arch/arc/include/asm/jump_label.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_ARC_JUMP_LABEL_H
   3 #define _ASM_ARC_JUMP_LABEL_H
   4
   5 #ifndef __ASSEMBLY__
   6
   7 #include <linux/stringify.h>
   8 #include <linux/types.h>
   9
  10 #define JUMP_LABEL_NOP_SIZE 4
  11
  12 /*
  13  * NOTE about '.balign 4':
  14  *
  15  * To make atomic update of patched instruction available we need to guarantee
  16  * that this instruction doesn't cross L1 cache line boundary.
  17  *
  18  * As of today we simply align instruction which can be patched by 4 byte using
  19  * ".balign 4" directive. In that case patched instruction is aligned with one
  20  * 16-bit NOP_S if this is required.
  21  * However 'align by 4' directive is much stricter than it actually required.
  22  * It's enough that our 32-bit instruction don't cross L1 cache line boundary /
  23  * L1 I$ fetch block boundary which can be achieved by using
  24  * ".bundle_align_mode" assembler directive. That will save us from adding
  25  * useless NOP_S padding in most of the cases.
  26  *
  27  * TODO: switch to ".bundle_align_mode" directive using whin it will be
  28  * supported by ARC toolchain.
  29  */
  30
  31 static __always_inline bool arch_static_branch(struct static_key *key,
  32                                                bool branch)
  33 {
  34         asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)"   \n"
  35                  "1:                                                    \n"
  36                  "nop                                                   \n"
  37                  ".pushsection __jump_table, \"aw\"                     \n"
  38                  ".word 1b, %l[l_yes], %c0                              \n"
  39                  ".popsection                                           \n"
  40                  : : "i" (&((char *)key)[branch]) : : l_yes);
  41
  42         return false;
  43 l_yes:
  44         return true;
  45 }
  46
  47 static __always_inline bool arch_static_branch_jump(struct static_key *key,
  48                                                     bool branch)
  49 {
  50         asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)"   \n"
  51                  "1:                                                    \n"
  52                  "b %l[l_yes]                                           \n"
  53                  ".pushsection __jump_table, \"aw\"                     \n"
  54                  ".word 1b, %l[l_yes], %c0                              \n"
  55                  ".popsection                                           \n"
  56                  : : "i" (&((char *)key)[branch]) : : l_yes);
  57
  58         return false;
  59 l_yes:
  60         return true;
  61 }
  62
  63 typedef u32 jump_label_t;
  64
  65 struct jump_entry {
  66         jump_label_t code;
  67         jump_label_t target;
  68         jump_label_t key;
  69 };
  70
  71 #endif  /* __ASSEMBLY__ */
  72 #endif