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

INCLUDED FROM

   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  * objtool annotation to ignore the alternatives and only consider the original
  24  * instruction(s).
  25  */
  26 .macro ANNOTATE_IGNORE_ALTERNATIVE
  27         .Lannotate_\@:
  28         .pushsection .discard.ignore_alts
  29         .long .Lannotate_\@ - .
  30         .popsection
  31 .endm
  32 
  33 /*
  34  * Issue one struct alt_instr descriptor entry (need to put it into
  35  * the section .altinstructions, see below). This entry contains
  36  * enough information for the alternatives patching code to patch an
  37  * instruction. See apply_alternatives().
  38  */
  39 .macro altinstruction_entry orig alt feature orig_len alt_len pad_len
  40         .long \orig - .
  41         .long \alt - .
  42         .word \feature
  43         .byte \orig_len
  44         .byte \alt_len
  45         .byte \pad_len
  46 .endm
  47 
  48 /*
  49  * Define an alternative between two instructions. If @feature is
  50  * present, early code in apply_alternatives() replaces @oldinstr with
  51  * @newinstr. ".skip" directive takes care of proper instruction padding
  52  * in case @newinstr is longer than @oldinstr.
  53  */
  54 .macro ALTERNATIVE oldinstr, newinstr, feature
  55 140:
  56         \oldinstr
  57 141:
  58         .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
  59 142:
  60 
  61         .pushsection .altinstructions,"a"
  62         altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f,142b-141b
  63         .popsection
  64 
  65         .pushsection .altinstr_replacement,"ax"
  66 143:
  67         \newinstr
  68 144:
  69         .popsection
  70 .endm
  71 
  72 #define old_len                 141b-140b
  73 #define new_len1                144f-143f
  74 #define new_len2                145f-144f
  75 
  76 /*
  77  * gas compatible max based on the idea from:
  78  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
  79  *
  80  * The additional "-" is needed because gas uses a "true" value of -1.
  81  */
  82 #define alt_max_short(a, b)     ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
  83 
  84 
  85 /*
  86  * Same as ALTERNATIVE macro above but for two alternatives. If CPU
  87  * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
  88  * @feature2, it replaces @oldinstr with @feature2.
  89  */
  90 .macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
  91 140:
  92         \oldinstr
  93 141:
  94         .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
  95                 (alt_max_short(new_len1, new_len2) - (old_len)),0x90
  96 142:
  97 
  98         .pushsection .altinstructions,"a"
  99         altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f,142b-141b
 100         altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f,142b-141b
 101         .popsection
 102 
 103         .pushsection .altinstr_replacement,"ax"
 104 143:
 105         \newinstr1
 106 144:
 107         \newinstr2
 108 145:
 109         .popsection
 110 .endm
 111 
 112 #endif  /*  __ASSEMBLY__  */
 113 
 114 #endif /* _ASM_X86_ALTERNATIVE_ASM_H */