Re: swp on armv8 (Was: Haskell on arm needs help)
On Wed, 2014-12-03 at 23:23 +0000, peter green wrote:
> I vaugely remember something a while back about some deprecated 32-bit
> arm instructions needing kernel emulation on armv8 and that emulation
> not being implemented yet.
That's correct, and IIRC swp is one of those instructions.
> AIUI swp is already handled through kernel emulation on armv7
> multiprocessor systems. There seem to be patches to port that emulation
> to arm64 but it doesn't appear they are in the kernel tree debian is
> using.
> Having 32-bit binaries break on armv8 systems due to lack of the
> swp instruction does not seem like a good thing so IMO we really want
> this in our kernels before release.
If those patches have gone into a later upstream kernel than we have in
Jessie (v3.16) then we should certainly backport them. IIRC they were
controversial though, so if they haven't hit mainline I'd be *very*
reluctant to "fork" the v8 userspace ABI.
Ian.
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