alternative.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef _ASM_ALTERNATIVE_H
  3#define _ASM_ALTERNATIVE_H
  4
  5#ifndef __ASSEMBLER__
  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 /* __ASSEMBLER__ */
110
111#endif /* _ASM_ALTERNATIVE_H */