1 files changed, 68 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 000000000..343b722cc
--- /dev/null
+++ b/arch/x86/include/asm/static_call.h
@@ -0,0 +1,68 @@
+/* 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.
+ */
+
+/*
+ * The trampoline is 8 bytes and of the general form:
+ *
+ *   jmp.d32 \func
+ *   ud1 %esp, %ecx
+ *
+ * That trailing #UD provides both a speculation stop and serves as a unique
+ * 3 byte signature identifying static call trampolines. Also see tramp_ud[]
+ * and __static_call_fixup().
+ */
+#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"	\
+	    ANNOTATE_NOENDBR						\
+	    insns "						\n"	\
+	    ".byte 0x0f, 0xb9, 0xcc				\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)")
+
+#ifdef CONFIG_RETHUNK
+#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\
+	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk")
+#else
+#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\
+	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
+#endif
+
+#define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)			\
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)
+
+#define ARCH_ADD_TRAMP_KEY(name)					\
+	asm(".pushsection .static_call_tramp_key, \"a\"		\n"	\
+	    ".long " STATIC_CALL_TRAMP_STR(name) " - .		\n"	\
+	    ".long " STATIC_CALL_KEY_STR(name) " - .		\n"	\
+	    ".popsection					\n")
+
+extern bool __static_call_fixup(void *tramp, u8 op, void *dest);
+
+#endif /* _ASM_STATIC_CALL_H */