Re: [PATCH 2/2] ArmVirtPkg ARM: make relocatable PrePi users build with CLANG35

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

On 3 August 2016 at 12:00, Laszlo Ersek <lersek@redhat.com> wrote:
> On 08/03/16 10:21, Ard Biesheuvel wrote:
>> The clang developers have made a backward incompatible change to the
>> command line arguments, and have replaced '-mllvm -arm-use-movt=0'
>> with '-mno-movt'. This does not matter for most ARM platforms, and
>> therefore it has been removed from the default CLANG35/ARM CC flags
>> in patch 1c63516075b3 ("BaseTools CLANG35: drop problematic use-movt
>> and save-temps options"), but as it turns out, the relocatable PrePi
>> implementation used by ArmVirtQemuKernel and ArmVirtXen will fail to
>> build if it contains MOVT/MOVW pairs, due to the fact that these are
>> not runtime relocatable under ELF.
>>
>> Since they are runtime relocatable under PE/COFF, and GenFw does the
>> right thing when encountering them, selectively controlling their
>> use is more appropriate than disabling them altogether. Therefore,
>> this patch adds the -mno-movt argument only for the platforms that
>> use the relocatable PrePi, and only for the module types that may
>> be pulled into its build.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  ArmVirtPkg/ArmVirtQemuKernel.dsc | 8 ++++++++
>>  ArmVirtPkg/ArmVirtXen.dsc        | 9 +++++++++
>>  2 files changed, 17 insertions(+)
>>
>> diff --git a/ArmVirtPkg/ArmVirtQemuKernel.dsc b/ArmVirtPkg/ArmVirtQemuKernel.dsc
>> index 01a1d9b4613b..6c536d9bbd2d 100644
>> --- a/ArmVirtPkg/ArmVirtQemuKernel.dsc
>> +++ b/ArmVirtPkg/ArmVirtQemuKernel.dsc
>> @@ -45,6 +45,9 @@ [LibraryClasses.ARM]
>>    ArmLib|ArmPkg/Library/ArmLib/ArmV7/ArmV7Lib.inf
>>    ArmCpuLib|ArmPkg/Drivers/ArmCpuLib/ArmCortexA15Lib/ArmCortexA15Lib.inf
>>
>> +[LibraryClasses.ARM.SEC]
>> +  ArmLib|ArmPkg/Library/ArmLib/ArmV7/ArmV7LibSec.inf
>> +
>
> How does this library resolution change relate to the stated purpose of
> the patch?
>

It prevents a version of ArmLib being pulled into the build of the
relocatable PrePi that was built using the BuildOptions for DXE_DRIVER
type modules.

-- 
Ard.