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