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
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