From aaba098fe6ce594ae6f963dc041be6307e499f19 Mon Sep 17 00:00:00 2001 From: Andrew Murray Date: Tue, 9 Apr 2019 10:52:40 +0100 Subject: arm64: HWCAP: add support for AT_HWCAP2 As we will exhaust the first 32 bits of AT_HWCAP let's start exposing AT_HWCAP2 to userspace to give us up to 64 caps. Whilst it's possible to use the remaining 32 bits of AT_HWCAP, we prefer to expand into AT_HWCAP2 in order to provide a consistent view to userspace between ILP32 and LP64. However internal to the kernel we prefer to continue to use the full space of elf_hwcap. To reduce complexity and allow for future expansion, we now represent hwcaps in the kernel as ordinals and use a KERNEL_HWCAP_ prefix. This allows us to support automatic feature based module loading for all our hwcaps. We introduce cpu_set_feature to set hwcaps which complements the existing cpu_have_feature helper. These helpers allow us to clean up existing direct uses of elf_hwcap and reduce any future effort required to move beyond 64 caps. For convenience we also introduce cpu_{have,set}_named_feature which makes use of the cpu_feature macro to allow providing a hwcap name without a {KERNEL_}HWCAP_ prefix. Signed-off-by: Andrew Murray [will: use const_ilog2() and tweak documentation] Signed-off-by: Will Deacon --- Documentation/arm64/elf_hwcaps.txt | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) (limited to 'Documentation/arm64') diff --git a/Documentation/arm64/elf_hwcaps.txt b/Documentation/arm64/elf_hwcaps.txt index 13d6691b37bee..11805777031e7 100644 --- a/Documentation/arm64/elf_hwcaps.txt +++ b/Documentation/arm64/elf_hwcaps.txt @@ -13,9 +13,9 @@ architected discovery mechanism available to userspace code at EL0. The kernel exposes the presence of these features to userspace through a set of flags called hwcaps, exposed in the auxilliary vector. -Userspace software can test for features by acquiring the AT_HWCAP entry -of the auxilliary vector, and testing whether the relevant flags are -set, e.g. +Userspace software can test for features by acquiring the AT_HWCAP or +AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant +flags are set, e.g. bool floating_point_is_present(void) { @@ -194,3 +194,10 @@ HWCAP_PACG Functionality implied by ID_AA64ISAR1_EL1.GPA == 0b0001 or ID_AA64ISAR1_EL1.GPI == 0b0001, as described by Documentation/arm64/pointer-authentication.txt. + + +4. Unused AT_HWCAP bits +----------------------- + +For interoperation with userspace, the kernel guarantees that bits 62 +and 63 of AT_HWCAP will always be returned as 0. -- cgit v1.2.3