0001 .. _elf_hwcaps_index:
0002
0003 ================
0004 ARM64 ELF hwcaps
0005 ================
0006
0007 This document describes the usage and semantics of the arm64 ELF hwcaps.
0008
0009
0010 1. Introduction
0011 ---------------
0012
0013 Some hardware or software features are only available on some CPU
0014 implementations, and/or with certain kernel configurations, but have no
0015 architected discovery mechanism available to userspace code at EL0. The
0016 kernel exposes the presence of these features to userspace through a set
0017 of flags called hwcaps, exposed in the auxilliary vector.
0018
0019 Userspace software can test for features by acquiring the AT_HWCAP or
0020 AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant
0021 flags are set, e.g.::
0022
0023 bool floating_point_is_present(void)
0024 {
0025 unsigned long hwcaps = getauxval(AT_HWCAP);
0026 if (hwcaps & HWCAP_FP)
0027 return true;
0028
0029 return false;
0030 }
0031
0032 Where software relies on a feature described by a hwcap, it should check
0033 the relevant hwcap flag to verify that the feature is present before
0034 attempting to make use of the feature.
0035
0036 Features cannot be probed reliably through other means. When a feature
0037 is not available, attempting to use it may result in unpredictable
0038 behaviour, and is not guaranteed to result in any reliable indication
0039 that the feature is unavailable, such as a SIGILL.
0040
0041
0042 2. Interpretation of hwcaps
0043 ---------------------------
0044
0045 The majority of hwcaps are intended to indicate the presence of features
0046 which are described by architected ID registers inaccessible to
0047 userspace code at EL0. These hwcaps are defined in terms of ID register
0048 fields, and should be interpreted with reference to the definition of
0049 these fields in the ARM Architecture Reference Manual (ARM ARM).
0050
0051 Such hwcaps are described below in the form::
0052
0053 Functionality implied by idreg.field == val.
0054
0055 Such hwcaps indicate the availability of functionality that the ARM ARM
0056 defines as being present when idreg.field has value val, but do not
0057 indicate that idreg.field is precisely equal to val, nor do they
0058 indicate the absence of functionality implied by other values of
0059 idreg.field.
0060
0061 Other hwcaps may indicate the presence of features which cannot be
0062 described by ID registers alone. These may be described without
0063 reference to ID registers, and may refer to other documentation.
0064
0065
0066 3. The hwcaps exposed in AT_HWCAP
0067 ---------------------------------
0068
0069 HWCAP_FP
0070 Functionality implied by ID_AA64PFR0_EL1.FP == 0b0000.
0071
0072 HWCAP_ASIMD
0073 Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0000.
0074
0075 HWCAP_EVTSTRM
0076 The generic timer is configured to generate events at a frequency of
0077 approximately 10KHz.
0078
0079 HWCAP_AES
0080 Functionality implied by ID_AA64ISAR0_EL1.AES == 0b0001.
0081
0082 HWCAP_PMULL
0083 Functionality implied by ID_AA64ISAR0_EL1.AES == 0b0010.
0084
0085 HWCAP_SHA1
0086 Functionality implied by ID_AA64ISAR0_EL1.SHA1 == 0b0001.
0087
0088 HWCAP_SHA2
0089 Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0001.
0090
0091 HWCAP_CRC32
0092 Functionality implied by ID_AA64ISAR0_EL1.CRC32 == 0b0001.
0093
0094 HWCAP_ATOMICS
0095 Functionality implied by ID_AA64ISAR0_EL1.Atomic == 0b0010.
0096
0097 HWCAP_FPHP
0098 Functionality implied by ID_AA64PFR0_EL1.FP == 0b0001.
0099
0100 HWCAP_ASIMDHP
0101 Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0001.
0102
0103 HWCAP_CPUID
0104 EL0 access to certain ID registers is available, to the extent
0105 described by Documentation/arm64/cpu-feature-registers.rst.
0106
0107 These ID registers may imply the availability of features.
0108
0109 HWCAP_ASIMDRDM
0110 Functionality implied by ID_AA64ISAR0_EL1.RDM == 0b0001.
0111
0112 HWCAP_JSCVT
0113 Functionality implied by ID_AA64ISAR1_EL1.JSCVT == 0b0001.
0114
0115 HWCAP_FCMA
0116 Functionality implied by ID_AA64ISAR1_EL1.FCMA == 0b0001.
0117
0118 HWCAP_LRCPC
0119 Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0001.
0120
0121 HWCAP_DCPOP
0122 Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0001.
0123
0124 HWCAP_SHA3
0125 Functionality implied by ID_AA64ISAR0_EL1.SHA3 == 0b0001.
0126
0127 HWCAP_SM3
0128 Functionality implied by ID_AA64ISAR0_EL1.SM3 == 0b0001.
0129
0130 HWCAP_SM4
0131 Functionality implied by ID_AA64ISAR0_EL1.SM4 == 0b0001.
0132
0133 HWCAP_ASIMDDP
0134 Functionality implied by ID_AA64ISAR0_EL1.DP == 0b0001.
0135
0136 HWCAP_SHA512
0137 Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0010.
0138
0139 HWCAP_SVE
0140 Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001.
0141
0142 HWCAP_ASIMDFHM
0143 Functionality implied by ID_AA64ISAR0_EL1.FHM == 0b0001.
0144
0145 HWCAP_DIT
0146 Functionality implied by ID_AA64PFR0_EL1.DIT == 0b0001.
0147
0148 HWCAP_USCAT
0149 Functionality implied by ID_AA64MMFR2_EL1.AT == 0b0001.
0150
0151 HWCAP_ILRCPC
0152 Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0010.
