x86/extable: Annotate ex_handler_msr_mce() as a dead end

Fix

vmlinux.o: warning: objtool: fixup_exception+0x2d6: unreachable instruction

Signed-off-by: Borislav Petkov <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/include/asm/extable.h

···
 extern void early_fixup_exception(struct pt_regs *regs, int trapnr);
 
 #ifdef CONFIG_X86_MCE
-extern void ex_handler_msr_mce(struct pt_regs *regs, bool wrmsr);
+extern void __noreturn ex_handler_msr_mce(struct pt_regs *regs, bool wrmsr);
 #else
-static inline void ex_handler_msr_mce(struct pt_regs *regs, bool wrmsr) { }
+static inline void __noreturn ex_handler_msr_mce(struct pt_regs *regs, bool wrmsr)
+{
+	for (;;)
+		cpu_relax();
+}
 #endif
 
 #if defined(CONFIG_BPF_JIT) && defined(CONFIG_X86_64)

tools/objtool/check.c

···
 		"__invalid_creds",
 		"cpu_startup_entry",
 		"__ubsan_handle_builtin_unreachable",
+		"ex_handler_msr_mce",
 	};
 
 	if (!func)