arch/arm64/include/asm/alternative-macros.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __ASM_ALTERNATIVE_MACROS_H
   3 #define __ASM_ALTERNATIVE_MACROS_H
   4
   5 #include <asm/cpucaps.h>
   6
   7 #define ARM64_CB_PATCH ARM64_NCAPS
   8
   9 /* A64 instructions are always 32 bits. */
  10 #define AARCH64_INSN_SIZE               4
  11
  12 #ifndef __ASSEMBLY__
  13
  14 #include <linux/stringify.h>
  15
  16 #define ALTINSTR_ENTRY(feature)                                               \
  17         " .word 661b - .\n"                             /* label           */ \
  18         " .word 663f - .\n"                             /* new instruction */ \
  19         " .hword " __stringify(feature) "\n"            /* feature bit     */ \
  20         " .byte 662b-661b\n"                            /* source len      */ \
  21         " .byte 664f-663f\n"                            /* replacement len */
  22
  23 #define ALTINSTR_ENTRY_CB(feature, cb)                                        \
  24         " .word 661b - .\n"                             /* label           */ \
  25         " .word " __stringify(cb) "- .\n"               /* callback */        \
  26         " .hword " __stringify(feature) "\n"            /* feature bit     */ \
  27         " .byte 662b-661b\n"                            /* source len      */ \
  28         " .byte 664f-663f\n"                            /* replacement len */
  29
  30 /*
  31  * alternative assembly primitive:
  32  *
  33  * If any of these .org directive fail, it means that insn1 and insn2
  34  * don't have the same length. This used to be written as
  35  *
  36  * .if ((664b-663b) != (662b-661b))
  37  *      .error "Alternatives instruction length mismatch"
  38  * .endif
  39  *
  40  * but most assemblers die if insn1 or insn2 have a .inst. This should
  41  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
  42  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
  43  *
  44  * Alternatives with callbacks do not generate replacement instructions.
  45  */
  46 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)     \
  47         ".if "__stringify(cfg_enabled)" == 1\n"                         \
  48         "661:\n\t"                                                      \
  49         oldinstr "\n"                                                   \
  50         "662:\n"                                                        \
  51         ".pushsection .altinstructions,\"a\"\n"                         \
  52         ALTINSTR_ENTRY(feature)                                         \
  53         ".popsection\n"                                                 \
  54         ".subsection 1\n"                                               \
  55         "663:\n\t"                                                      \
  56         newinstr "\n"                                                   \
  57         "664:\n\t"                                                      \
  58         ".org   . - (664b-663b) + (662b-661b)\n\t"                      \
  59         ".org   . - (662b-661b) + (664b-663b)\n\t"                      \
  60         ".previous\n"                                                   \
  61         ".endif\n"
  62
  63 #define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)        \
  64         ".if "__stringify(cfg_enabled)" == 1\n"                         \
  65         "661:\n\t"                                                      \
  66         oldinstr "\n"                                                   \
  67         "662:\n"                                                        \
  68         ".pushsection .altinstructions,\"a\"\n"                         \
  69         ALTINSTR_ENTRY_CB(feature, cb)                                  \
  70         ".popsection\n"                                                 \
  71         "663:\n\t"                                                      \
  72         "664:\n\t"                                                      \
  73         ".endif\n"
  74
  75 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \
  76         __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
  77
  78 #define ALTERNATIVE_CB(oldinstr, cb) \
  79         __ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb)
  80 #else
  81
  82 #include <asm/assembler.h>
  83
  84 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
  85         .word \orig_offset - .
  86         .word \alt_offset - .
  87         .hword \feature
  88         .byte \orig_len
  89         .byte \alt_len
  90 .endm
  91
  92 .macro alternative_insn insn1, insn2, cap, enable = 1
  93         .if \enable
  94 661:    \insn1
  95 662:    .pushsection .altinstructions, "a"
  96         altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
  97         .popsection
  98         .subsection 1
  99 663:    \insn2
 100 664:    .org    . - (664b-663b) + (662b-661b)
 101         .org    . - (662b-661b) + (664b-663b)
 102         .previous
 103         .endif
 104 .endm
 105
 106 /*
 107  * Alternative sequences
 108  *
 109  * The code for the case where the capability is not present will be
 110  * assembled and linked as normal. There are no restrictions on this
 111  * code.
 112  *
 113  * The code for the case where the capability is present will be
 114  * assembled into a special section to be used for dynamic patching.
 115  * Code for that case must:
 116  *
 117  * 1. Be exactly the same length (in bytes) as the default code
 118  *    sequence.
 119  *
 120  * 2. Not contain a branch target that is used outside of the
 121  *    alternative sequence it is defined in (branches into an
 122  *    alternative sequence are not fixed up).
 123  */
 124
 125 /*
 126  * Begin an alternative code sequence.
 127  */
 128 .macro alternative_if_not cap
 129         .set .Lasm_alt_mode, 0
 130         .pushsection .altinstructions, "a"
 131         altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
 132         .popsection
 133 661:
 134 .endm
 135
 136 .macro alternative_if cap
 137         .set .Lasm_alt_mode, 1
 138         .pushsection .altinstructions, "a"
 139         altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
 140         .popsection
 141         .subsection 1
 142         .align 2        /* So GAS knows label 661 is suitably aligned */
 143 661:
 144 .endm
 145
 146 .macro alternative_cb cb
 147         .set .Lasm_alt_mode, 0
 148         .pushsection .altinstructions, "a"
 149         altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
 150         .popsection
 151 661:
 152 .endm
 153
 154 /*
 155  * Provide the other half of the alternative code sequence.
 156  */
 157 .macro alternative_else
 158 662:
 159         .if .Lasm_alt_mode==0
 160         .subsection 1
 161         .else
 162         .previous
 163         .endif
 164 663:
 165 .endm
 166
 167 /*
 168  * Complete an alternative code sequence.
 169  */
 170 .macro alternative_endif
 171 664:
 172         .org    . - (664b-663b) + (662b-661b)
 173         .org    . - (662b-661b) + (664b-663b)
 174         .if .Lasm_alt_mode==0
 175         .previous
 176         .endif
 177 .endm
 178
 179 /*
 180  * Callback-based alternative epilogue
 181  */
 182 .macro alternative_cb_end
 183 662:
 184 .endm
 185
 186 /*
 187  * Provides a trivial alternative or default sequence consisting solely
 188  * of NOPs. The number of NOPs is chosen automatically to match the
 189  * previous case.
 190  */
 191 .macro alternative_else_nop_endif
 192 alternative_else
 193         nops    (662b-661b) / AARCH64_INSN_SIZE
 194 alternative_endif
 195 .endm
 196
 197 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)   \
 198         alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
 199
 200 .macro user_alt, label, oldinstr, newinstr, cond
 201 9999:   alternative_insn "\oldinstr", "\newinstr", \cond
 202         _asm_extable 9999b, \label
 203 .endm
 204
 205 #endif  /*  __ASSEMBLY__  */
 206
 207 /*
 208  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
 209  *
 210  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
 211  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
 212  *      will be omitted, including oldinstr.
 213  */
 214 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
 215         _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
 216
 217 #endif /* __ASM_ALTERNATIVE_MACROS_H */