arch/arm64/include/asm/alternative.h

   1 #ifndef __ASM_ALTERNATIVE_H
   2 #define __ASM_ALTERNATIVE_H
   3
   4 #include <asm/cpufeature.h>
   5
   6 #ifndef __ASSEMBLY__
   7
   8 #include <linux/init.h>
   9 #include <linux/kconfig.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  * Begin an alternative code sequence.
  94  *
  95  * The code that follows this macro will be assembled and linked as
  96  * normal. There are no restrictions on this code.
  97  */
  98 .macro alternative_if_not cap, enable = 1
  99         .if \enable
 100         .pushsection .altinstructions, "a"
 101         altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
 102         .popsection
 103 661:
 104         .endif
 105 .endm
 106
 107 /*
 108  * Provide the alternative code sequence.
 109  *
 110  * The code that follows this macro is assembled into a special
 111  * section to be used for dynamic patching. Code that follows this
 112  * macro must:
 113  *
 114  * 1. Be exactly the same length (in bytes) as the default code
 115  *    sequence.
 116  *
 117  * 2. Not contain a branch target that is used outside of the
 118  *    alternative sequence it is defined in (branches into an
 119  *    alternative sequence are not fixed up).
 120  */
 121 .macro alternative_else, enable = 1
 122         .if \enable
 123 662:    .pushsection .altinstr_replacement, "ax"
 124 663:
 125         .endif
 126 .endm
 127
 128 /*
 129  * Complete an alternative code sequence.
 130  */
 131 .macro alternative_endif, enable = 1
 132         .if \enable
 133 664:    .popsection
 134         .org    . - (664b-663b) + (662b-661b)
 135         .org    . - (662b-661b) + (664b-663b)
 136         .endif
 137 .endm
 138
 139 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)   \
 140         alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
 141
 142
 143 /*
 144  * Generate the assembly for UAO alternatives with exception table entries.
 145  * This is complicated as there is no post-increment or pair versions of the
 146  * unprivileged instructions, and USER() only works for single instructions.
 147  */
 148 #ifdef CONFIG_ARM64_UAO
 149         .macro uao_ldp l, reg1, reg2, addr, post_inc
 150                 alternative_if_not ARM64_HAS_UAO
 151 8888:                   ldp     \reg1, \reg2, [\addr], \post_inc;
 152 8889:                   nop;
 153                         nop;
 154                 alternative_else
 155                         ldtr    \reg1, [\addr];
 156                         ldtr    \reg2, [\addr, #8];
 157                         add     \addr, \addr, \post_inc;
 158                 alternative_endif
 159
 160                 _asm_extable    8888b,\l;
 161                 _asm_extable    8889b,\l;
 162         .endm
 163
 164         .macro uao_stp l, reg1, reg2, addr, post_inc
 165                 alternative_if_not ARM64_HAS_UAO
 166 8888:                   stp     \reg1, \reg2, [\addr], \post_inc;
 167 8889:                   nop;
 168                         nop;
 169                 alternative_else
 170                         sttr    \reg1, [\addr];
 171                         sttr    \reg2, [\addr, #8];
 172                         add     \addr, \addr, \post_inc;
 173                 alternative_endif
 174
 175                 _asm_extable    8888b,\l;
 176                 _asm_extable    8889b,\l;
 177         .endm
 178
 179         .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
 180                 alternative_if_not ARM64_HAS_UAO
 181 8888:                   \inst   \reg, [\addr], \post_inc;
 182                         nop;
 183                 alternative_else
 184                         \alt_inst       \reg, [\addr];
 185                         add             \addr, \addr, \post_inc;
 186                 alternative_endif
 187
 188                 _asm_extable    8888b,\l;
 189         .endm
 190 #else
 191         .macro uao_ldp l, reg1, reg2, addr, post_inc
 192                 USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
 193         .endm
 194         .macro uao_stp l, reg1, reg2, addr, post_inc
 195                 USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
 196         .endm
 197         .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
 198                 USER(\l, \inst \reg, [\addr], \post_inc)
 199         .endm
 200 #endif
 201
 202 #endif  /*  __ASSEMBLY__  */
 203
 204 /*
 205  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
 206  *
 207  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
 208  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
 209  *      will be omitted, including oldinstr.
 210  */
 211 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
 212         _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
 213
 214 #endif /* __ASM_ALTERNATIVE_H */