xref: /linux/arch/arm64/include/asm/alternative-macros.h (revision a4eb44a6435d6d8f9e642407a4a06f65eb90ca04)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_ALTERNATIVE_MACROS_H
3 #define __ASM_ALTERNATIVE_MACROS_H
4 
5 #include <asm/cpucaps.h>
6 #include <asm/insn-def.h>
7 
8 #define ARM64_CB_PATCH ARM64_NCAPS
9 
10 #ifndef __ASSEMBLY__
11 
12 #include <linux/stringify.h>
13 
14 #define ALTINSTR_ENTRY(feature)					              \
15 	" .word 661b - .\n"				/* label           */ \
16 	" .word 663f - .\n"				/* new instruction */ \
17 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
18 	" .byte 662b-661b\n"				/* source len      */ \
19 	" .byte 664f-663f\n"				/* replacement len */
20 
21 #define ALTINSTR_ENTRY_CB(feature, cb)					      \
22 	" .word 661b - .\n"				/* label           */ \
23 	" .word " __stringify(cb) "- .\n"		/* callback */	      \
24 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
25 	" .byte 662b-661b\n"				/* source len      */ \
26 	" .byte 664f-663f\n"				/* replacement len */
27 
28 /*
29  * alternative assembly primitive:
30  *
31  * If any of these .org directive fail, it means that insn1 and insn2
32  * don't have the same length. This used to be written as
33  *
34  * .if ((664b-663b) != (662b-661b))
35  * 	.error "Alternatives instruction length mismatch"
36  * .endif
37  *
38  * but most assemblers die if insn1 or insn2 have a .inst. This should
39  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
40  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
41  *
42  * Alternatives with callbacks do not generate replacement instructions.
43  */
44 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)	\
45 	".if "__stringify(cfg_enabled)" == 1\n"				\
46 	"661:\n\t"							\
47 	oldinstr "\n"							\
48 	"662:\n"							\
49 	".pushsection .altinstructions,\"a\"\n"				\
50 	ALTINSTR_ENTRY(feature)						\
51 	".popsection\n"							\
52 	".subsection 1\n"						\
53 	"663:\n\t"							\
54 	newinstr "\n"							\
55 	"664:\n\t"							\
56 	".org	. - (664b-663b) + (662b-661b)\n\t"			\
57 	".org	. - (662b-661b) + (664b-663b)\n\t"			\
58 	".previous\n"							\
59 	".endif\n"
60 
61 #define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)	\
62 	".if "__stringify(cfg_enabled)" == 1\n"				\
63 	"661:\n\t"							\
64 	oldinstr "\n"							\
65 	"662:\n"							\
66 	".pushsection .altinstructions,\"a\"\n"				\
67 	ALTINSTR_ENTRY_CB(feature, cb)					\
68 	".popsection\n"							\
69 	"663:\n\t"							\
70 	"664:\n\t"							\
71 	".endif\n"
72 
73 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)	\
74 	__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
75 
76 #define ALTERNATIVE_CB(oldinstr, cb) \
77 	__ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb)
78 #else
79 
80 #include <asm/assembler.h>
81 
82 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
83 	.word \orig_offset - .
84 	.word \alt_offset - .
85 	.hword \feature
86 	.byte \orig_len
87 	.byte \alt_len
88 .endm
89 
90 .macro alternative_insn insn1, insn2, cap, enable = 1
91 	.if \enable
92 661:	\insn1
93 662:	.pushsection .altinstructions, "a"
94 	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
95 	.popsection
96 	.subsection 1
97 663:	\insn2
98 664:	.org	. - (664b-663b) + (662b-661b)
99 	.org	. - (662b-661b) + (664b-663b)
100 	.previous
101 	.endif
102 .endm
103 
104 /*
105  * Alternative sequences
106  *
107  * The code for the case where the capability is not present will be
108  * assembled and linked as normal. There are no restrictions on this
109  * code.
110  *
111  * The code for the case where the capability is present will be
112  * assembled into a special section to be used for dynamic patching.
113  * Code for that case must:
114  *
115  * 1. Be exactly the same length (in bytes) as the default code
116  *    sequence.
117  *
118  * 2. Not contain a branch target that is used outside of the
119  *    alternative sequence it is defined in (branches into an
120  *    alternative sequence are not fixed up).
121  */
122 
123 /*
124  * Begin an alternative code sequence.
125  */
126 .macro alternative_if_not cap
127 	.set .Lasm_alt_mode, 0
128 	.pushsection .altinstructions, "a"
129 	altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
130 	.popsection
131 661:
132 .endm
133 
134 .macro alternative_if cap
135 	.set .Lasm_alt_mode, 1
136 	.pushsection .altinstructions, "a"
137 	altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
138 	.popsection
139 	.subsection 1
140 	.align 2	/* So GAS knows label 661 is suitably aligned */
141 661:
142 .endm
143 
144 .macro alternative_cb cb
145 	.set .Lasm_alt_mode, 0
146 	.pushsection .altinstructions, "a"
147 	altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
148 	.popsection
149 661:
150 .endm
151 
152 /*
153  * Provide the other half of the alternative code sequence.
154  */
155 .macro alternative_else
156 662:
157 	.if .Lasm_alt_mode==0
158 	.subsection 1
159 	.else
160 	.previous
161 	.endif
162 663:
163 .endm
164 
165 /*
166  * Complete an alternative code sequence.
167  */
168 .macro alternative_endif
169 664:
170 	.org	. - (664b-663b) + (662b-661b)
171 	.org	. - (662b-661b) + (664b-663b)
172 	.if .Lasm_alt_mode==0
173 	.previous
174 	.endif
175 .endm
176 
177 /*
178  * Callback-based alternative epilogue
179  */
180 .macro alternative_cb_end
181 662:
182 .endm
183 
184 /*
185  * Provides a trivial alternative or default sequence consisting solely
186  * of NOPs. The number of NOPs is chosen automatically to match the
187  * previous case.
188  */
189 .macro alternative_else_nop_endif
190 alternative_else
191 	nops	(662b-661b) / AARCH64_INSN_SIZE
192 alternative_endif
193 .endm
194 
195 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\
196 	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
197 
198 #endif  /*  __ASSEMBLY__  */
199 
200 /*
201  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
202  *
203  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
204  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
205  *      will be omitted, including oldinstr.
206  */
207 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
208 	_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
209 
210 #endif /* __ASM_ALTERNATIVE_MACROS_H */
211