From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Murray Subject: [PATCH v3 7/7] arm64: docs: document AT_HWCAP2 and unused AT_HWCAP bits Date: Mon, 1 Apr 2019 11:45:15 +0100 Message-ID: <20190401104515.39775-8-andrew.murray@arm.com> References: <20190401104515.39775-1-andrew.murray@arm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org In-Reply-To: <20190401104515.39775-1-andrew.murray@arm.com> To: Catalin Marinas , Will Deacon Cc: Szabolcs Nagy , dave.martin@arm.com, linux-arm-kernel@lists.infradead.org, Mark Rutland , Phil Blundell , libc-alpha@sourceware.org, linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org Now that we have expanded into AT_HWCAP2 let's add some documentation to describe its presence. We also document the unused top half of AT_HWCAP which we always return as 0 for userspace interoperation. Signed-off-by: Andrew Murray --- Documentation/arm64/elf_hwcaps.txt | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/Documentation/arm64/elf_hwcaps.txt b/Documentation/arm64/elf_hwcaps.txt index c605757dd4db..6b3d4d334db7 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) { @@ -198,3 +198,11 @@ 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 +----------------------- + +Each AT_HWCAP and AT_HWCAP2 entry provides for up to 32 hwcaps contained +in bits [31:0]. For interoperation with userspace we guarantee that bit +62 of AT_HWCAP will always be returned as 0. -- 2.21.0