[PATCH] cobalt: Improve cobalt_copy_from/to_user

[Jan Kiszka]

From: Jan Kiszka <jan.kiszka at siemens.com>

This aligns the definition of our user copy services with the kernel in
two aspects:
 - use unlikely to mark the fast path
 - memset the remaining bits of the target region if the copy fails;
   this avoids false-positive compiler warnings and reduces the risk to
   evaluate undefined data in case the return value is not checked

Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>
---
 kernel/cobalt/include/asm-generic/xenomai/syscall.h | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/cobalt/include/asm-generic/xenomai/syscall.h b/kernel/cobalt/include/asm-generic/xenomai/syscall.h
index 7909fc310a..e14a9d1e3b 100644
--- a/kernel/cobalt/include/asm-generic/xenomai/syscall.h
+++ b/kernel/cobalt/include/asm-generic/xenomai/syscall.h
@@ -46,15 +46,25 @@
 static inline int cobalt_copy_from_user(void *dst, const void __user *src,
 					size_t size)
 {
-	return (!access_rok(src, size) ||
-		__xn_copy_from_user(dst, src, size)) ? -EFAULT : 0;
+	size_t remaining = size;
+
+	if (likely(access_rok(src, size)))
+		remaining = __xn_copy_from_user(dst, src, size);
+
+	if (unlikely(remaining > 0)) {
+		memset(dst + (size - remaining), 0, remaining);
+		return -EFAULT;
+	}
+	return 0;
 }
 
 static inline int cobalt_copy_to_user(void __user *dst, const void *src,
 				      size_t size)
 {
-	return (!access_wok(dst, size) ||
-		__xn_copy_to_user(dst, src, size)) ? -EFAULT : 0;
+	if (unlikely(!access_wok(dst, size) ||
+	    __xn_copy_to_user(dst, src, size)))
+		return -EFAULT;
+	return 0;
 }
 
 static inline int cobalt_strncpy_from_user(char *dst, const char __user *src,
-- 
2.16.4