arch/x86/include/asm/alternative.h

   1 #ifndef _ASM_X86_ALTERNATIVE_H
   2 #define _ASM_X86_ALTERNATIVE_H
   3
   4 #ifndef __ASSEMBLY__
   5
   6 #include <linux/types.h>
   7 #include <linux/stddef.h>
   8 #include <linux/stringify.h>
   9 #include <asm/asm.h>
  10
  11 /*
  12  * Alternative inline assembly for SMP.
  13  *
  14  * The LOCK_PREFIX macro defined here replaces the LOCK and
  15  * LOCK_PREFIX macros used everywhere in the source tree.
  16  *
  17  * SMP alternatives use the same data structures as the other
  18  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  19  * UP system running a SMP kernel.  The existing apply_alternatives()
  20  * works fine for patching a SMP kernel for UP.
  21  *
  22  * The SMP alternative tables can be kept after boot and contain both
  23  * UP and SMP versions of the instructions to allow switching back to
  24  * SMP at runtime, when hotplugging in a new CPU, which is especially
  25  * useful in virtualized environments.
  26  *
  27  * The very common lock prefix is handled as special case in a
  28  * separate table which is a pure address list without replacement ptr
  29  * and size information.  That keeps the table sizes small.
  30  */
  31
  32 #ifdef CONFIG_SMP
  33 #define LOCK_PREFIX_HERE \
  34                 ".pushsection .smp_locks,\"a\"\n"       \
  35                 ".balign 4\n"                           \
  36                 ".long 671f - .\n" /* offset */         \
  37                 ".popsection\n"                         \
  38                 "671:"
  39
  40 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  41
  42 #else /* ! CONFIG_SMP */
  43 #define LOCK_PREFIX_HERE ""
  44 #define LOCK_PREFIX ""
  45 #endif
  46
  47 struct alt_instr {
  48         s32 instr_offset;       /* original instruction */
  49         s32 repl_offset;        /* offset to replacement instruction */
  50         u16 cpuid;              /* cpuid bit set for replacement */
  51         u8  instrlen;           /* length of original instruction */
  52         u8  replacementlen;     /* length of new instruction */
  53         u8  padlen;             /* length of build-time padding */
  54 } __packed;
  55
  56 /*
  57  * Debug flag that can be tested to see whether alternative
  58  * instructions were patched in already:
  59  */
  60 extern int alternatives_patched;
  61
  62 extern void alternative_instructions(void);
  63 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  64
  65 struct module;
  66
  67 #ifdef CONFIG_SMP
  68 extern void alternatives_smp_module_add(struct module *mod, char *name,
  69                                         void *locks, void *locks_end,
  70                                         void *text, void *text_end);
  71 extern void alternatives_smp_module_del(struct module *mod);
  72 extern void alternatives_enable_smp(void);
  73 extern int alternatives_text_reserved(void *start, void *end);
  74 extern bool skip_smp_alternatives;
  75 #else
  76 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  77                                                void *locks, void *locks_end,
  78                                                void *text, void *text_end) {}
  79 static inline void alternatives_smp_module_del(struct module *mod) {}
  80 static inline void alternatives_enable_smp(void) {}
  81 static inline int alternatives_text_reserved(void *start, void *end)
  82 {
  83         return 0;
  84 }
  85 #endif  /* CONFIG_SMP */
  86
  87 #define b_replacement(num)      "664"#num
  88 #define e_replacement(num)      "665"#num
  89
  90 #define alt_end_marker          "663"
  91 #define alt_slen                "662b-661b"
  92 #define alt_pad_len             alt_end_marker"b-662b"
  93 #define alt_total_slen          alt_end_marker"b-661b"
  94 #define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
  95
  96 #define __OLDINSTR(oldinstr, num)                                       \
  97         "661:\n\t" oldinstr "\n662:\n"                                  \
  98         ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
  99                 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
 100
 101 #define OLDINSTR(oldinstr, num)                                         \
 102         __OLDINSTR(oldinstr, num)                                       \
 103         alt_end_marker ":\n"
 104
 105 /*
 106  * max without conditionals. Idea adapted from:
 107  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 108  *
 109  * The additional "-" is needed because gas works with s32s.
 110  */
 111 #define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") - (" b ")))))"
 112
 113 /*
 114  * Pad the second replacement alternative with additional NOPs if it is
 115  * additionally longer than the first replacement alternative.
