powerpc/64s: Fix NULL AT_BASE_PLATFORM when using DT CPU features

[Michael Ellerman]

On Tue, 2018-03-13 at 23:14:11 UTC, Michael Ellerman wrote:
> When running virtualised the powerpc kernel is able to run the system
> in "compat mode" - which means the kernel and hardware are pretending
> to userspace that the CPU is an older version than it actually is.
> 
> AT_BASE_PLATFORM is an AUXV entry that we export to userspace for use
> when we're running in that mode, which tells userspace the "platform"
> string for the real CPU version, as opposed to the faked version.
> 
> Although we don't support compat mode when using DT CPU features, and
> arguably don't need to set AT_BASE_PLATFORM, the existing cputable
> based code always sets it even when we're running bare metal. That
> means the lack of AT_BASE_PLATFORM is a user-visible artifact of the
> fact that the kernel is using DT CPU features, which we don't want.
> 
> So set it in the DT CPU features code also.
> 
> This results in eg:
>   $ LD_SHOW_AUXV=1 /bin/true | grep "AT_.*PLATFORM"
>   AT_PLATFORM:     power9
>   AT_BASE_PLATFORM:power9
> 
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/e4b79900222b8cccd4da4a7a89581f

cheers