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
12 struct 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 */
24 extern int alternatives_patched;
25 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
26
27 extern void alternative_instructions(void);
28 extern 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
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.