include/asm-i386/alternative.h

   1 #ifndef _I386_ALTERNATIVE_H
   2 #define _I386_ALTERNATIVE_H
   3
   4 #ifdef __KERNEL__
   5
   6 struct alt_instr {
   7         u8 *instr;              /* original instruction */
   8         u8 *replacement;
   9         u8  cpuid;              /* cpuid bit set for replacement */
  10         u8  instrlen;           /* length of original instruction */
  11         u8  replacementlen;     /* length of new instruction, <= instrlen */
  12         u8  pad;
  13 };
  14
  15 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  16
  17 struct module;
  18 extern void alternatives_smp_module_add(struct module *mod, char *name,
  19                                         void *locks, void *locks_end,
  20                                         void *text, void *text_end);
  21 extern void alternatives_smp_module_del(struct module *mod);
  22 extern void alternatives_smp_switch(int smp);
  23
  24 #endif
  25
  26 /*
  27  * Alternative instructions for different CPU types or capabilities.
  28  *
  29  * This allows to use optimized instructions even on generic binary
  30  * kernels.
  31  *
  32  * length of oldinstr must be longer or equal the length of newinstr
  33  * It can be padded with nops as needed.
  34  *
  35  * For non barrier like inlines please define new variants
  36  * without volatile and memory clobber.
  37  */
  38 #define alternative(oldinstr, newinstr, feature)                        \
  39         asm volatile ("661:\n\t" oldinstr "\n662:\n"                    \
  40                       ".section .altinstructions,\"a\"\n"               \
  41                       "  .align 4\n"                                    \
  42                       "  .long 661b\n"            /* label */           \
  43                       "  .long 663f\n"            /* new instruction */ \
  44                       "  .byte %c0\n"             /* feature bit */     \
  45                       "  .byte 662b-661b\n"       /* sourcelen */       \
  46                       "  .byte 664f-663f\n"       /* replacementlen */  \
  47                       ".previous\n"                                     \
  48                       ".section .altinstr_replacement,\"ax\"\n"         \
  49                       "663:\n\t" newinstr "\n664:\n"   /* replacement */\
  50                       ".previous" :: "i" (feature) : "memory")
  51
  52 /*
  53  * Alternative inline assembly with input.
  54  *
  55  * Pecularities:
  56  * No memory clobber here.
  57  * Argument numbers start with 1.
  58  * Best is to use constraints that are fixed size (like (%1) ... "r")
  59  * If you use variable sized constraints like "m" or "g" in the
  60  * replacement maake sure to pad to the worst case length.
  61  */
  62 #define alternative_input(oldinstr, newinstr, feature, input...)        \
  63         asm volatile ("661:\n\t" oldinstr "\n662:\n"                    \
  64                       ".section .altinstructions,\"a\"\n"               \
  65                       "  .align 4\n"                                    \
  66                       "  .long 661b\n"            /* label */           \
  67                       "  .long 663f\n"            /* new instruction */ \
  68                       "  .byte %c0\n"             /* feature bit */     \
  69                       "  .byte 662b-661b\n"       /* sourcelen */       \
  70                       "  .byte 664f-663f\n"       /* replacementlen */  \
  71                       ".previous\n"                                     \
  72                       ".section .altinstr_replacement,\"ax\"\n"         \
  73                       "663:\n\t" newinstr "\n664:\n"   /* replacement */\
  74                       ".previous" :: "i" (feature), ##input)
  75
  76 /*
  77  * Alternative inline assembly for SMP.
  78  *
  79  * alternative_smp() takes two versions (SMP first, UP second) and is
  80  * for more complex stuff such as spinlocks.
  81  *
  82  * The LOCK_PREFIX macro defined here replaces the LOCK and
  83  * LOCK_PREFIX macros used everywhere in the source tree.
  84  *
  85  * SMP alternatives use the same data structures as the other
  86  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  87  * UP system running a SMP kernel.  The existing apply_alternatives()
  88  * works fine for patching a SMP kernel for UP.
  89  *
  90  * The SMP alternative tables can be kept after boot and contain both
  91  * UP and SMP versions of the instructions to allow switching back to
  92  * SMP at runtime, when hotplugging in a new CPU, which is especially
  93  * useful in virtualized environments.
  94  *
  95  * The very common lock prefix is handled as special case in a
  96  * separate table which is a pure address list without replacement ptr
  97  * and size information.  That keeps the table sizes small.
  98  */
  99
 100 #ifdef CONFIG_SMP
 101 #define alternative_smp(smpinstr, upinstr, args...)                     \
 102         asm volatile ("661:\n\t" smpinstr "\n662:\n"                    \
 103                       ".section .smp_altinstructions,\"a\"\n"           \
 104                       "  .align 4\n"                                    \
 105                       "  .long 661b\n"            /* label */           \
 106                       "  .long 663f\n"            /* new instruction */ \
 107                       "  .byte 0x68\n"            /* X86_FEATURE_UP */  \
 108                       "  .byte 662b-661b\n"       /* sourcelen */       \
 109                       "  .byte 664f-663f\n"       /* replacementlen */  \
 110                       ".previous\n"                                     \
 111                       ".section .smp_altinstr_replacement,\"awx\"\n"    \
 112                       "663:\n\t" upinstr "\n"     /* replacement */     \
 113                       "664:\n\t.fill 662b-661b,1,0x42\n" /* space for original */ \
 114                       ".previous" : args)
 115
 116 #define LOCK_PREFIX \
 117                 ".section .smp_locks,\"a\"\n"   \
 118                 "  .align 4\n"                  \
 119                 "  .long 661f\n" /* address */  \
 120                 ".previous\n"                   \
 121                 "661:\n\tlock; "
 122
 123 #else /* ! CONFIG_SMP */
 124 #define alternative_smp(smpinstr, upinstr, args...) \
 125         asm volatile (upinstr : args)
 126 #define LOCK_PREFIX ""
 127 #endif
 128
 129 #endif /* _I386_ALTERNATIVE_H */