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 #define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns) \ 25 asm(".pushsection .static_call.text, \"ax\" \n" \ 26 ".align 4 \n" \ 27 ".globl " STATIC_CALL_TRAMP_STR(name) " \n" \ 28 STATIC_CALL_TRAMP_STR(name) ": \n" \ 29 insns " \n" \ 30 ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \ 31 ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \ 32 ".popsection \n") 33 34 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \ 35 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)") 36 37 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \ 38 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop") 39 40 #endif /* _ASM_STATIC_CALL_H */ 41