Fix alignment on AIX (GH #745)

1 files changed, 14 insertions, 12 deletions

diff --git a/secblock.h b/secblock.h
index 4ad7c381..26ebd0ae 100644
--- a/secblock.h
+++ b/secblock.h
@@ -484,17 +484,15 @@ private:
 	// align the stack to 8-bytes or less by default, not 16-bytes as

 	// requested. Additionally, the AIX linker seems to use 4-bytes

 	// by default. However, all linkers tested appear to honor

-	// CRYPTOPP_ALIGN_DATA(8). Given we can achieve 8-byte array

-	// alignment, we needs to transform the address returned from

-	// GetAlignedArray() to a 16-byte alignment.

-	// Also see http://stackoverflow.com/a/1468656/608639.

+	// CRYPTOPP_ALIGN_DATA(8). Also see

+	// http://stackoverflow.com/a/1468656/608639.

 	//

 	// The 16-byte alignment is achieved by padding the requested

-	// size with extra elements so we have at least 8-bytes of slack

+	// size with extra elements so we have at least 16-bytes of slack

 	// to work with. Then the pointer is moved down to achieve a

 	// 16-byte alignment (stacks grow down).

 	//

-	// The additional 8-bytes introduces a small secondary issue.

+	// The additional 16-bytes introduces a small secondary issue.

 	// The secondary issue is, a large T results in 0 = 8/sizeof(T).

 	// The library is OK but users may hit it. So we need to guard

 	// for a large T, and that is what PAD achieves.

@@ -506,19 +504,23 @@ private:
 		CRYPTOPP_ASSERT(p_array+S <= m_array+(S+PAD));

 		return p_array;

 	}

+

+#   if defined(_AIX)

+	// PAD is elements, not bytes, and rounded up to ensure no overflow.

+	enum { Q = sizeof(T), PAD = (Q >= 16) ? 1 : (Q >= 8) ? 2 : (Q >= 4) ? 4 : (Q >= 2) ? 8 : 16 };

+	CRYPTOPP_ALIGN_DATA(8) T m_array[S+PAD];

+#   else

 	// PAD is elements, not bytes, and rounded up to ensure no overflow.

 	enum { Q = sizeof(T), PAD = (Q >= 8) ? 1 : (Q >= 4) ? 2 : (Q >= 2) ? 4 : 8 };

 	CRYPTOPP_ALIGN_DATA(8) T m_array[S+PAD];

+#   endif

 

 #else

 

-	// The 8-byte alignments follows convention of Linux and Windows.

-	// Linux and Windows receives most testing. Duplicate it here for

-	// other platforms like AIX and Solaris. AIX and Solaris often use

-	// alignments smaller than expected. In fact AIX caught us by

-	// surprise with word16 and word32.

+	// CRYPTOPP_BOOL_ALIGN16 is 0. Use natural alignment of T.

 	T* GetAlignedArray() {return m_array;}

-	CRYPTOPP_ALIGN_DATA(8) T m_array[S];

+	CRYPTOPP_ALIGN_DATA(4) T m_array[S];

+

 #endif

 

 	A m_fallbackAllocator;