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 <linux/const.h>
   6 #include <vdso/bits.h>
   7
   8 #include <asm/cpucaps.h>
   9 #include <asm/insn-def.h>
  10
  11 /*
  12  * Binutils 2.27.0 can't handle a 'UL' suffix on constants, so for the assembly
  13  * macros below we must use we must use `(1 << ARM64_CB_SHIFT)`.
  14  */
  15 #define ARM64_CB_SHIFT  15
  16 #define ARM64_CB_BIT    BIT(ARM64_CB_SHIFT)
  17
  18 #if ARM64_NCAPS >= ARM64_CB_BIT
  19 #error "cpucaps have overflown ARM64_CB_BIT"
  20 #endif
  21
  22 #ifndef __ASSEMBLY__
  23
  24 #include <linux/stringify.h>
  25
  26 #define ALTINSTR_ENTRY(cpucap)                                                \
  27         " .word 661b - .\n"                             /* label           */ \
  28         " .word 663f - .\n"                             /* new instruction */ \
  29         " .hword " __stringify(cpucap) "\n"             /* cpucap          */ \
  30         " .byte 662b-661b\n"                            /* source len      */ \
  31         " .byte 664f-663f\n"                            /* replacement len */
  32
  33 #define ALTINSTR_ENTRY_CB(cpucap, cb)                                         \
  34         " .word 661b - .\n"                             /* label           */ \
  35         " .word " __stringify(cb) "- .\n"               /* callback        */ \
  36         " .hword " __stringify(cpucap) "\n"             /* cpucap          */ \
  37         " .byte 662b-661b\n"                            /* source len      */ \
  38         " .byte 664f-663f\n"                            /* replacement len */
  39
  40 /*
  41  * alternative assembly primitive:
  42  *
  43  * If any of these .org directive fail, it means that insn1 and insn2
  44  * don't have the same length. This used to be written as
  45  *
  46  * .if ((664b-663b) != (662b-661b))
  47  *      .error "Alternatives instruction length mismatch"
  48  * .endif
  49  *
  50  * but most assemblers die if insn1 or insn2 have a .inst. This should
  51  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
  52  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
  53  *
  54  * Alternatives with callbacks do not generate replacement instructions.
  55  */
  56 #define __ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, cfg_enabled)      \
  57         ".if "__stringify(cfg_enabled)" == 1\n"                         \
  58         "661:\n\t"                                                      \
  59         oldinstr "\n"                                                   \
  60         "662:\n"                                                        \
  61         ".pushsection .altinstructions,\"a\"\n"                         \
  62         ALTINSTR_ENTRY(cpucap)                                          \
  63         ".popsection\n"                                                 \
  64         ".subsection 1\n"                                               \
  65         "663:\n\t"                                                      \
  66         newinstr "\n"                                                   \
  67         "664:\n\t"                                                      \
  68         ".org   . - (664b-663b) + (662b-661b)\n\t"                      \
  69         ".org   . - (662b-661b) + (664b-663b)\n\t"                      \
  70         ".previous\n"                                                   \
  71         ".endif\n"
  72
  73 #define __ALTERNATIVE_CFG_CB(oldinstr, cpucap, cfg_enabled, cb) \
  74         ".if "__stringify(cfg_enabled)" == 1\n"                         \
  75         "661:\n\t"                                                      \
  76         oldinstr "\n"                                                   \
  77         "662:\n"                                                        \
  78         ".pushsection .altinstructions,\"a\"\n"                         \
  79         ALTINSTR_ENTRY_CB(cpucap, cb)                                   \
  80         ".popsection\n"                                                 \
  81         "663:\n\t"                                                      \
  82         "664:\n\t"                                                      \
  83         ".endif\n"
  84
  85 #define _ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, cfg, ...)  \
  86         __ALTERNATIVE_CFG(oldinstr, newinstr, cpucap, IS_ENABLED(cfg))
  87
  88 #define ALTERNATIVE_CB(oldinstr, cpucap, cb) \
  89         __ALTERNATIVE_CFG_CB(oldinstr, (1 << ARM64_CB_SHIFT) | (cpucap), 1, cb)
  90 #else
  91
  92 #include <asm/assembler.h>
  93
  94 .macro altinstruction_entry orig_offset alt_offset cpucap orig_len alt_len
  95         .word \orig_offset - .
  96         .word \alt_offset - .
