On 2/15/24 2:16 AM, Arnd Bergmann wrote: > On Wed, Feb 14, 2024, at 23:34, Peter Bergner wrote: >> The powerpc toolchain keeps a copy of the HWCAP bit masks in our TCB for fast >> access by the __builtin_cpu_supports built-in function. The TCB space for >> the HWCAP entries - which are created in pairs - is an ABI extension, so >> waiting to create the space for HWCAP3 and HWCAP4 until we need them is >> problematical. Define AT_HWCAP3 and AT_HWCAP4 in the generic uapi header >> so they can be used in glibc to reserve space in the powerpc TCB for their >> future use. >> >> I scanned through the Linux and GLIBC source codes looking for unused AT_* >> values and 29 and 30 did not seem to be used, so they are what I went >> with. This has received Acked-by's from both GLIBC and Linux kernel >> developers and no reservations or Nacks from anyone. >> >> Arnd, we seem to have consensus on the patch below. Is this something >> you could take and apply to your tree? >> > > I don't mind taking it, but it may be better to use the > powerpc tree if that is where it's actually being used. So this is not a powerpc only patch, but we may be the first arch to use it. Szabolcs mentioned that aarch64 was pretty quickly filling up their AT_HWCAP2 and that they will eventually require using AT_HWCAP3 as well. If you still think this should go through the powerpc tree, I can check on that. Peter
