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1.. _elf_hwcaps_index:
2
3================
4ARM64 ELF hwcaps
5================
6
7This document describes the usage and semantics of the arm64 ELF hwcaps.
8
9
101. Introduction
11---------------
12
13Some hardware or software features are only available on some CPU
14implementations, and/or with certain kernel configurations, but have no
15architected discovery mechanism available to userspace code at EL0. The
16kernel exposes the presence of these features to userspace through a set
17of flags called hwcaps, exposed in the auxilliary vector.
18
19Userspace software can test for features by acquiring the AT_HWCAP or
20AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant
21flags are set, e.g.::
22
23 bool floating_point_is_present(void)
24 {
25 unsigned long hwcaps = getauxval(AT_HWCAP);
26 if (hwcaps & HWCAP_FP)
27 return true;
28
29 return false;
30 }
31
32Where software relies on a feature described by a hwcap, it should check
33the relevant hwcap flag to verify that the feature is present before
34attempting to make use of the feature.
35
36Features cannot be probed reliably through other means. When a feature
37is not available, attempting to use it may result in unpredictable
38behaviour, and is not guaranteed to result in any reliable indication
39that the feature is unavailable, such as a SIGILL.
40
41
422. Interpretation of hwcaps
43---------------------------
44
45The majority of hwcaps are intended to indicate the presence of features
46which are described by architected ID registers inaccessible to
47userspace code at EL0. These hwcaps are defined in terms of ID register
48fields, and should be interpreted with reference to the definition of
49these fields in the ARM Architecture Reference Manual (ARM ARM).
50
51Such hwcaps are described below in the form::
52
53 Functionality implied by idreg.field == val.
54
55Such hwcaps indicate the availability of functionality that the ARM ARM
56defines as being present when idreg.field has value val, but do not
57indicate that idreg.field is precisely equal to val, nor do they
58indicate the absence of functionality implied by other values of
59idreg.field.
60
61Other hwcaps may indicate the presence of features which cannot be
62described by ID registers alone. These may be described without
63reference to ID registers, and may refer to other documentation.
64
65
663. The hwcaps exposed in AT_HWCAP
67---------------------------------
68
69HWCAP_FP
70 Functionality implied by ID_AA64PFR0_EL1.FP == 0b0000.
71
72HWCAP_ASIMD
73 Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0000.
74
75HWCAP_EVTSTRM
76 The generic timer is configured to generate events at a frequency of
77 approximately 10KHz.
78
79HWCAP_AES
80 Functionality implied by ID_AA64ISAR0_EL1.AES == 0b0001.
81
82HWCAP_PMULL
83 Functionality implied by ID_AA64ISAR0_EL1.AES == 0b0010.
84
85HWCAP_SHA1
86 Functionality implied by ID_AA64ISAR0_EL1.SHA1 == 0b0001.
87
88HWCAP_SHA2
89 Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0001.
90
91HWCAP_CRC32
92 Functionality implied by ID_AA64ISAR0_EL1.CRC32 == 0b0001.
93
94HWCAP_ATOMICS
95 Functionality implied by ID_AA64ISAR0_EL1.Atomic == 0b0010.
96
97HWCAP_FPHP
98 Functionality implied by ID_AA64PFR0_EL1.FP == 0b0001.
99
100HWCAP_ASIMDHP
101 Functionality implied by ID_AA64PFR0_EL1.AdvSIMD == 0b0001.
102
103HWCAP_CPUID
104 EL0 access to certain ID registers is available, to the extent
105 described by Documentation/arm64/cpu-feature-registers.rst.
106
107 These ID registers may imply the availability of features.
108
109HWCAP_ASIMDRDM
110 Functionality implied by ID_AA64ISAR0_EL1.RDM == 0b0001.
111
112HWCAP_JSCVT
113 Functionality implied by ID_AA64ISAR1_EL1.JSCVT == 0b0001.
114
115HWCAP_FCMA
116 Functionality implied by ID_AA64ISAR1_EL1.FCMA == 0b0001.
117
118HWCAP_LRCPC
119 Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0001.
120
121HWCAP_DCPOP
122 Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0001.
123
124HWCAP_SHA3
125 Functionality implied by ID_AA64ISAR0_EL1.SHA3 == 0b0001.
126
127HWCAP_SM3
128 Functionality implied by ID_AA64ISAR0_EL1.SM3 == 0b0001.
129
130HWCAP_SM4
131 Functionality implied by ID_AA64ISAR0_EL1.SM4 == 0b0001.
132
133HWCAP_ASIMDDP
134 Functionality implied by ID_AA64ISAR0_EL1.DP == 0b0001.
135
136HWCAP_SHA512
137 Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0010.
138
139HWCAP_SVE
140 Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001.
141
142HWCAP_ASIMDFHM
143 Functionality implied by ID_AA64ISAR0_EL1.FHM == 0b0001.
144
145HWCAP_DIT
146 Functionality implied by ID_AA64PFR0_EL1.DIT == 0b0001.
147
148HWCAP_USCAT
149 Functionality implied by ID_AA64MMFR2_EL1.AT == 0b0001.
150
151HWCAP_ILRCPC
152 Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0010.