  97         .hword (\cpucap)
  98         .byte \orig_len
  99         .byte \alt_len
 100 .endm
 101
 102 .macro alternative_insn insn1, insn2, cap, enable = 1
 103         .if \enable
 104 661:    \insn1
 105 662:    .pushsection .altinstructions, "a"
 106         altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
 107         .popsection
 108         .subsection 1
 109 663:    \insn2
 110 664:    .org    . - (664b-663b) + (662b-661b)
 111         .org    . - (662b-661b) + (664b-663b)
 112         .previous
 113         .endif
 114 .endm
 115
 116 /*
 117  * Alternative sequences
 118  *
 119  * The code for the case where the capability is not present will be
 120  * assembled and linked as normal. There are no restrictions on this
 121  * code.
 122  *
 123  * The code for the case where the capability is present will be
 124  * assembled into a special section to be used for dynamic patching.
 125  * Code for that case must:
 126  *
 127  * 1. Be exactly the same length (in bytes) as the default code
 128  *    sequence.
 129  *
 130  * 2. Not contain a branch target that is used outside of the
 131  *    alternative sequence it is defined in (branches into an
 132  *    alternative sequence are not fixed up).
 133  */
 134
 135 /*
 136  * Begin an alternative code sequence.
 137  */
 138 .macro alternative_if_not cap
 139         .set .Lasm_alt_mode, 0
 140         .pushsection .altinstructions, "a"
 141         altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
 142         .popsection
 143 661:
 144 .endm
 145
 146 .macro alternative_if cap
 147         .set .Lasm_alt_mode, 1
 148         .pushsection .altinstructions, "a"
 149         altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
 150         .popsection
 151         .subsection 1
 152         .align 2        /* So GAS knows label 661 is suitably aligned */
 153 661:
 154 .endm
 155
 156 .macro alternative_cb cap, cb
 157         .set .Lasm_alt_mode, 0
 158         .pushsection .altinstructions, "a"
 159         altinstruction_entry 661f, \cb, (1 << ARM64_CB_SHIFT) | \cap, 662f-661f, 0
 160         .popsection
 161 661:
 162 .endm
 163
 164 /*
 165  * Provide the other half of the alternative code sequence.
 166  */
 167 .macro alternative_else
 168 662:
 169         .if .Lasm_alt_mode==0
 170         .subsection 1
 171         .else
 172         .previous
 173         .endif
 174 663:
 175 .endm
 176
 177 /*
 178  * Complete an alternative code sequence.
 179  */
 180 .macro alternative_endif
 181 664:
 182         .org    . - (664b-663b) + (662b-661b)
 183         .org    . - (662b-661b) + (664b-663b)
 184         .if .Lasm_alt_mode==0
 185         .previous
 186         .endif
 187 .endm
 188
 189 /*
 190  * Callback-based alternative epilogue
 191  */
 192 .macro alternative_cb_end
 193 662:
 194 .endm
 195
 196 /*
 197  * Provides a trivial alternative or default sequence consisting solely
 198  * of NOPs. The number of NOPs is chosen automatically to match the
 199  * previous case.
 200  */
 201 .macro alternative_else_nop_endif
 202 alternative_else
 203         nops    (662b-661b) / AARCH64_INSN_SIZE
 204 alternative_endif
 205 .endm
 206
 207 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)   \
 208         alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
 209
 210 #endif  /*  __ASSEMBLY__  */
 211
 212 /*
 213  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, cpucap));
 214  *
 215  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, cpucap, CONFIG_FOO));
 216  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
 217  *      will be omitted, including oldinstr.
 218  */
 219 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
 220         _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
 221
 222 #ifndef __ASSEMBLY__
 223
 224 #include <linux/types.h>
 225
 226 static __always_inline bool
 227 alternative_has_cap_likely(const unsigned long cpucap)
 228 {
 229         if (!cpucap_is_possible(cpucap))
 230                 return false;
 231
 232         asm goto(
 233 #ifdef BUILD_VDSO
 234         ALTERNATIVE("b  %l[l_no]", "nop", %[cpucap])
 235 #else
 236         ALTERNATIVE_CB("b       %l[l_no]", %[cpucap], alt_cb_patch_nops)
 237 #endif
 238         :
 239         : [cpucap] "i" (cpucap)
 240         :
 241         : l_no);
 242
 243         return true;
 244 l_no:
 245         return false;
 246 }
 247
 248 static __always_inline bool
 249 alternative_has_cap_unlikely(const unsigned long cpucap)
 250 {
 251         if (!cpucap_is_possible(cpucap))
 252                 return false;
 253
 254         asm goto(
 255         ALTERNATIVE("nop", "b   %l[l_yes]", %[cpucap])
 256         :
 257         : [cpucap] "i" (cpucap)
 258         :
 259         : l_yes);
 260
 261         return false;
 262 l_yes:
 263         return true;
 264 }
 265
 266 #endif /* __ASSEMBLY__ */
 267
 268 #endif /* __ASM_ALTERNATIVE_MACROS_H */