1#ifndef __ASM_ALTERNATIVE_H
2#define __ASM_ALTERNATIVE_H
3
4#ifndef __ASSEMBLY__
5
6#include <linux/init.h>
7#include <linux/kconfig.h>
8#include <linux/types.h>
9#include <linux/stddef.h>
10#include <linux/stringify.h>
11
12struct alt_instr {
13	s32 orig_offset;	/* offset to original instruction */
14	s32 alt_offset;		/* offset to replacement instruction */
15	u16 cpufeature;		/* cpufeature bit set for replacement */
16	u8  orig_len;		/* size of original instruction(s) */
17	u8  alt_len;		/* size of new instruction(s), <= orig_len */
18};
19
20void __init apply_alternatives_all(void);
21void apply_alternatives(void *start, size_t length);
22void free_alternatives_memory(void);
23
24#define ALTINSTR_ENTRY(feature)						      \
25	" .word 661b - .\n"				/* label           */ \
26	" .word 663f - .\n"				/* new instruction */ \
27	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
28	" .byte 662b-661b\n"				/* source len      */ \
29	" .byte 664f-663f\n"				/* replacement len */
30
31/*
32 * alternative assembly primitive:
33 *
34 * If any of these .org directive fail, it means that insn1 and insn2
35 * don't have the same length. This used to be written as
36 *
37 * .if ((664b-663b) != (662b-661b))
38 * 	.error "Alternatives instruction length mismatch"
39 * .endif
40 *
41 * but most assemblers die if insn1 or insn2 have a .inst. This should
42 * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
43 * containing commit 4e4d08cf7399b606 or c1baaddf8861).
44 */
45#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)	\
46	".if "__stringify(cfg_enabled)" == 1\n"				\
47	"661:\n\t"							\
48	oldinstr "\n"							\
49	"662:\n"							\
50	".pushsection .altinstructions,\"a\"\n"				\
51	ALTINSTR_ENTRY(feature)						\
52	".popsection\n"							\
53	".pushsection .altinstr_replacement, \"a\"\n"			\
54	"663:\n\t"							\
55	newinstr "\n"							\
56	"664:\n\t"							\
57	".popsection\n\t"						\
58	".org	. - (664b-663b) + (662b-661b)\n\t"			\
59	".org	. - (662b-661b) + (664b-663b)\n"			\
60	".endif\n"
61
62#define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)	\
63	__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
64
65#else
66
67.macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
68	.word \orig_offset - .
69	.word \alt_offset - .
70	.hword \feature
71	.byte \orig_len
72	.byte \alt_len
73.endm
74
75.macro alternative_insn insn1, insn2, cap, enable = 1
76	.if \enable
77661:	\insn1
78662:	.pushsection .altinstructions, "a"
79	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
80	.popsection
81	.pushsection .altinstr_replacement, "ax"
82663:	\insn2
83664:	.popsection
84	.org	. - (664b-663b) + (662b-661b)
85	.org	. - (662b-661b) + (664b-663b)
86	.endif
87.endm
88
89/*
90 * Begin an alternative code sequence.
91 *
92 * The code that follows this macro will be assembled and linked as
93 * normal. There are no restrictions on this code.
94 */
95.macro alternative_if_not cap, enable = 1
96	.if \enable
97	.pushsection .altinstructions, "a"
98	altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
99	.popsection
100661:
101	.endif
102.endm
103
104/*
105 * Provide the alternative code sequence.
106 *
107 * The code that follows this macro is assembled into a special
108 * section to be used for dynamic patching. Code that follows this
109 * macro must:
110 *
111 * 1. Be exactly the same length (in bytes) as the default code
112 *    sequence.
113 *
114 * 2. Not contain a branch target that is used outside of the
115 *    alternative sequence it is defined in (branches into an
116 *    alternative sequence are not fixed up).
117 */
118.macro alternative_else, enable = 1
119	.if \enable
120662:	.pushsection .altinstr_replacement, "ax"
121663:
122	.endif
123.endm
124
125/*
126 * Complete an alternative code sequence.
127 */
128.macro alternative_endif, enable = 1
129	.if \enable
130664:	.popsection
131	.org	. - (664b-663b) + (662b-661b)
132	.org	. - (662b-661b) + (664b-663b)
133	.endif
134.endm
135
136#define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\
137	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
138
139
140#endif  /*  __ASSEMBLY__  */
141
142/*
143 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
144 *
145 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
146 * N.B. If CONFIG_FOO is specified, but not selected, the whole block
147 *      will be omitted, including oldinstr.
148 */
149#define ALTERNATIVE(oldinstr, newinstr, ...)   \
150	_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
151
152#endif /* __ASM_ALTERNATIVE_H */
153