Add comment about usage on EFI_SIZE_TO_PAGES() and EFI_PAGES_TO_SIZE macros.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11004 6f19259b-4bc3-4df7-8a09-765794883524

diff --git a/MdePkg/Include/Uefi/UefiBaseType.h b/MdePkg/Include/Uefi/UefiBaseType.h
index 6e522807daf6fc49e013d8f4c7a000e0a8c453ea..5b8a7620728f6e899cd512864a0017d239a0b86c 100644 (file)
--- a/MdePkg/Include/Uefi/UefiBaseType.h
+++ b/MdePkg/Include/Uefi/UefiBaseType.h
@@ -188,8 +188,12 @@ typedef union {
 #define EFI_PAGE_MASK             0xFFF\r
 #define EFI_PAGE_SHIFT            12\r
 \r
+//\r
+// It is expected that a parameter for the following two macros is of type UINTN.\r
+// Be careful to pass a UINT64 parameter because 32-bit build break may happen\r
+// if << or >> shift operations are performed on a 64-bit integer with 32-bit C compiler.\r
+//\r
 #define EFI_SIZE_TO_PAGES(a)  (((a) >> EFI_PAGE_SHIFT) + (((a) & EFI_PAGE_MASK) ? 1 : 0))\r
-\r
 #define EFI_PAGES_TO_SIZE(a)   ( (a) << EFI_PAGE_SHIFT)\r
 \r
 ///\r