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 /*
  25  * The trampoline is 8 bytes and of the general form:
  26  *
  27  *   jmp.d32 \func
  28  *   ud1 %esp, %ecx
  29  *
  30  * That trailing #UD provides both a speculation stop and serves as a unique
  31  * 3 byte signature identifying static call trampolines. Also see tramp_ud[]
  32  * and __static_call_fixup().
  33  */
  34 #define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns)                    \
  35         asm(".pushsection .static_call.text, \"ax\"             \n"     \
  36             ".align 4                                           \n"     \
  37             ".globl " STATIC_CALL_TRAMP_STR(name) "             \n"     \
  38             STATIC_CALL_TRAMP_STR(name) ":                      \n"     \
  39             ANNOTATE_NOENDBR                                            \
  40             insns "                                             \n"     \
  41             ".byte 0x0f, 0xb9, 0xcc                             \n"     \
  42             ".type " STATIC_CALL_TRAMP_STR(name) ", @function   \n"     \
  43             ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
  44             ".popsection                                        \n")
  45
  46 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)                       \
  47         __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
  48
  49 #ifdef CONFIG_MITIGATION_RETHUNK
  50 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)                        \
  51         __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk")
  52 #else
  53 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)                        \
  54         __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
  55 #endif
  56
  57 #define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)                        \
  58         ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)
  59
  60 #define ARCH_ADD_TRAMP_KEY(name)                                        \
  61         asm(".pushsection .static_call_tramp_key, \"a\"         \n"     \
  62             ".long " STATIC_CALL_TRAMP_STR(name) " - .          \n"     \
  63             ".long " STATIC_CALL_KEY_STR(name) " - .            \n"     \
  64             ".popsection                                        \n")
  65
  66 extern bool __static_call_fixup(void *tramp, u8 op, void *dest);
  67
  68 #endif /* _ASM_STATIC_CALL_H */