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 */
69
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