Re: [PATCH 0/2] arm64/sve: Fix mutating register endianness on big-endian

On Fri, Jun 07, 2019 at 10:38:58AM +0100, Will Deacon wrote:
> On Thu, Jun 06, 2019 at 05:44:53PM +0100, Dave Martin wrote:
> > By inspection while debugging something else, I noticed that the byte
> > order of FPSIMD V-register stores and SVE Z-register stores is not the
> > same when running on big-endian.
> > 
> > This is not properly taken into account when moving between the FPSIMD
> > and SVE register views inside the kernel, resulting in the bytes of a
> > V-register getting spontaneously reversed in some situations, from
> > userspace's point of view.  The signal frame and ptrace interface are
> > also affected.  The KVM ABI forbids mixing the two views and so should
> > not be affected.
> > 
> > See patch 2 for details.
> > 
> > Patch 1 does some trivial preparatory refactoring.
> 
> Sorry to be a pain, but would you be able to flip this series round so that
> the fix doesn't depend on the refactoring, please? That way we can put it
> into stable without the dependency.
> 
> > gdb may or may not be affected by this, depending on how it uses the
> > NT_PRFPREG and NT_ARM_SVE regsets.  I'll leave it to the developers to
> > assess that.
> 
> Wouldn't this be easy enough to test?

So, gdb works OK on big-endian but weird stuff happening on both with
and without the fix.

There are places in the gdb code itself where it is likely missing
endianness conversions, but I need to follow up with the gdb folks to
clarify whether my patch is missing something...

Cheers
---Dave