alternative.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __ASM_ALTERNATIVE_H
   3 #define __ASM_ALTERNATIVE_H
   4
   5 #include <asm/cpucaps.h>
   6 #include <asm/insn.h>
   7
   8 #define ARM64_CB_PATCH ARM64_NCAPS
   9
  10 #ifndef __ASSEMBLY__
  11
  12 #include <linux/init.h>
  13 #include <linux/types.h>
  14 #include <linux/stddef.h>
  15 #include <linux/stringify.h>
  16
  17 struct alt_instr {
  18         s32 orig_offset;        /* offset to original instruction */
  19         s32 alt_offset;         /* offset to replacement instruction */
  20         u16 cpufeature;         /* cpufeature bit set for replacement */
  21         u8  orig_len;           /* size of original instruction(s) */
  22         u8  alt_len;            /* size of new instruction(s), <= orig_len */
  23 };
  24
  25 typedef void (*alternative_cb_t)(struct alt_instr *alt,
  26                                  __le32 *origptr, __le32 *updptr, int nr_inst);
  27
  28 void __init apply_boot_alternatives(void);
  29 void __init apply_alternatives_all(void);
  30 bool alternative_is_applied(u16 cpufeature);
  31
  32 #ifdef CONFIG_MODULES
  33 void apply_alternatives_module(void *start, size_t length);
  34 #else
  35 static inline void apply_alternatives_module(void *start, size_t length) { }
  36 #endif
  37
  38 #define ALTINSTR_ENTRY(feature,cb)                                            \
  39         " .word 661b - .\n"                             /* label           */ \
  40         " .if " __stringify(cb) " == 0\n"                                     \
  41         " .word 663f - .\n"                             /* new instruction */ \
  42         " .else\n"                                                            \
  43         " .word " __stringify(cb) "- .\n"               /* callback */        \
  44         " .endif\n"                                                           \
  45         " .hword " __stringify(feature) "\n"            /* feature bit     */ \
  46         " .byte 662b-661b\n"                            /* source len      */ \
  47         " .byte 664f-663f\n"                            /* replacement len */
  48
  49 /*
  50  * alternative assembly primitive:
  51  *
  52  * If any of these .org directive fail, it means that insn1 and insn2
  53  * don't have the same length. This used to be written as
  54  *
  55  * .if ((664b-663b) != (662b-661b))
  56  *      .error "Alternatives instruction length mismatch"
  57  * .endif
  58  *
  59  * but most assemblers die if insn1 or insn2 have a .inst. This should
  60  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
  61  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
  62  *
  63  * Alternatives with callbacks do not generate replacement instructions.
  64  */
  65 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb) \
  66         ".if "__stringify(cfg_enabled)" == 1\n"                         \
  67         "661:\n\t"                                                      \
  68         oldinstr "\n"                                                   \
  69         "662:\n"                                                        \
  70         ".pushsection .altinstructions,\"a\"\n"                         \
  71         ALTINSTR_ENTRY(feature,cb)                                      \
  72         ".popsection\n"                                                 \
  73         " .if " __stringify(cb) " == 0\n"                               \
  74         ".pushsection .altinstr_replacement, \"a\"\n"                   \
  75         "663:\n\t"                                                      \
  76         newinstr "\n"                                                   \
  77         "664:\n\t"                                                      \
  78         ".popsection\n\t"                                               \
  79         ".org   . - (664b-663b) + (662b-661b)\n\t"                      \
  80         ".org   . - (662b-661b) + (664b-663b)\n"                        \
  81         ".else\n\t"                                                     \
  82         "663:\n\t"                                                      \
  83         "664:\n\t"                                                      \
  84         ".endif\n"                                                      \
  85         ".endif\n"
  86
  87 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \
  88         __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
  89
  90 #define ALTERNATIVE_CB(oldinstr, cb) \
  91         __ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb)
  92 #else
  93
  94 #include <asm/assembler.h>
  95
  96 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
  97         .word \orig_offset - .
  98         .word \alt_offset - .
  99         .hword \feature
 100         .byte \orig_len
 101         .byte \alt_len
 102 .endm
 103
 104 .macro alternative_insn insn1, insn2, cap, enable = 1
 105         .if \enable
 106 661:    \insn1
 107 662:    .pushsection .altinstructions, "a"
 108         altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
 109         .popsection
 110         .pushsection .altinstr_replacement, "ax"
 111 663:    \insn2
 112 664:    .popsection
 113         .org    . - (664b-663b) + (662b-661b)
 114         .org    . - (662b-661b) + (664b-663b)
 115         .endif
 116 .endm
 117
 118 /*
 119  * Alternative sequences
 120  *
 121  * The code for the case where the capability is not present will be
 122  * assembled and linked as normal. There are no restrictions on this
 123  * code.
 124  *
 125  * The code for the case where the capability is present will be
 126  * assembled into a special section to be used for dynamic patching.
 127  * Code for that case must:
 128  *
 129  * 1. Be exactly the same length (in bytes) as the default code
 130  *    sequence.
