1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_ALTERNATIVE_H
3#define _ASM_ALTERNATIVE_H
4
5#ifndef __ASSEMBLY__
6
7#include <linux/types.h>
8#include <linux/stddef.h>
9#include <linux/stringify.h>
10#include <asm/asm.h>
11
12struct alt_instr {
13	s32 instr_offset;	/* offset to original instruction */
14	s32 replace_offset;	/* offset to replacement instruction */
15	u16 feature;		/* feature bit set for replacement */
16	u8  instrlen;		/* length of original instruction */
17	u8  replacementlen;	/* length of new instruction */
18} __packed;
19
20/*
21 * Debug flag that can be tested to see whether alternative
22 * instructions were patched in already:
23 */
24extern int alternatives_patched;
25extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
26
27extern void alternative_instructions(void);
28extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
29
30#define b_replacement(num)	"664"#num
31#define e_replacement(num)	"665"#num
32
33#define alt_end_marker		"663"
34#define alt_slen		"662b-661b"
35#define alt_total_slen		alt_end_marker"b-661b"
36#define alt_rlen(num)		e_replacement(num)"f-"b_replacement(num)"f"
37
38#define __OLDINSTR(oldinstr, num)					\
39	"661:\n\t" oldinstr "\n662:\n"					\
40	".fill -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "		\
41		"((" alt_rlen(num) ")-(" alt_slen ")) / 4, 4, 0x03400000\n"
42
43#define OLDINSTR(oldinstr, num)						\
44	__OLDINSTR(oldinstr, num)					\
45	alt_end_marker ":\n"
46
47#define alt_max_short(a, b)	"((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
48
49/*
50 * Pad the second replacement alternative with additional NOPs if it is
51 * additionally longer than the first replacement alternative.
52 */
53#define OLDINSTR_2(oldinstr, num1, num2) \
54	"661:\n\t" oldinstr "\n662:\n"								\
55	".fill -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "	\
56		"(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) / 4, "	\
57		"4, 0x03400000\n"	\
58	alt_end_marker ":\n"
59
60#define ALTINSTR_ENTRY(feature, num)					      \
61	" .long 661b - .\n"				/* label           */ \
62	" .long " b_replacement(num)"f - .\n"		/* new instruction */ \
63	" .short " __stringify(feature) "\n"		/* feature bit     */ \
64	" .byte " alt_total_slen "\n"			/* source len      */ \
65	" .byte " alt_rlen(num) "\n"			/* replacement len */
66
67#define ALTINSTR_REPLACEMENT(newinstr, feature, num)	/* replacement */     \
68	b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
69
70/* alternative assembly primitive: */
71#define ALTERNATIVE(oldinstr, newinstr, feature)			\
72	OLDINSTR(oldinstr, 1)						\
73	".pushsection .altinstructions,\"a\"\n"				\
74	ALTINSTR_ENTRY(feature, 1)					\
75	".popsection\n"							\
76	".subsection 1\n" \
77	ALTINSTR_REPLACEMENT(newinstr, feature, 1)			\
78	".previous\n"
79
80#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
81	OLDINSTR_2(oldinstr, 1, 2)					\
82	".pushsection .altinstructions,\"a\"\n"				\
83	ALTINSTR_ENTRY(feature1, 1)					\
84	ALTINSTR_ENTRY(feature2, 2)					\
85	".popsection\n"							\
86	".subsection 1\n" \
87	ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)			\
88	ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)			\
89	".previous\n"
90
91/*
92 * Alternative instructions for different CPU types or capabilities.
93 *
94 * This allows to use optimized instructions even on generic binary
95 * kernels.
96 *
97 * length of oldinstr must be longer or equal the length of newinstr
98 * It can be padded with nops as needed.
99 *
100 * For non barrier like inlines please define new variants
101 * without volatile and memory clobber.
102 */
103#define alternative(oldinstr, newinstr, feature)			\
104	(asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory"))
105
106#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
107	(asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory"))
108
109#endif /* __ASSEMBLY__ */
110
111#endif /* _ASM_ALTERNATIVE_H */
112