ipipe: Introduce and use ipipe_root_nr_syscalls

At least one arch, infamous x86, has a difference of NR_syscalls
depending on compat vs. native ABI. Account for that by introducing a
function that can deliver the currently valid syscall number if an arch
implements such a service. In all other cases, this change is
functionally no difference.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

include/linux/ipipe_base.h

@@ -194,6 +194,10 @@ int __ipipe_notify_user_intreturn(void);
 
 #define __ipipe_serial_debug(__fmt, __args...)	raw_printk(__fmt, ##__args)
 
+#ifndef ipipe_root_nr_syscalls
+#define ipipe_root_nr_syscalls(ti)	NR_syscalls
+#endif
+
 #else /* !CONFIG_IPIPE */
 
 struct task_struct;

kernel/ipipe/core.c

@@ -1018,6 +1018,7 @@ int ipipe_handle_syscall(struct thread_info *ti,
 			 unsigned long nr, struct pt_regs *regs)
 {
 	unsigned long local_flags = READ_ONCE(ti->ipipe_flags);
+	unsigned int nr_syscalls = ipipe_root_nr_syscalls(ti);
 	int ret;
 
 	/*
@@ -1051,7 +1052,7 @@ int ipipe_handle_syscall(struct thread_info *ti,
 	 * system call handler.
 	 */
 
-	if (nr >= NR_syscalls && (local_flags & _TIP_HEAD)) {
+	if (nr >= nr_syscalls && (local_flags & _TIP_HEAD)) {
 		ipipe_fastcall_hook(regs);
 		local_flags = READ_ONCE(ti->ipipe_flags);
 		if (local_flags & _TIP_HEAD) {
@@ -1064,7 +1065,7 @@ int ipipe_handle_syscall(struct thread_info *ti,
 		}
 	}
 
-	if ((local_flags & _TIP_NOTIFY) || nr >= NR_syscalls) {
+	if ((local_flags & _TIP_NOTIFY) || nr >= nr_syscalls) {
 		ret =__ipipe_notify_syscall(regs);
 		local_flags = READ_ONCE(ti->ipipe_flags);
 		if (local_flags & _TIP_HEAD)