arch/arm64/include/asm/alternative.h

   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
  12 struct 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
  20 void __init apply_alternatives_all(void);
  21 void apply_alternatives(void *start, size_t length);
  22 void 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
  77 661:    \insn1
  78 662:    .pushsection .altinstructions, "a"
  79         altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
  80         .popsection
  81         .pushsection .altinstr_replacement, "ax"
  82 663:    \insn2
  83 664:    .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
 100 661:
 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
 120 662:    .pushsection .altinstr_replacement, "ax"
 121 663:
 122         .endif
 123 .endm
 124
 125 /*
 126  * Complete an alternative code sequence.
 127  */
 128 .macro alternative_endif, enable = 1
 129         .if \enable
 130 664:    .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 */