1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_ALTERNATIVE_H
3 #define __ASM_ALTERNATIVE_H
4
5 #include <asm/cpucaps.h>
6 #include <asm/insn.h>
7
8 #define ARM64_CB_PATCH ARM64_NCAPS
9
10 #ifndef __ASSEMBLY__
11
12 #include <linux/init.h>
13 #include <linux/types.h>
14 #include <linux/stddef.h>
15 #include <linux/stringify.h>
16
17 extern int alternatives_applied;
18
19 struct alt_instr {
20 s32 orig_offset; /* offset to original instruction */
21 s32 alt_offset; /* offset to replacement instruction */
22 u16 cpufeature; /* cpufeature bit set for replacement */
23 u8 orig_len; /* size of original instruction(s) */
24 u8 alt_len; /* size of new instruction(s), <= orig_len */
25 };
26
27 typedef void (*alternative_cb_t)(struct alt_instr *alt,
28 __le32 *origptr, __le32 *updptr, int nr_inst);
29
30 void __init apply_alternatives_all(void);
31
32 #ifdef CONFIG_MODULES
33 void apply_alternatives_module(void *start, size_t length);
34 #else
apply_alternatives_module(void * start,size_t length)35 static inline void apply_alternatives_module(void *start, size_t length) { }
36 #endif
37
38 #define ALTINSTR_ENTRY(feature,cb) \
39 " .word 661b - .\n" /* label */ \
40 " .if " __stringify(cb) " == 0\n" \
41 " .word 663f - .\n" /* new instruction */ \
42 " .else\n" \
43 " .word " __stringify(cb) "- .\n" /* callback */ \
44 " .endif\n" \
45 " .hword " __stringify(feature) "\n" /* feature bit */ \
46 " .byte 662b-661b\n" /* source len */ \
47 " .byte 664f-663f\n" /* replacement len */
48
49 /*
50 * alternative assembly primitive:
51 *
52 * If any of these .org directive fail, it means that insn1 and insn2
53 * don't have the same length. This used to be written as
54 *
55 * .if ((664b-663b) != (662b-661b))
56 * .error "Alternatives instruction length mismatch"
57 * .endif
58 *
59 * but most assemblers die if insn1 or insn2 have a .inst. This should
60 * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
61 * containing commit 4e4d08cf7399b606 or c1baaddf8861).
62 *
63 * Alternatives with callbacks do not generate replacement instructions.
64 */
65 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb) \
66 ".if "__stringify(cfg_enabled)" == 1\n" \
67 "661:\n\t" \
68 oldinstr "\n" \
69 "662:\n" \
70 ".pushsection .altinstructions,\"a\"\n" \
71 ALTINSTR_ENTRY(feature,cb) \
72 ".popsection\n" \
73 " .if " __stringify(cb) " == 0\n" \
74 ".pushsection .altinstr_replacement, \"a\"\n" \
75 "663:\n\t" \
76 newinstr "\n" \
77 "664:\n\t" \
78 ".popsection\n\t" \
79 ".org . - (664b-663b) + (662b-661b)\n\t" \
80 ".org . - (662b-661b) + (664b-663b)\n" \
81 ".else\n\t" \
82 "663:\n\t" \
83 "664:\n\t" \
84 ".endif\n" \
85 ".endif\n"
86
87 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \
88 __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
89
90 #define ALTERNATIVE_CB(oldinstr, cb) \
91 __ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb)
92 #else
93
94 #include <asm/assembler.h>
95
96 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
97 .word \orig_offset - .
98 .word \alt_offset - .
99 .hword \feature
100 .byte \orig_len
101 .byte \alt_len
102 .endm
103
104 .macro alternative_insn insn1, insn2, cap, enable = 1
105 .if \enable
106 661: \insn1
107 662: .pushsection .altinstructions, "a"
108 altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
109 .popsection
110 .pushsection .altinstr_replacement, "ax"
111 663: \insn2
112 664: .popsection
113 .org . - (664b-663b) + (662b-661b)
114 .org . - (662b-661b) + (664b-663b)
115 .endif
116 .endm
117
118 /*
119 * Alternative sequences
120 *
121 * The code for the case where the capability is not present will be
122 * assembled and linked as normal. There are no restrictions on this
123 * code.
124 *
125 * The code for the case where the capability is present will be
126 * assembled into a special section to be used for dynamic patching.
127 * Code for that case must:
128 *
129 * 1. Be exactly the same length (in bytes) as the default code
130 * sequence.
131 *
132 * 2. Not contain a branch target that is used outside of the
133 * alternative sequence it is defined in (branches into an
134 * alternative sequence are not fixed up).