0153
0154 HWCAP_FLAGM
0155 Functionality implied by ID_AA64ISAR0_EL1.TS == 0b0001.
0156
0157 HWCAP_SSBS
0158 Functionality implied by ID_AA64PFR1_EL1.SSBS == 0b0010.
0159
0160 HWCAP_SB
0161 Functionality implied by ID_AA64ISAR1_EL1.SB == 0b0001.
0162
0163 HWCAP_PACA
0164 Functionality implied by ID_AA64ISAR1_EL1.APA == 0b0001 or
0165 ID_AA64ISAR1_EL1.API == 0b0001, as described by
0166 Documentation/arm64/pointer-authentication.rst.
0167
0168 HWCAP_PACG
0169 Functionality implied by ID_AA64ISAR1_EL1.GPA == 0b0001 or
0170 ID_AA64ISAR1_EL1.GPI == 0b0001, as described by
0171 Documentation/arm64/pointer-authentication.rst.
0172
0173 HWCAP2_DCPODP
0174 Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0010.
0175
0176 HWCAP2_SVE2
0177 Functionality implied by ID_AA64ZFR0_EL1.SVEVer == 0b0001.
0178
0179 HWCAP2_SVEAES
0180 Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0001.
0181
0182 HWCAP2_SVEPMULL
0183 Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0010.
0184
0185 HWCAP2_SVEBITPERM
0186 Functionality implied by ID_AA64ZFR0_EL1.BitPerm == 0b0001.
0187
0188 HWCAP2_SVESHA3
0189 Functionality implied by ID_AA64ZFR0_EL1.SHA3 == 0b0001.
0190
0191 HWCAP2_SVESM4
0192 Functionality implied by ID_AA64ZFR0_EL1.SM4 == 0b0001.
0193
0194 HWCAP2_FLAGM2
0195 Functionality implied by ID_AA64ISAR0_EL1.TS == 0b0010.
0196
0197 HWCAP2_FRINT
0198 Functionality implied by ID_AA64ISAR1_EL1.FRINTTS == 0b0001.
0199
0200 HWCAP2_SVEI8MM
0201 Functionality implied by ID_AA64ZFR0_EL1.I8MM == 0b0001.
0202
0203 HWCAP2_SVEF32MM
0204 Functionality implied by ID_AA64ZFR0_EL1.F32MM == 0b0001.
0205
0206 HWCAP2_SVEF64MM
0207 Functionality implied by ID_AA64ZFR0_EL1.F64MM == 0b0001.
0208
0209 HWCAP2_SVEBF16
0210 Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0001.
0211
0212 HWCAP2_I8MM
0213 Functionality implied by ID_AA64ISAR1_EL1.I8MM == 0b0001.
0214
0215 HWCAP2_BF16
0216 Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0001.
0217
0218 HWCAP2_DGH
0219 Functionality implied by ID_AA64ISAR1_EL1.DGH == 0b0001.
0220
0221 HWCAP2_RNG
0222 Functionality implied by ID_AA64ISAR0_EL1.RNDR == 0b0001.
0223
0224 HWCAP2_BTI
0225 Functionality implied by ID_AA64PFR0_EL1.BT == 0b0001.
0226
0227 HWCAP2_MTE
0228 Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0010, as described
0229 by Documentation/arm64/memory-tagging-extension.rst.
0230
0231 HWCAP2_ECV
0232 Functionality implied by ID_AA64MMFR0_EL1.ECV == 0b0001.
0233
0234 HWCAP2_AFP
0235 Functionality implied by ID_AA64MFR1_EL1.AFP == 0b0001.
0236
0237 HWCAP2_RPRES
0238 Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001.
0239
0240 HWCAP2_MTE3
0241 Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0011, as described
0242 by Documentation/arm64/memory-tagging-extension.rst.
0243
0244 HWCAP2_SME
0245 Functionality implied by ID_AA64PFR1_EL1.SME == 0b0001, as described
0246 by Documentation/arm64/sme.rst.
0247
0248 HWCAP2_SME_I16I64
0249 Functionality implied by ID_AA64SMFR0_EL1.I16I64 == 0b1111.
0250
0251 HWCAP2_SME_F64F64
0252 Functionality implied by ID_AA64SMFR0_EL1.F64F64 == 0b1.
0253
0254 HWCAP2_SME_I8I32
0255 Functionality implied by ID_AA64SMFR0_EL1.I8I32 == 0b1111.
0256
0257 HWCAP2_SME_F16F32
0258 Functionality implied by ID_AA64SMFR0_EL1.F16F32 == 0b1.
0259
0260 HWCAP2_SME_B16F32
0261 Functionality implied by ID_AA64SMFR0_EL1.B16F32 == 0b1.
0262
0263 HWCAP2_SME_F32F32
0264 Functionality implied by ID_AA64SMFR0_EL1.F32F32 == 0b1.
0265
0266 HWCAP2_SME_FA64
0267 Functionality implied by ID_AA64SMFR0_EL1.FA64 == 0b1.
0268
0269 HWCAP2_WFXT
0270 Functionality implied by ID_AA64ISAR2_EL1.WFXT == 0b0010.
0271
0272 HWCAP2_EBF16
0273 Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0010.
0274
0275 4. Unused AT_HWCAP bits
0276 -----------------------
0277
0278 For interoperation with userspace, the kernel guarantees that bits 62
0279 and 63 of AT_HWCAP will always be returned as 0.
