x86/runtime-const: Add the RUNTIME_CONST_PTR assembly macro

Add an assembly macro to refer runtime cost. It hides linker magic and
makes assembly more readable.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/include/asm/runtime-const.h

···
 #ifndef _ASM_RUNTIME_CONST_H
 #define _ASM_RUNTIME_CONST_H
 
+#ifdef __ASSEMBLY__
+
+.macro RUNTIME_CONST_PTR sym reg
+	movq	$0x0123456789abcdef, %\reg
+	1:
+	.pushsection runtime_ptr_\sym, "a"
+	.long	1b - 8 - .
+	.popsection
+.endm
+
+#else /* __ASSEMBLY__ */
+
 #define runtime_const_ptr(sym) ({				\
 	typeof(sym) __ret;					\
 	asm_inline("mov %1,%0\n1:\n"				\
···
 	}
 }
 
+#endif /* __ASSEMBLY__ */
 #endif

arch/x86/lib/getuser.S

···
 #include <asm/thread_info.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/runtime-const.h>
 
 #define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
 
 .macro check_range size:req
 .if IS_ENABLED(CONFIG_X86_64)
-	movq $0x0123456789abcdef,%rdx
-  1:
-  .pushsection runtime_ptr_USER_PTR_MAX,"a"
-	.long 1b - 8 - .
-  .popsection
+	RUNTIME_CONST_PTR USER_PTR_MAX, rdx
 	cmp %rdx, %rax
 	cmova %rdx, %rax
 .else