x86/entry: Refactor SYSCALL_DEFINE0 macros

Pull the common code out from the SYSCALL_DEFINE0 macros into a new
__SYS_STUB0 macro.  Also conditionalize the X64 version in preparation for
enabling syscall wrappers on 32-bit native kernels.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200313195144.164260-3-brgerst@gmail.com

arch/x86/include/asm/syscall_wrapper.h

@@ -21,6 +21,12 @@ struct pt_regs;
 	      ,,(unsigned int)regs->dx,,(unsigned int)regs->si		\
 	      ,,(unsigned int)regs->di,,(unsigned int)regs->bp)
 
+#define __SYS_STUB0(abi, name)						\
+	asmlinkage long __##abi##_##name(const struct pt_regs *regs);	\
+	ALLOW_ERROR_INJECTION(__##abi##_##name, ERRNO);			\
+	asmlinkage long __##abi##_##name(const struct pt_regs *regs)	\
+		__alias(__do_##name);
+
 #define __SYS_STUBx(abi, name, ...)					\
 	asmlinkage long __##abi##_##name(const struct pt_regs *regs);	\
 	ALLOW_ERROR_INJECTION(__##abi##_##name, ERRNO);			\
@@ -30,10 +36,14 @@ struct pt_regs;
 	}
 
 #ifdef CONFIG_X86_64
+#define __X64_SYS_STUB0(name)						\
+	__SYS_STUB0(x64, sys_##name)
+
 #define __X64_SYS_STUBx(x, name, ...)					\
 	__SYS_STUBx(x64, sys##name,					\
 		    SC_X86_64_REGS_TO_ARGS(x, __VA_ARGS__))
 #else /* CONFIG_X86_64 */
+#define __X64_SYS_STUB0(name)
 #define __X64_SYS_STUBx(x, name, ...)
 #endif /* CONFIG_X86_64 */
 
@@ -46,34 +56,20 @@ struct pt_regs;
  * kernel/sys_ni.c and SYS_NI in kernel/time/posix-stubs.c to cover this
  * case as well.
  */
-#define __IA32_COMPAT_SYS_STUB0(x, name)				\
-	asmlinkage long __ia32_compat_sys_##name(const struct pt_regs *regs);\
-	ALLOW_ERROR_INJECTION(__ia32_compat_sys_##name, ERRNO);		\
-	asmlinkage long __ia32_compat_sys_##name(const struct pt_regs *regs)\
-	{								\
-		return __se_compat_sys_##name();			\
-	}
+#define __IA32_COMPAT_SYS_STUB0(name)					\
+	__SYS_STUB0(ia32, compat_sys_##name)
 
 #define __IA32_COMPAT_SYS_STUBx(x, name, ...)				\
 	__SYS_STUBx(ia32, compat_sys##name,				\
 		    SC_IA32_REGS_TO_ARGS(x, __VA_ARGS__))
 
+#define __IA32_SYS_STUB0(name)						\
+	__SYS_STUB0(ia32, sys_##name)
+
 #define __IA32_SYS_STUBx(x, name, ...)					\
 	__SYS_STUBx(ia32, sys##name,					\
 		    SC_IA32_REGS_TO_ARGS(x, __VA_ARGS__))
 
-/*
- * To keep the naming coherent, re-define SYSCALL_DEFINE0 to create an alias
- * named __ia32_sys_*()
- */
-
-#define SYSCALL_DEFINE0(sname)						\
-	SYSCALL_METADATA(_##sname, 0);					\
-	asmlinkage long __x64_sys_##sname(const struct pt_regs *__unused);\
-	ALLOW_ERROR_INJECTION(__x64_sys_##sname, ERRNO);		\
-	SYSCALL_ALIAS(__ia32_sys_##sname, __x64_sys_##sname);		\
-	asmlinkage long __x64_sys_##sname(const struct pt_regs *__unused)
-
 #define COND_SYSCALL(name)							\
 	asmlinkage __weak long __x64_sys_##name(const struct pt_regs *__unused)	\
 	{									\
@@ -89,7 +85,9 @@ struct pt_regs;
 	SYSCALL_ALIAS(__ia32_sys_##name, sys_ni_posix_timers)
 
