arch/x86/include/asm/alternative-asm.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_X86_ALTERNATIVE_ASM_H
   3 #define _ASM_X86_ALTERNATIVE_ASM_H
   4
   5 #ifdef __ASSEMBLY__
   6
   7 #include <asm/asm.h>
   8
   9 #ifdef CONFIG_SMP
  10         .macro LOCK_PREFIX
  11 672:    lock
  12         .pushsection .smp_locks,"a"
  13         .balign 4
  14         .long 672b - .
  15         .popsection
  16         .endm
  17 #else
  18         .macro LOCK_PREFIX
  19         .endm
  20 #endif
  21
  22 /*
  23  * Issue one struct alt_instr descriptor entry (need to put it into
  24  * the section .altinstructions, see below). This entry contains
  25  * enough information for the alternatives patching code to patch an
  26  * instruction. See apply_alternatives().
  27  */
  28 .macro altinstruction_entry orig alt feature orig_len alt_len pad_len
  29         .long \orig - .
  30         .long \alt - .
  31         .word \feature
  32         .byte \orig_len
  33         .byte \alt_len
  34         .byte \pad_len
  35 .endm
  36
  37 /*
  38  * Define an alternative between two instructions. If @feature is
  39  * present, early code in apply_alternatives() replaces @oldinstr with
  40  * @newinstr. ".skip" directive takes care of proper instruction padding
  41  * in case @newinstr is longer than @oldinstr.
  42  */
  43 .macro ALTERNATIVE oldinstr, newinstr, feature
  44 140:
  45         \oldinstr
  46 141:
  47         .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
  48 142:
  49
  50         .pushsection .altinstructions,"a"
  51         altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f,142b-141b
  52         .popsection
  53
  54         .pushsection .altinstr_replacement,"ax"
  55 143:
  56         \newinstr
  57 144:
  58         .popsection
  59 .endm
  60
  61 #define old_len                 141b-140b
  62 #define new_len1                144f-143f
  63 #define new_len2                145f-144f
  64
  65 /*
  66  * gas compatible max based on the idea from:
  67  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
  68  *
  69  * The additional "-" is needed because gas uses a "true" value of -1.
  70  */
  71 #define alt_max_short(a, b)     ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
  72
  73
  74 /*
  75  * Same as ALTERNATIVE macro above but for two alternatives. If CPU
  76  * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
  77  * @feature2, it replaces @oldinstr with @feature2.
  78  */
  79 .macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
  80 140:
  81         \oldinstr
  82 141:
  83         .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
  84                 (alt_max_short(new_len1, new_len2) - (old_len)),0x90
  85 142:
  86
  87         .pushsection .altinstructions,"a"
  88         altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f,142b-141b
  89         altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f,142b-141b
  90         .popsection
  91
  92         .pushsection .altinstr_replacement,"ax"
  93 143:
  94         \newinstr1
  95 144:
  96         \newinstr2
  97 145:
  98         .popsection
  99 .endm
 100
 101 #endif  /*  __ASSEMBLY__  */
 102
 103 #endif /* _ASM_X86_ALTERNATIVE_ASM_H */