/* 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 "                                  \n"     \
            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 */