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
66extern bool __static_call_fixup(void *tramp, u8 op, void *dest);
67
68#endif /* _ASM_STATIC_CALL_H */
69