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 insns " \n" \ 40 ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \ 41 ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \ 42 ".popsection \n") 43 44 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \ 45 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)") 46 47 #ifdef CONFIG_RETHUNK 48 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \ 49 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk") 50 #else 51 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \ 52 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop") 53 #endif 54 55 56 #define ARCH_ADD_TRAMP_KEY(name) \ 57 asm(".pushsection .static_call_tramp_key, \"a\" \n" \ 58 ".long " STATIC_CALL_TRAMP_STR(name) " - . \n" \ 59 ".long " STATIC_CALL_KEY_STR(name) " - . \n" \ 60 ".popsection \n") 61 62 extern bool __static_call_fixup(void *tramp, u8 op, void *dest); 63 64 #endif /* _ASM_STATIC_CALL_H */ 65