arch/arm64/include/asm/alternative.h

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