153
154HWCAP_FLAGM
155 Functionality implied by ID_AA64ISAR0_EL1.TS == 0b0001.
156
157HWCAP_SSBS
158 Functionality implied by ID_AA64PFR1_EL1.SSBS == 0b0010.
159
160HWCAP_SB
161 Functionality implied by ID_AA64ISAR1_EL1.SB == 0b0001.
162
163HWCAP_PACA
164 Functionality implied by ID_AA64ISAR1_EL1.APA == 0b0001 or
165 ID_AA64ISAR1_EL1.API == 0b0001, as described by
166 Documentation/arm64/pointer-authentication.rst.
167
168HWCAP_PACG
169 Functionality implied by ID_AA64ISAR1_EL1.GPA == 0b0001 or
170 ID_AA64ISAR1_EL1.GPI == 0b0001, as described by
171 Documentation/arm64/pointer-authentication.rst.
172
173HWCAP2_DCPODP
174 Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0010.
175
176HWCAP2_SVE2
177 Functionality implied by ID_AA64ZFR0_EL1.SVEVer == 0b0001.
178
179HWCAP2_SVEAES
180 Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0001.
181
182HWCAP2_SVEPMULL
183 Functionality implied by ID_AA64ZFR0_EL1.AES == 0b0010.
184
185HWCAP2_SVEBITPERM
186 Functionality implied by ID_AA64ZFR0_EL1.BitPerm == 0b0001.
187
188HWCAP2_SVESHA3
189 Functionality implied by ID_AA64ZFR0_EL1.SHA3 == 0b0001.
190
191HWCAP2_SVESM4
192 Functionality implied by ID_AA64ZFR0_EL1.SM4 == 0b0001.
193
194HWCAP2_FLAGM2
195 Functionality implied by ID_AA64ISAR0_EL1.TS == 0b0010.
196
197HWCAP2_FRINT
198 Functionality implied by ID_AA64ISAR1_EL1.FRINTTS == 0b0001.
199
200HWCAP2_SVEI8MM
201 Functionality implied by ID_AA64ZFR0_EL1.I8MM == 0b0001.
202
203HWCAP2_SVEF32MM
204 Functionality implied by ID_AA64ZFR0_EL1.F32MM == 0b0001.
205
206HWCAP2_SVEF64MM
207 Functionality implied by ID_AA64ZFR0_EL1.F64MM == 0b0001.
208
209HWCAP2_SVEBF16
210 Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0001.
211
212HWCAP2_I8MM
213 Functionality implied by ID_AA64ISAR1_EL1.I8MM == 0b0001.
214
215HWCAP2_BF16
216 Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0001.
217
218HWCAP2_DGH
219 Functionality implied by ID_AA64ISAR1_EL1.DGH == 0b0001.
220
221HWCAP2_RNG
222 Functionality implied by ID_AA64ISAR0_EL1.RNDR == 0b0001.
223
224HWCAP2_BTI
225 Functionality implied by ID_AA64PFR0_EL1.BT == 0b0001.
226
227HWCAP2_MTE
228 Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0010, as described
229 by Documentation/arm64/memory-tagging-extension.rst.
230
231HWCAP2_ECV
232 Functionality implied by ID_AA64MMFR0_EL1.ECV == 0b0001.
233
234HWCAP2_AFP
235 Functionality implied by ID_AA64MFR1_EL1.AFP == 0b0001.
236
237HWCAP2_RPRES
238 Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001.
239
240HWCAP2_MTE3
241 Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0011, as described
242 by Documentation/arm64/memory-tagging-extension.rst.
243
244HWCAP2_SME
245 Functionality implied by ID_AA64PFR1_EL1.SME == 0b0001, as described
246 by Documentation/arm64/sme.rst.
247
248HWCAP2_SME_I16I64
249 Functionality implied by ID_AA64SMFR0_EL1.I16I64 == 0b1111.
250
251HWCAP2_SME_F64F64
252 Functionality implied by ID_AA64SMFR0_EL1.F64F64 == 0b1.
253
254HWCAP2_SME_I8I32
255 Functionality implied by ID_AA64SMFR0_EL1.I8I32 == 0b1111.
256
257HWCAP2_SME_F16F32
258 Functionality implied by ID_AA64SMFR0_EL1.F16F32 == 0b1.
259
260HWCAP2_SME_B16F32
261 Functionality implied by ID_AA64SMFR0_EL1.B16F32 == 0b1.
262
263HWCAP2_SME_F32F32
264 Functionality implied by ID_AA64SMFR0_EL1.F32F32 == 0b1.
265
266HWCAP2_SME_FA64
267 Functionality implied by ID_AA64SMFR0_EL1.FA64 == 0b1.
268
269HWCAP2_WFXT
270 Functionality implied by ID_AA64ISAR2_EL1.WFXT == 0b0010.
271
272HWCAP2_EBF16
273 Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0010.
274
275HWCAP2_SVE_EBF16
276 Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0010.
277
278HWCAP2_CSSC
279 Functionality implied by ID_AA64ISAR2_EL1.CSSC == 0b0001.
280
281HWCAP2_RPRFM
282 Functionality implied by ID_AA64ISAR2_EL1.RPRFM == 0b0001.
283
284HWCAP2_SVE2P1
285 Functionality implied by ID_AA64ZFR0_EL1.SVEver == 0b0010.
286
2874. Unused AT_HWCAP bits
288-----------------------
289
290For interoperation with userspace, the kernel guarantees that bits 62
291and 63 of AT_HWCAP will always be returned as 0.