linux/arch/xtensa/include/asm/jump_label.h
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   1/* SPDX-License-Identifier: GPL-2.0 */
   2/* Copyright (C) 2018 Cadence Design Systems Inc. */
   3
   4#ifndef _ASM_XTENSA_JUMP_LABEL_H
   5#define _ASM_XTENSA_JUMP_LABEL_H
   6
   7#ifndef __ASSEMBLY__
   8
   9#include <linux/types.h>
  10
  11#define JUMP_LABEL_NOP_SIZE 3
  12
  13static __always_inline bool arch_static_branch(struct static_key *key,
  14                                               bool branch)
  15{
  16        asm_volatile_goto("1:\n\t"
  17                          "_nop\n\t"
  18                          ".pushsection __jump_table,  \"aw\"\n\t"
  19                          ".word 1b, %l[l_yes], %c0\n\t"
  20                          ".popsection\n\t"
  21                          : :  "i" (&((char *)key)[branch]) :  : l_yes);
  22
  23        return false;
  24l_yes:
  25        return true;
  26}
  27
  28static __always_inline bool arch_static_branch_jump(struct static_key *key,
  29                                                    bool branch)
  30{
  31        /*
  32         * Xtensa assembler will mark certain points in the code
  33         * as unreachable, so that later assembler or linker relaxation
  34         * passes could use them. A spot right after the J instruction
  35         * is one such point. Assembler and/or linker may insert padding
  36         * or literals here, breaking code flow in case the J instruction
  37         * is later replaced with NOP. Put a label right after the J to
  38         * make it reachable and wrap both into a no-transform block
  39         * to avoid any assembler interference with this.
  40         */
  41        asm_volatile_goto("1:\n\t"
  42                          ".begin no-transform\n\t"
  43                          "_j %l[l_yes]\n\t"
  44                          "2:\n\t"
  45                          ".end no-transform\n\t"
  46                          ".pushsection __jump_table,  \"aw\"\n\t"
  47                          ".word 1b, %l[l_yes], %c0\n\t"
  48                          ".popsection\n\t"
  49                          : :  "i" (&((char *)key)[branch]) :  : l_yes);
  50
  51        return false;
  52l_yes:
  53        return true;
  54}
  55
  56typedef u32 jump_label_t;
  57
  58struct jump_entry {
  59        jump_label_t code;
  60        jump_label_t target;
  61        jump_label_t key;
  62};
  63
  64#endif  /* __ASSEMBLY__ */
  65#endif
  66