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Diffstat (limited to 'arch/x86/include/asm/static_call.h')
| -rw-r--r-- | arch/x86/include/asm/static_call.h | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/arch/x86/include/asm/static_call.h b/arch/x86/include/asm/static_call.h new file mode 100644 index 000000000000..c37f11999d0c --- /dev/null +++ b/arch/x86/include/asm/static_call.h @@ -0,0 +1,40 @@ +/* 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. + */ + +#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" \ + insns " \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)") + +#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \ + __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop") + +#endif /* _ASM_STATIC_CALL_H */ |