Quelle  static_call.h   Sprache: C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_STATIC_CALL_H
#define _ASM_STATIC_CALL_H

#include <asm/text-patching.h>

/*
 * For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
 * uses the current value of the key->func pointer to do an indirect jump to
 * the function.  This trampoline is only used during boot, before the call
 * sites get patched by static_call_update().  The name of this trampoline has
 * a magical aspect: objtool uses it to find static call sites so it can create
 * the .static_call_sites section.
 *
 * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
 * does a direct jump to the function.  The direct jump gets patched by
 * static_call_update().
 *
 * Having the trampoline in a special section forces GCC to emit a JMP.d32 when
 * it does tail-call optimization on the call; since you cannot compute the
 * relative displacement across sections.
 */

/*
 * The trampoline is 8 bytes and of the general form:
 *
 *   jmp.d32 \func
 *   ud1 %esp, %ecx
 *
 * That trailing #UD provides both a speculation stop and serves as a unique
 * 3 byte signature identifying static call trampolines. Also see tramp_ud[]
 * and __static_call_fixup().
 */
#define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns)   \
 asm(".pushsection .static_call.text, \"ax\" \n" \
     ".align 4 \n" \
     ".globl " STATIC_CALL_TRAMP_STR(name) " \n" \
     STATIC_CALL_TRAMP_STR(name) ": \n" \
     ANNOTATE_NOENDBR      \
     insns " \n" \
     ".byte 0x0f, 0xb9, 0xcc \n" \
     ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \
     ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
     ".popsection \n")

#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)   \
 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")

#ifdef CONFIG_MITIGATION_RETHUNK
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)   \
 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk")
#else
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)   \
 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
#endif

#define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)   \
 ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)

#define ARCH_ADD_TRAMP_KEY(name)     \
 asm(".pushsection .static_call_tramp_key, \"a\" \n" \
     ".long " STATIC_CALL_TRAMP_STR(name) " - . \n" \
     ".long " STATIC_CALL_KEY_STR(name) " - . \n" \
     ".popsection \n")

extern bool __static_call_fixup(void *tramp, u8 op, void *dest);

extern void __static_call_update_early(void *tramp, void *func);

#define static_call_update_early(name, _func)    \
({         \
 typeof(&STATIC_CALL_TRAMP(name)) __F = (_func);   \
 if (static_call_initialized) {     \
  __static_call_update(&STATIC_CALL_KEY(name),  \
         STATIC_CALL_TRAMP_ADDR(name), __F);\
 } else {       \
  WRITE_ONCE(STATIC_CALL_KEY(name).func, _func);  \
  __static_call_update_early(STATIC_CALL_TRAMP_ADDR(name),\
        __F);   \
 }        \
})

#endif /* _ASM_STATIC_CALL_H */