make initweak.s commonweak.s
> /export/build/gnu/gcc-x32/build-x86_64-linux/gcc/xgcc
> -B/export/build/gnu/gcc-x32/build-x86_64-linux/gcc/ -pie -fpie -O3
> -fuse-ld=gold -S initweak.i
> /export/build/gnu/gcc-x32/build-x86_64-linux/gcc/xgcc
> -B/export/build/gnu/gcc-x32/build-x86_64-linux/gcc/ -pie -fpie -O3
> -fuse-ld=gold -S commonweak.i
> [hjl@gnu-6 copyreloc-3]$ cat commonweak.s initweak.s
> .file "commonweak.i"
> .section .text.unlikely,"ax",@progbits
> .LCOLDB0:
> .text
> .LHOTB0:
> .p2align 4,,15
> .globl foo
> .type foo, @function
> foo:
> .LFB0:
> .cfi_startproc
> movl xxxxxxxxxxxx(%rip), %eax
> ret
> .cfi_endproc
> .LFE0:
> .size foo, .-foo
> .section .text.unlikely
> .LCOLDE0:
> .text
> .LHOTE0:
> .weak xxxxxxxxxxxx
> .bss
> .align 4
> .type xxxxxxxxxxxx, @object
> .size xxxxxxxxxxxx, 4
> xxxxxxxxxxxx:
> .zero 4
> .ident "GCC: (GNU) 5.0.0 20150205 (experimental)"
> .section .note.GNU-stack,"",@progbits
> .file "initweak.i"
> .section .text.unlikely,"ax",@progbits
> .LCOLDB0:
> .text
> .LHOTB0:
> .p2align 4,,15
> .globl foo
> .type foo, @function
> foo:
> .LFB0:
> .cfi_startproc
> movl xxxxxxxxxxxx(%rip), %eax
> ret
> .cfi_endproc
> .LFE0:
> .size foo, .-foo
> .section .text.unlikely
> .LCOLDE0:
> .text
> .LHOTE0:
> .weak xxxxxxxxxxxx
> .data
> .align 4
> .type xxxxxxxxxxxx, @object
> .size xxxxxxxxxxxx, 4
> xxxxxxxxxxxx:
> .long -1
> .ident "GCC: (GNU) 5.0.0 20150205 (experimental)"
> .section .note.GNU-stack,"",@progbits
> [hjl@gnu-6 copyreloc-3]$