[PATCH v14 NEW ALT 1/3] safemath: Add ALIGN_UP_OVF() that checks for {over, under}flow

[Gao Xiang]

The following EROFS patch will use this helper to handle overflow
ALIGN_UP() cases.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
Hi Daniel,

I've also made another patch to conform Vladimir's and
Boyang's comments as much as I can.

Thanks,
Gao Xiang

 include/grub/safemath.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/grub/safemath.h b/include/grub/safemath.h
index fbd9b5925..bb8a5b39c 100644
--- a/include/grub/safemath.h
+++ b/include/grub/safemath.h
@@ -32,6 +32,22 @@
 
 #define grub_cast(a, res)      grub_add ((a), 0, (res))
 
+/*
+ * It's caller's responsibility that `align` should not equal to 0 and
+ * it must be a power of 2.
+ */
+#define ALIGN_UP_OVF(v, align, res)                    \
+({                                                     \
+  bool __failed;                                       \
+  typeof(v) __a = ((typeof(v))(align) - 1);            \
+                                                       \
+  __failed = grub_add (v, __a, res);                   \
+  if (__failed == false)                               \
+    {                                                  \
+      *(res) &= ~__a;                                  \
+    }                                                  \
+__failed;})
+
 #else
 #error gcc 5.1 or newer or clang 8.0 or newer is required
 #endif
-- 
2.39.3