Peter Bergner <bergner@xxxxxxxxxxxxx> writes:
> 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.
I'm happy to take it with Arnd's ack.
I trimmed up the commit message a bit, see below.
cheers
Author: Peter Bergner <bergner@xxxxxxxxxxxxx>
AuthorDate: Wed Feb 14 16:34:06 2024 -0600
Commit: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
CommitDate: Fri Feb 16 12:42:59 2024 +1100
uapi/auxvec: Define AT_HWCAP3 and AT_HWCAP4 aux vector, entries
The powerpc toolchain keeps a copy of the HWCAP bit masks in the 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
they are needed is problematic. 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.
Signed-off-by: Peter Bergner <bergner@xxxxxxxxxxxxx>
Acked-by: Adhemerval Zanella <adhemerval.zanella@xxxxxxxxxx>
Acked-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Acked-by: Szabolcs Nagy <szabolcs.nagy@xxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/a406b535-dc55-4856-8ae9-5a063644a1af@xxxxxxxxxxxxx
