/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_ALTERNATIVE_H
#define _ASM_ALTERNATIVE_H

#ifndef __ASSEMBLER__

#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/stringify.h>
#include <asm/asm.h>

struct alt_instr {
        s32 instr_offset;       /* offset to original instruction */
        s32 replace_offset;     /* offset to replacement instruction */
        u16 feature;            /* feature bit set for replacement */
        u8  instrlen;           /* length of original instruction */
        u8  replacementlen;     /* length of new instruction */
} __packed;

/*
 * Debug flag that can be tested to see whether alternative
 * instructions were patched in already:
 */
extern int alternatives_patched;
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];

extern void alternative_instructions(void);
extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);

#define b_replacement(num)      "664"#num
#define e_replacement(num)      "665"#num

#define alt_end_marker          "663"
#define alt_slen                "662b-661b"
#define alt_total_slen          alt_end_marker"b-661b"
#define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"

#define __OLDINSTR(oldinstr, num)                                       \
        "661:\n\t" oldinstr "\n662:\n"                                  \
        ".fill -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
                "((" alt_rlen(num) ")-(" alt_slen ")) / 4, 4, 0x03400000\n"

#define OLDINSTR(oldinstr, num)                                         \
        __OLDINSTR(oldinstr, num)                                       \
        alt_end_marker ":\n"

#define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"

/*
 * Pad the second replacement alternative with additional NOPs if it is
 * additionally longer than the first replacement alternative.
 */
#define OLDINSTR_2(oldinstr, num1, num2) \
        "661:\n\t" oldinstr "\n662:\n"                                                          \
        ".fill -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
                "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) / 4, "    \
                "4, 0x03400000\n"       \
        alt_end_marker ":\n"

#define ALTINSTR_ENTRY(feature, num)                                          \
        " .long 661b - .\n"                             /* label           */ \
        " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
        " .short " __stringify(feature) "\n"            /* feature bit     */ \
        " .byte " alt_total_slen "\n"                   /* source len      */ \
        " .byte " alt_rlen(num) "\n"                    /* replacement len */

#define ALTINSTR_REPLACEMENT(newinstr, feature, num)    /* replacement */     \
        b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"

/* alternative assembly primitive: */
#define ALTERNATIVE(oldinstr, newinstr, feature)                        \
        OLDINSTR(oldinstr, 1)                                           \
        ".pushsection .altinstructions,\"a\"\n"                         \
        ALTINSTR_ENTRY(feature, 1)                                      \
        ".popsection\n"                                                 \
        ".subsection 1\n" \
        ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
        ".previous\n"

#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
        OLDINSTR_2(oldinstr, 1, 2)                                      \
        ".pushsection .altinstructions,\"a\"\n"                         \
        ALTINSTR_ENTRY(feature1, 1)                                     \
        ALTINSTR_ENTRY(feature2, 2)                                     \
        ".popsection\n"                                                 \
        ".subsection 1\n" \
        ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
        ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
        ".previous\n"

/*
 * Alternative instructions for different CPU types or capabilities.
 *
 * This allows to use optimized instructions even on generic binary
 * kernels.
 *
 * length of oldinstr must be longer or equal the length of newinstr
 * It can be padded with nops as needed.
 *
 * For non barrier like inlines please define new variants
 * without volatile and memory clobber.
 */
#define alternative(oldinstr, newinstr, feature)                        \
        (asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory"))

#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
        (asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory"))

#endif /* __ASSEMBLER__ */

#endif /* _ASM_ALTERNATIVE_H */