arm64: introduce syscall_fn_t

In preparation for invoking arbitrary syscalls from C code, let's define
a type for an arbitrary syscall, matching the parameter passing rules of
the AAPCS.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/syscall.h

@@ -20,7 +20,11 @@
 #include <linux/compat.h>
 #include <linux/err.h>
 
-extern const void *sys_call_table[];
+typedef long (*syscall_fn_t)(unsigned long, unsigned long,
+			     unsigned long, unsigned long,
+			     unsigned long, unsigned long);
+
+extern const syscall_fn_t sys_call_table[];
 
 static inline int syscall_get_nr(struct task_struct *task,
 				 struct pt_regs *regs)

arch/arm64/kernel/sys.c

@@ -25,7 +25,9 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/syscalls.h>
+
 #include <asm/cpufeature.h>
+#include <asm/syscall.h>
 
 asmlinkage long sys_mmap(unsigned long addr, unsigned long len,
 			 unsigned long prot, unsigned long flags,
@@ -52,13 +54,13 @@ asmlinkage long sys_rt_sigreturn(void);
 #define sys_personality		sys_arm64_personality
 
 #undef __SYSCALL
-#define __SYSCALL(nr, sym)	[nr] = sym,
+#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)sym,
 
 /*
  * The sys_call_table array must be 4K aligned to be accessible from
  * kernel/entry.S.
  */
-void * const sys_call_table[__NR_syscalls] __aligned(4096) = {
-	[0 ... __NR_syscalls - 1] = sys_ni_syscall,
+const syscall_fn_t sys_call_table[__NR_syscalls] __aligned(4096) = {
+	[0 ... __NR_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
 #include <asm/unistd.h>
 };

arch/arm64/kernel/sys32.c

@@ -25,6 +25,8 @@
 #include <linux/compiler.h>
 #include <linux/syscalls.h>
 
+#include <asm/syscall.h>
+
 asmlinkage long compat_sys_sigreturn(void);
 asmlinkage long compat_sys_rt_sigreturn(void);
 asmlinkage long compat_sys_statfs64_wrapper(void);
@@ -40,13 +42,13 @@ asmlinkage long compat_sys_fallocate_wrapper(void);
 asmlinkage long compat_sys_mmap2_wrapper(void);
 
 #undef __SYSCALL
-#define __SYSCALL(nr, sym)	[nr] = sym,
+#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)sym,
 
 /*
  * The sys_call_table array must be 4K aligned to be accessible from
  * kernel/entry.S.
  */
-void * const compat_sys_call_table[__NR_compat_syscalls] __aligned(4096) = {
-	[0 ... __NR_compat_syscalls - 1] = sys_ni_syscall,
+const syscall_fn_t compat_sys_call_table[__NR_compat_syscalls] __aligned(4096) = {
+	[0 ... __NR_compat_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
 #include <asm/unistd32.h>
 };