arch/x86/include/asm/static_call.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_STATIC_CALL_H
   3 #define _ASM_STATIC_CALL_H
   4
   5 #include <asm/text-patching.h>
   6
   7 /*
   8  * For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
   9  * uses the current value of the key->func pointer to do an indirect jump to
  10  * the function.  This trampoline is only used during boot, before the call
  11  * sites get patched by static_call_update().  The name of this trampoline has
  12  * a magical aspect: objtool uses it to find static call sites so it can create
  13  * the .static_call_sites section.
  14  *
  15  * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
  16  * does a direct jump to the function.  The direct jump gets patched by
  17  * static_call_update().
  18  *
  19  * Having the trampoline in a special section forces GCC to emit a JMP.d32 when
  20  * it does tail-call optimization on the call; since you cannot compute the
  21  * relative displacement across sections.
  22  */
  23
  24 #define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns)                    \
  25         asm(".pushsection .static_call.text, \"ax\"             \n"     \
  26             ".align 4                                           \n"     \
  27             ".globl " STATIC_CALL_TRAMP_STR(name) "             \n"     \
  28             STATIC_CALL_TRAMP_STR(name) ":                      \n"     \
  29             insns "                                             \n"     \
  30             ".type " STATIC_CALL_TRAMP_STR(name) ", @function   \n"     \
  31             ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
  32             ".popsection                                        \n")
  33
  34 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)                       \
  35         __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
  36
  37 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)                        \
  38         __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
  39
  40 #endif /* _ASM_STATIC_CALL_H */