On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu [off-list ref] wrote:

+#define get_user(x,p)                                                  \
+       ({                                                              \
+               const register typeof(*(p)) __user *__p asm("$r0") = (p);\
+               register unsigned long __r2 asm("$r2");                 \
+               register int __e asm("$r0");                            \
+               switch (sizeof(*(__p))) {                               \
+               case 1:                                                 \
+                       __get_user_x(__r2, __p, __e, 1, "$lp");         \
+                       break;                                          \
+               case 2:                                                 \
+                       __get_user_x(__r2, __p, __e, 2, "$lp");         \
+                       break;                                          \
+               case 4:                                                 \
+                       __get_user_x(__r2, __p, __e, 4, "$lp");         \
+                       break;                                          \
+               case 8:                                                 \
+                       __get_user_x(__r2, __p, __e, 8, "$r3", "$lp");  \
+                       break;                                          \
+               default: __e = __get_user_bad(); break;                 \
+               }                                                       \
+               x = (typeof(*(p))) __r2;        \
+               __e;                                                    \
+       })

Something looks odd here: __get_user_bad above looks like it is meant
to provide a link-time error

+__get_user_bad_8:
+       move    $r3, #0
+__get_user_bad:
+       move    $r2, #0
+       move    $r0, #-EFAULT
+       ret
+

but here you actually have a symbol with that name, it gets turned
into a runtime error. I think the first one needs to get renamed to
actually work as expected and force the link error in built-in code
(it works in modules ins __get_user_bad is not exported).

+
+__put_user_bad:
+       move    $r0, #-EFAULT
+       ret
+

same here.

      Arnd