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

[H.J. Lu]

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.

-- 
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]$