 116  */
 117 #define OLDINSTR_2(oldinstr, num1, num2) \
 118         "661:\n\t" oldinstr "\n662:\n"                                                          \
 119         ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 120                 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 121         alt_end_marker ":\n"
 122
 123 #define ALTINSTR_ENTRY(feature, num)                                          \
 124         " .long 661b - .\n"                             /* label           */ \
 125         " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 126         " .word " __stringify(feature) "\n"             /* feature bit     */ \
 127         " .byte " alt_total_slen "\n"                   /* source len      */ \
 128         " .byte " alt_rlen(num) "\n"                    /* replacement len */ \
 129         " .byte " alt_pad_len "\n"                      /* pad len */
 130
 131 #define ALTINSTR_REPLACEMENT(newinstr, feature, num)    /* replacement */     \
 132         b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
 133
 134 /* alternative assembly primitive: */
 135 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 136         OLDINSTR(oldinstr, 1)                                           \
 137         ".pushsection .altinstructions,\"a\"\n"                         \
 138         ALTINSTR_ENTRY(feature, 1)                                      \
 139         ".popsection\n"                                                 \
 140         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 141         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 142         ".popsection"
 143
 144 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 145         OLDINSTR_2(oldinstr, 1, 2)                                      \
 146         ".pushsection .altinstructions,\"a\"\n"                         \
 147         ALTINSTR_ENTRY(feature1, 1)                                     \
 148         ALTINSTR_ENTRY(feature2, 2)                                     \
 149         ".popsection\n"                                                 \
 150         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 151         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 152         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 153         ".popsection"
 154
 155 /*
 156  * Alternative instructions for different CPU types or capabilities.
 157  *
 158  * This allows to use optimized instructions even on generic binary
 159  * kernels.
 160  *
 161  * length of oldinstr must be longer or equal the length of newinstr
 162  * It can be padded with nops as needed.
 163  *
 164  * For non barrier like inlines please define new variants
 165  * without volatile and memory clobber.
 166  */
 167 #define alternative(oldinstr, newinstr, feature)                        \
 168         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 169
 170 #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 171         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 172
 173 /*
 174  * Alternative inline assembly with input.
 175  *
 176  * Pecularities:
 177  * No memory clobber here.
 178  * Argument numbers start with 1.
 179  * Best is to use constraints that are fixed size (like (%1) ... "r")
 180  * If you use variable sized constraints like "m" or "g" in the
 181  * replacement make sure to pad to the worst case length.
 182  * Leaving an unused argument 0 to keep API compatibility.
 183  */
 184 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 185         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 186                 : : "i" (0), ## input)
 187
 188 /*
 189  * This is similar to alternative_input. But it has two features and
 190  * respective instructions.
 191  *
 192  * If CPU has feature2, newinstr2 is used.
 193  * Otherwise, if CPU has feature1, newinstr1 is used.
 194  * Otherwise, oldinstr is used.
 195  */
 196 #define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 197                            feature2, input...)                               \
 198         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,            \
 199                 newinstr2, feature2)                                         \
 200                 : : "i" (0), ## input)
 201
 202 /* Like alternative_input, but with a single output argument */
 203 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 204         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 205                 : output : "i" (0), ## input)
 206
 207 /* Like alternative_io, but for replacing a direct call with another one. */
 208 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 209         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 210                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 211
 212 /*
 213  * Like alternative_call, but there are two features and respective functions.
 214  * If CPU has feature2, function2 is used.
 215  * Otherwise, if CPU has feature1, function1 is used.
 216  * Otherwise, old function is used.
 217  */
 218 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 219                            output, input...)                                  \
 220 {                                                                             \
 221         asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 222                 "call %P[new2]", feature2)                                    \
 223                 : output, ASM_CALL_CONSTRAINT                                 \
 224                 : [old] "i" (oldfunc), [new1] "i" (newfunc1),                 \
 225                   [new2] "i" (newfunc2), ## input);                           \
 226 }
 227
 228 /*
 229  * use this macro(s) if you need more than one output parameter
 230  * in alternative_io
 231  */
 232 #define ASM_OUTPUT2(a...) a
 233
 234 /*
 235  * use this macro if you need clobbers but no inputs in
 236  * alternative_{input,io,call}()
 237  */
 238 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 239
 240 #endif /* __ASSEMBLY__ */
 241
 242 #endif /* _ASM_X86_ALTERNATIVE_H */