 #else /* CONFIG_IA32_EMULATION */
+#define __IA32_COMPAT_SYS_STUB0(name)
 #define __IA32_COMPAT_SYS_STUBx(x, name, ...)
+#define __IA32_SYS_STUB0(name)
 #define __IA32_SYS_STUBx(x, name, ...)
 #endif /* CONFIG_IA32_EMULATION */
 
@@ -100,20 +98,15 @@ struct pt_regs;
  * of the x86-64-style parameter ordering of x32 syscalls. The syscalls common
  * with x86_64 obviously do not need such care.
  */
-#define __X32_COMPAT_SYS_STUB0(x, name, ...)				\
-	asmlinkage long __x32_compat_sys_##name(const struct pt_regs *regs);\
-	ALLOW_ERROR_INJECTION(__x32_compat_sys_##name, ERRNO);		\
-	asmlinkage long __x32_compat_sys_##name(const struct pt_regs *regs)\
-	{								\
-		return __se_compat_sys_##name();\
-	}
+#define __X32_COMPAT_SYS_STUB0(name)					\
+	__SYS_STUB0(x32, compat_sys_##name)
 
 #define __X32_COMPAT_SYS_STUBx(x, name, ...)				\
 	__SYS_STUBx(x32, compat_sys##name,				\
 		    SC_X86_64_REGS_TO_ARGS(x, __VA_ARGS__))
 
 #else /* CONFIG_X86_X32 */
-#define __X32_COMPAT_SYS_STUB0(x, name)
+#define __X32_COMPAT_SYS_STUB0(name)
 #define __X32_COMPAT_SYS_STUBx(x, name, ...)
 #endif /* CONFIG_X86_X32 */
 
@@ -125,15 +118,12 @@ struct pt_regs;
  * of them.
  */
 #define COMPAT_SYSCALL_DEFINE0(name)					\
-	static long __se_compat_sys_##name(void);			\
-	static inline long __do_compat_sys_##name(void);		\
-	__IA32_COMPAT_SYS_STUB0(x, name)				\
-	__X32_COMPAT_SYS_STUB0(x, name)					\
-	static long __se_compat_sys_##name(void)			\
-	{								\
-		return __do_compat_sys_##name();			\
-	}								\
-	static inline long __do_compat_sys_##name(void)
+	static asmlinkage long						\
+	__do_compat_sys_##name(const struct pt_regs *__unused);		\
+	__IA32_COMPAT_SYS_STUB0(name)					\
+	__X32_COMPAT_SYS_STUB0(name)					\
+	static asmlinkage long						\
+	__do_compat_sys_##name(const struct pt_regs *__unused)
 
 #define COMPAT_SYSCALL_DEFINEx(x, name, ...)					\
 	static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
@@ -216,13 +206,14 @@ struct pt_regs;
  * SYSCALL_DEFINEx() -- which is essential for the COND_SYSCALL() and SYS_NI()
  * macros to work correctly.
  */
-#ifndef SYSCALL_DEFINE0
 #define SYSCALL_DEFINE0(sname)						\
 	SYSCALL_METADATA(_##sname, 0);					\
-	asmlinkage long __x64_sys_##sname(const struct pt_regs *__unused);\
-	ALLOW_ERROR_INJECTION(__x64_sys_##sname, ERRNO);		\
-	asmlinkage long __x64_sys_##sname(const struct pt_regs *__unused)
-#endif
+	static asmlinkage long						\
+	__do_sys_##sname(const struct pt_regs *__unused);		\
+	__X64_SYS_STUB0(sname)						\
+	__IA32_SYS_STUB0(sname)						\
+	static asmlinkage long						\
+	__do_sys_##sname(const struct pt_regs *__unused)
 
 #ifndef COND_SYSCALL
 #define COND_SYSCALL(name) 							\