[PATCH] arm: OABI compat: fix build when EPOLL is not enabled

[Randy Dunlap]

When CONFIG_EPOLL is not set/enabled, sys_oabi-compat.c has build
errors. Fix these by surrounding them with ifdef CONFIG_EPOLL/endif
and providing stubs for the "EPOLL is not set" case.

../arch/arm/kernel/sys_oabi-compat.c: In function 'sys_oabi_epoll_ctl':
../arch/arm/kernel/sys_oabi-compat.c:257:6: error: implicit declaration of function 'ep_op_has_event' [-Werror=implicit-function-declaration]
  257 |  if (ep_op_has_event(op) &&
      |      ^~~~~~~~~~~~~~~
../arch/arm/kernel/sys_oabi-compat.c:264:9: error: implicit declaration of function 'do_epoll_ctl'; did you mean 'sys_epoll_ctl'? [-Werror=implicit-function-declaration]
  264 |  return do_epoll_ctl(epfd, op, fd, &kernel, false);
      |         ^~~~~~~~~~~~

Fixes: 687ad0191488 ("[ARM] 3109/1: old ABI compat: syscall wrappers for ABI impedance matching")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx> # from an lkp .config file
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: Nicolas Pitre <nico@xxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
---
or does OABI require epoll? how is that enforced?

 arch/arm/kernel/sys_oabi-compat.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- linux-next-20201214.orig/arch/arm/kernel/sys_oabi-compat.c
+++ linux-next-20201214/arch/arm/kernel/sys_oabi-compat.c
@@ -248,6 +248,7 @@ struct oabi_epoll_event {
 	__u64 data;
 } __attribute__ ((packed,aligned(4)));
 
+#ifdef CONFIG_EPOLL
 asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
 				   struct oabi_epoll_event __user *event)
 {
@@ -298,6 +299,20 @@ asmlinkage long sys_oabi_epoll_wait(int
 	kfree(kbuf);
 	return err ? -EFAULT : ret;
 }
+#else
+asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
+				   struct oabi_epoll_event __user *event)
+{
+	return -EINVAL;
+}
+
+asmlinkage long sys_oabi_epoll_wait(int epfd,
+				    struct oabi_epoll_event __user *events,
+				    int maxevents, int timeout)
+{
+	return -EINVAL;
+}
+#endif
 
 struct oabi_sembuf {
 	unsigned short	sem_num;