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author | Dmitry Torokhov <dmitry.torokhov@gmail.com> | 2018-02-01 00:41:33 -0800 |
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committer | Dmitry Torokhov <dmitry.torokhov@gmail.com> | 2018-02-01 00:41:33 -0800 |
commit | 10a558374f3751cf4eb55143008975641dfc2cf4 (patch) | |
tree | aab0def9d2289f6520ffb62ec4c1d738135447c4 /Documentation/arm64/elf_hwcaps.txt | |
parent | fafef982c7353e8982b951e40573e990ccf0ed00 (diff) | |
parent | d8a5b80568a9cb66810e75b182018e9edb68e8ff (diff) | |
download | linux-10a558374f3751cf4eb55143008975641dfc2cf4.tar.bz2 |
Merge tag 'v4.15' into next
Sync with mainline to get in trackpoint updates and other changes.
Diffstat (limited to 'Documentation/arm64/elf_hwcaps.txt')
-rw-r--r-- | Documentation/arm64/elf_hwcaps.txt | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/Documentation/arm64/elf_hwcaps.txt b/Documentation/arm64/elf_hwcaps.txt new file mode 100644 index 000000000000..89edba12a9e0 --- /dev/null +++ b/Documentation/arm64/elf_hwcaps.txt @@ -0,0 +1,160 @@ +ARM64 ELF hwcaps +================ + +This document describes the usage and semantics of the arm64 ELF hwcaps. + + +1. Introduction +--------------- + +Some hardware or software features are only available on some CPU +implementations, and/or with certain kernel configurations, but have no +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. + +bool floating_point_is_present(void) +{ + unsigned long hwcaps = getauxval(AT_HWCAP); + if (hwcaps & HWCAP_FP) + return true; + + return false; +} + +Where software relies on a feature described by a hwcap, it should check +the relevant hwcap flag to verify that the feature is present before +attempting to make use of the feature. + +Features cannot be probed reliably through other means. When a feature +is not available, attempting to use it may result in unpredictable +behaviour, and is not guaranteed to result in any reliable indication +that the feature is unavailable, such as a SIGILL. + + +2. Interpretation of hwcaps +--------------------------- + +The majority of hwcaps are intended to indicate the presence of features +which are described by architected ID registers inaccessible to +userspace code at EL0. These hwcaps are defined in terms of ID register +fields, and should be interpreted with reference to the definition of +these fields in the ARM Architecture Reference Manual (ARM ARM). + +Such hwcaps are described below in the form: + + Functionality implied by idreg.field == val. + +Such hwcaps indicate the availability of functionality that the ARM ARM +defines as being present when idreg.field has value val, but do not +indicate that idreg.field is precisely equal to val, nor do they +indicate the absence of functionality implied by other values of +idreg.field. + +Other hwcaps may indicate the presence of features which cannot be +described by ID registers alone. These may be described without +reference to ID registers, and may refer to other documentation. + + +3. The hwcaps exposed in AT_HWCAP +--------------------------------- + +HWCAP_FP + + Functionality implied by ID_AA64PFR0_EL1.FP == 0b0000. + +HWCAP_ASIMD + + Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0000. + +HWCAP_EVTSTRM + + The generic timer is configured to generate events at a frequency of + approximately 100KHz. + +HWCAP_AES + + Functionality implied by ID_AA64ISAR1_EL1.AES == 0b0001. + +HWCAP_PMULL + + Functionality implied by ID_AA64ISAR1_EL1.AES == 0b0010. + +HWCAP_SHA1 + + Functionality implied by ID_AA64ISAR0_EL1.SHA1 == 0b0001. + +HWCAP_SHA2 + + Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0001. + +HWCAP_CRC32 + + Functionality implied by ID_AA64ISAR0_EL1.CRC32 == 0b0001. + +HWCAP_ATOMICS + + Functionality implied by ID_AA64ISAR0_EL1.Atomic == 0b0010. + +HWCAP_FPHP + + Functionality implied by ID_AA64PFR0_EL1.FP == 0b0001. + +HWCAP_ASIMDHP + + Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0001. + +HWCAP_CPUID + + EL0 access to certain ID registers is available, to the extent + described by Documentation/arm64/cpu-feature-registers.txt. + + These ID registers may imply the availability of features. + +HWCAP_ASIMDRDM + + Functionality implied by ID_AA64ISAR0_EL1.RDM == 0b0001. + +HWCAP_JSCVT + + Functionality implied by ID_AA64ISAR1_EL1.JSCVT == 0b0001. + +HWCAP_FCMA + + Functionality implied by ID_AA64ISAR1_EL1.FCMA == 0b0001. + +HWCAP_LRCPC + + Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0001. + +HWCAP_DCPOP + + Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0001. + +HWCAP_SHA3 + + Functionality implied by ID_AA64ISAR0_EL1.SHA3 == 0b0001. + +HWCAP_SM3 + + Functionality implied by ID_AA64ISAR0_EL1.SM3 == 0b0001. + +HWCAP_SM4 + + Functionality implied by ID_AA64ISAR0_EL1.SM4 == 0b0001. + +HWCAP_ASIMDDP + + Functionality implied by ID_AA64ISAR0_EL1.DP == 0b0001. + +HWCAP_SHA512 + + Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0002. + +HWCAP_SVE + + Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001. |