 131  *
 132  * 2. Not contain a branch target that is used outside of the
 133  *    alternative sequence it is defined in (branches into an
 134  *    alternative sequence are not fixed up).
 135  */
 136
 137 /*
 138  * Begin an alternative code sequence.
 139  */
 140 .macro alternative_if_not cap
 141         .set .Lasm_alt_mode, 0
 142         .pushsection .altinstructions, "a"
 143         altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
 144         .popsection
 145 661:
 146 .endm
 147
 148 .macro alternative_if cap
 149         .set .Lasm_alt_mode, 1
 150         .pushsection .altinstructions, "a"
 151         altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
 152         .popsection
 153         .pushsection .altinstr_replacement, "ax"
 154         .align 2        /* So GAS knows label 661 is suitably aligned */
 155 661:
 156 .endm
 157
 158 .macro alternative_cb cb
 159         .set .Lasm_alt_mode, 0
 160         .pushsection .altinstructions, "a"
 161         altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
 162         .popsection
 163 661:
 164 .endm
 165
 166 /*
 167  * Provide the other half of the alternative code sequence.
 168  */
 169 .macro alternative_else
 170 662:
 171         .if .Lasm_alt_mode==0
 172         .pushsection .altinstr_replacement, "ax"
 173         .else
 174         .popsection
 175         .endif
 176 663:
 177 .endm
 178
 179 /*
 180  * Complete an alternative code sequence.
 181  */
 182 .macro alternative_endif
 183 664:
 184         .if .Lasm_alt_mode==0
 185         .popsection
 186         .endif
 187         .org    . - (664b-663b) + (662b-661b)
 188         .org    . - (662b-661b) + (664b-663b)
 189 .endm
 190
 191 /*
 192  * Callback-based alternative epilogue
 193  */
 194 .macro alternative_cb_end
 195 662:
 196 .endm
 197
 198 /*
 199  * Provides a trivial alternative or default sequence consisting solely
 200  * of NOPs. The number of NOPs is chosen automatically to match the
 201  * previous case.
 202  */
 203 .macro alternative_else_nop_endif
 204 alternative_else
 205         nops    (662b-661b) / AARCH64_INSN_SIZE
 206 alternative_endif
 207 .endm
 208
 209 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)   \
 210         alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
 211
 212 .macro user_alt, label, oldinstr, newinstr, cond
 213 9999:   alternative_insn "\oldinstr", "\newinstr", \cond
 214         _ASM_EXTABLE 9999b, \label
 215 .endm
 216
 217 /*
 218  * Generate the assembly for UAO alternatives with exception table entries.
 219  * This is complicated as there is no post-increment or pair versions of the
 220  * unprivileged instructions, and USER() only works for single instructions.
 221  */
 222 #ifdef CONFIG_ARM64_UAO
 223         .macro uao_ldp l, reg1, reg2, addr, post_inc
 224                 alternative_if_not ARM64_HAS_UAO
 225 8888:                   ldp     \reg1, \reg2, [\addr], \post_inc;
 226 8889:                   nop;
 227                         nop;
 228                 alternative_else
 229                         ldtr    \reg1, [\addr];
 230                         ldtr    \reg2, [\addr, #8];
 231                         add     \addr, \addr, \post_inc;
 232                 alternative_endif
 233
 234                 _asm_extable    8888b,\l;
 235                 _asm_extable    8889b,\l;
 236         .endm
 237
 238         .macro uao_stp l, reg1, reg2, addr, post_inc
 239                 alternative_if_not ARM64_HAS_UAO
 240 8888:                   stp     \reg1, \reg2, [\addr], \post_inc;
 241 8889:                   nop;
 242                         nop;
 243                 alternative_else
 244                         sttr    \reg1, [\addr];
 245                         sttr    \reg2, [\addr, #8];
 246                         add     \addr, \addr, \post_inc;
 247                 alternative_endif
 248
 249                 _asm_extable    8888b,\l;
 250                 _asm_extable    8889b,\l;
 251         .endm
 252
 253         .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
 254                 alternative_if_not ARM64_HAS_UAO
 255 8888:                   \inst   \reg, [\addr], \post_inc;
 256                         nop;
 257                 alternative_else
 258                         \alt_inst       \reg, [\addr];
 259                         add             \addr, \addr, \post_inc;
 260                 alternative_endif
 261
 262                 _asm_extable    8888b,\l;
 263         .endm
 264 #else
 265         .macro uao_ldp l, reg1, reg2, addr, post_inc
 266                 USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
 267         .endm
 268         .macro uao_stp l, reg1, reg2, addr, post_inc
 269                 USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
 270         .endm
 271         .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
 272                 USER(\l, \inst \reg, [\addr], \post_inc)
 273         .endm
 274 #endif
 275
 276 #endif  /*  __ASSEMBLY__  */
 277
 278 /*
 279  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
 280  *
 281  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
 282  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
 283  *      will be omitted, including oldinstr.
 284  */
 285 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
 286         _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
 287
 288 #endif /* __ASM_ALTERNATIVE_H */