135 */
136
137 /*
138 * Begin an alternative code sequence.
139 */
140 .macro alternative_if_not cap
141 .set .Lasm_alt_mode, 0
142 .pushsection .altinstructions, "a"
143 altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
144 .popsection
145 661:
146 .endm
147
148 .macro alternative_if cap
149 .set .Lasm_alt_mode, 1
150 .pushsection .altinstructions, "a"
151 altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
152 .popsection
153 .pushsection .altinstr_replacement, "ax"
154 .align 2 /* So GAS knows label 661 is suitably aligned */
155 661:
156 .endm
157
158 .macro alternative_cb cb
159 .set .Lasm_alt_mode, 0
160 .pushsection .altinstructions, "a"
161 altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
162 .popsection
163 661:
164 .endm
165
166 /*
167 * Provide the other half of the alternative code sequence.
168 */
169 .macro alternative_else
170 662:
171 .if .Lasm_alt_mode==0
172 .pushsection .altinstr_replacement, "ax"
173 .else
174 .popsection
175 .endif
176 663:
177 .endm
178
179 /*
180 * Complete an alternative code sequence.
181 */
182 .macro alternative_endif
183 664:
184 .if .Lasm_alt_mode==0
185 .popsection
186 .endif
187 .org . - (664b-663b) + (662b-661b)
188 .org . - (662b-661b) + (664b-663b)
189 .endm
190
191 /*
192 * Callback-based alternative epilogue
193 */
194 .macro alternative_cb_end
195 662:
196 .endm
197
198 /*
199 * Provides a trivial alternative or default sequence consisting solely
200 * of NOPs. The number of NOPs is chosen automatically to match the
201 * previous case.
202 */
203 .macro alternative_else_nop_endif
204 alternative_else
205 nops (662b-661b) / AARCH64_INSN_SIZE
206 alternative_endif
207 .endm
208
209 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...) \
210 alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
211
212 .macro user_alt, label, oldinstr, newinstr, cond
213 9999: alternative_insn "\oldinstr", "\newinstr", \cond
214 _ASM_EXTABLE 9999b, \label
215 .endm
216
217 /*
218 * Generate the assembly for UAO alternatives with exception table entries.
219 * This is complicated as there is no post-increment or pair versions of the
220 * unprivileged instructions, and USER() only works for single instructions.
221 */
222 #ifdef CONFIG_ARM64_UAO
223 .macro uao_ldp l, reg1, reg2, addr, post_inc
224 alternative_if_not ARM64_HAS_UAO
225 8888: ldp \reg1, \reg2, [\addr], \post_inc;
226 8889: nop;
227 nop;
228 alternative_else
229 ldtr \reg1, [\addr];
230 ldtr \reg2, [\addr, #8];
231 add \addr, \addr, \post_inc;
232 alternative_endif
233
234 _asm_extable 8888b,\l;
235 _asm_extable 8889b,\l;
236 .endm
237
238 .macro uao_stp l, reg1, reg2, addr, post_inc
239 alternative_if_not ARM64_HAS_UAO
240 8888: stp \reg1, \reg2, [\addr], \post_inc;
241 8889: nop;
242 nop;
243 alternative_else
244 sttr \reg1, [\addr];
245 sttr \reg2, [\addr, #8];
246 add \addr, \addr, \post_inc;
247 alternative_endif
248
249 _asm_extable 8888b,\l;
250 _asm_extable 8889b,\l;
251 .endm
252
253 .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
254 alternative_if_not ARM64_HAS_UAO
255 8888: \inst \reg, [\addr], \post_inc;
256 nop;
257 alternative_else
258 \alt_inst \reg, [\addr];
259 add \addr, \addr, \post_inc;
260 alternative_endif
261
262 _asm_extable 8888b,\l;
263 .endm
264 #else
265 .macro uao_ldp l, reg1, reg2, addr, post_inc
266 USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
267 .endm
268 .macro uao_stp l, reg1, reg2, addr, post_inc
269 USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
270 .endm
271 .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
272 USER(\l, \inst \reg, [\addr], \post_inc)
273 .endm
274 #endif
275
276 #endif /* __ASSEMBLY__ */
277
278 /*
279 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
280 *
281 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
282 * N.B. If CONFIG_FOO is specified, but not selected, the whole block
283 * will be omitted, including oldinstr.
284 */
285 #define ALTERNATIVE(oldinstr, newinstr, ...) \
286 _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
287
288 #endif /* __ASM_ALTERNATIVE_H */
289
