Re: [PATCH] MdePkg: move to 'hidden' visibility for all symbols under GCC/X64

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 2 August 2016 at 04:49, Gao, Liming <liming.gao@intel.com> wrote:
> Reviewed-by: Liming Gao <liming.gao@intel.com>
>

Thanks
Pushed as 28ade7b802e0

-- 
Ard.

>> -----Original Message-----
>> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>> Sent: Monday, August 01, 2016 2:57 PM
>> To: Shi, Steven <steven.shi@intel.com>; Zhu, Yonghong
>> <yonghong.zhu@intel.com>; Gao, Liming <liming.gao@intel.com>; Justen,
>> Jordan L <jordan.l.justen@intel.com>; edk2-devel@lists.01.org
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Subject: [PATCH] MdePkg: move to 'hidden' visibility for all symbols under
>> GCC/X64
>>
>> When using GCC to build for X64, we switched to the position independent
>> small code model, which is much more efficient in terms of code generation
>> and runtime relocation footprint, and produces binaries that can execute
>> correctly from any offset.
>>
>> However, the PIC routines are by default geared towards hosted binaries
>> containing symbol references that may resolve to definitions in other
>> dynamic objects, and for this reason, external symbol references are
>> indirected via a GOT entry by default (which also results in a .reloc fixup
>> entry) unless we annotate them.
>>
>> For this reason, we introduced the 'protected' visibility annotation for
>> all symbol definitions and references, by setting the GCC visibility
>> pragma. However, as it turns out, this is not sufficient for all versions
>> of GCC, and in some cases (GCC 5.x using the GCC49 toolchain tag), may
>> still result in GOT based relocations.
>>
>> So switch to 'hidden' visibility instead, which is slightly stronger, and
>> fixes this issue for the versions of GCC that exhibit the problem.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  MdePkg/Include/X64/ProcessorBind.h | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/MdePkg/Include/X64/ProcessorBind.h
>> b/MdePkg/Include/X64/ProcessorBind.h
>> index a4aad3e524e8..666cc8e8bd16 100644
>> --- a/MdePkg/Include/X64/ProcessorBind.h
>> +++ b/MdePkg/Include/X64/ProcessorBind.h
>> @@ -29,12 +29,12 @@
>>
>>  #if defined(__GNUC__) && defined(__pic__)
>>  //
>> -// Mark all symbol declarations and references as protected, meaning they
>> will
>> +// Mark all symbol declarations and references as hidden, meaning they will
>>  // not be subject to symbol preemption. This allows the compiler to refer to
>>  // symbols directly using relative references rather than via the GOT, which
>>  // contains absolute symbol addresses that are subject to runtime relocation.
>>  //
>> -#pragma GCC visibility push (protected)
>> +#pragma GCC visibility push (hidden)
>>  #endif
>>
>>  #if defined(__INTEL_COMPILER)
>> --
>> 2.7.4
>