Re: [PATCH v4 0/7] BaseTools: add support for GCC5 in LTO mode

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

On 29 July 2016 at 08:09, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> On 29 July 2016 at 06:47, Gao, Liming <liming.gao@intel.com> wrote:
>> Ard:
>>   Thanks for your update. I have some comments for them.
>> 1) It uses GCC as Link for GCC44-GCC49. Have you done verification on them? I verify GCC49 in OVMFIa32X64 platform. It works.
>
> Yes, I tested all of them.
>
>> 2) After this change, how to append new link option in platform DSC? Use style -Wl, ?
>
> It depends. Some options (like -z) don't need it, but others do.
>
>> 3) I see GCC5 uses gcc-ar as its SLINK, and GCC49 uses ar as its SLINK. Is gcc-ar required only by LTO?
>
> Yes
>
>> 4) Before GCC49 optimization, GCC49 means GCC49 or later, GCC5 can work with GCC49 tool chain configuration. But now, I configure gcc to point to GCC5, and build OVMF with GCC49 tool chain, it reports GenFw failure. I expect GCC5 work with GCC49 and GCC5 tool chain both. GCC49 for no lto, GCC5 for lto. I know Steven has provided the patch to fix this GenFw issue.
>>
>> GenFw: ERROR 3000: Invalid
>>   /home/hwu/work/lgao4/AllPkg/Build/Ovmf3264/DEBUG_GCC49/X64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll unsupported ELF EM_X86_64 relocation 0x9.
>> GenFw: ERROR 3000: Invalid
>>   /home/hwu/work/lgao4/AllPkg/Build/Ovmf3264/DEBUG_GCC49/X64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll unsupported ELF EM_X86_64 relocation 0x9.
>> GenFw: ERROR 3000: Invalid
>>
>
> Which GCC version are you using?
>

I cannot reproduce this with gcc version 5.4.0 20160609 (Ubuntu
5.4.0-6ubuntu1~16.04.1)

In any case, I think we should merge Steven's patch that adds handling
to the relocation types to GenFw. The issue is only that having a GOT
does not make a lot of sense for UEFI executables, since it forces a
symbol reference to be absolute, which uses more space in the code,
but also in the .reloc section. The visibility pragma I introduced for
GCC4x was intended to prevent GOT based relocations from being
emitted.