arch/arm/include/asm/current.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Copyright (c) 2021 Keith Packard <[email protected]>
   4  * Copyright (c) 2021 Google, LLC <[email protected]>
   5  */
   6
   7 #ifndef _ASM_ARM_CURRENT_H
   8 #define _ASM_ARM_CURRENT_H
   9
  10 #ifndef __ASSEMBLY__
  11 #include <asm/insn.h>
  12
  13 struct task_struct;
  14
  15 extern struct task_struct *__current;
  16
  17 static __always_inline __attribute_const__ struct task_struct *get_current(void)
  18 {
  19         struct task_struct *cur;
  20
  21 #if __has_builtin(__builtin_thread_pointer) && \
  22     defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) && \
  23     !(defined(CONFIG_THUMB2_KERNEL) && \
  24       defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 130001)
  25         /*
  26          * Use the __builtin helper when available - this results in better
  27          * code, especially when using GCC in combination with the per-task
  28          * stack protector, as the compiler will recognize that it needs to
  29          * load the TLS register only once in every function.
  30          *
  31          * Clang < 13.0.1 gets this wrong for Thumb2 builds:
  32          * https://github.com/ClangBuiltLinux/linux/issues/1485
  33          */
  34         cur = __builtin_thread_pointer();
  35 #elif defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
  36         asm("0: mrc p15, 0, %0, c13, c0, 3                      \n\t"
  37 #ifdef CONFIG_CPU_V6
  38             "1:                                                 \n\t"
  39             "   .subsection 1                                   \n\t"
  40 #if defined(CONFIG_ARM_HAS_GROUP_RELOCS) && \
  41     !(defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS))
  42             "2: " LOAD_SYM_ARMV6(%0, __current) "               \n\t"
  43             "   b       1b                                      \n\t"
  44 #else
  45             "2: ldr     %0, 3f                                  \n\t"
  46             "   ldr     %0, [%0]                                \n\t"
  47             "   b       1b                                      \n\t"
  48             "3: .long   __current                               \n\t"
  49 #endif
  50             "   .previous                                       \n\t"
  51             "   .pushsection \".alt.smp.init\", \"a\"           \n\t"
  52             "   .long   0b - .                                  \n\t"
  53             "   b       . + (2b - 0b)                           \n\t"
  54             "   .popsection                                     \n\t"
  55 #endif
  56             : "=r"(cur));
  57 #elif __LINUX_ARM_ARCH__>= 7 || \
  58       !defined(CONFIG_ARM_HAS_GROUP_RELOCS) || \
  59       (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS))
  60         cur = __current;
  61 #else
  62         asm(LOAD_SYM_ARMV6(%0, __current) : "=r"(cur));
  63 #endif
  64         return cur;
  65 }
  66
  67 #define current get_current()
  68
  69 #endif /* __ASSEMBLY__ */
  70
  71 #endif /* _ASM_ARM_CURRENT_H */