Re: Warnings cross-building AARCH64 package with GCC 6.2.1 (-Wlto-type-mismatch)

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

On 9 May 2017 at 02:48, Rebecca Cran <rebecca@bluestop.org> wrote:
> I suspect I should be trying to build AARCH64 stuff with something more
> like gcc 4.8 instead of 6.2.1, but when I did build the
> Overdrive1000Board package I saw lots of warnings complaining about the
> implementation not matching the prototype (with
> the warning being -Wlto-type-mismatch).
>
> I cross-compiled on an OpenSUSE x64 system with
> aarch64-suse-linux-gcc-6, with the commandline:
>
> build -a AARCH64 -t GCC5 -b RELEASE -p
> OpenPlatformPkg/Platforms/AMD/Styx/Overdrive1000Board/Overdrive1000Board.dsc
>
> ArmPlatformPkg is from
> linaro git master, edk2 is tianocore git master
>
> The warnings were all similar to:
>
> /workspace/edk2/MdePkg/Include/Library/BaseMemoryLib.h:462:1:
> warning: type of 'IsZeroGuid' does not match original declaration
> [-Wlto-type-mismatch] IsZeroGuid ( ^
> //workspace/edk2/MdePkg/Library/BaseMemoryLibOptDxe/Arm/MemLibGuid.c:158:1:
> note: 'IsZeroGuid' was previously declared here IsZeroGuid (
>  ^
> /workspace/edk2/MdePkg/Library/BaseMemoryLibOptDxe/Arm/MemLibGuid.c:158:1:
> note: code may be misoptimized unless -fno-strict-aliasing is used
>
>
>
> Are these real problems, or just because gcc 6.2 and/or LTO aren't ready
> for AARCH64 yet?
>

Hi,

This issue is caused by the fact that some libraries are built with
-mstrict-align on AArch64. This is necessary since code that may
execute with the MMU off should not use unaligned access, which GCC
may emit by default for AArch64 targets.