Fix undefined behavior in OFFSET().

Accessing members of a null pointer is undefined behavior, even when only used to obtain the address again. So use a non-zero value as the base pointer address instead. 32 was chosen to provide sufficient alignment guarantees. Bug b/119823623 Change-Id: Ia6d24dd6c2740261948860c45eb35cc489a3a827 Reviewed-on: https://swiftshader-review.googlesource.com/c/22788Tested-by: Nicolas Capens <nicolascapens@google.com> Reviewed-by: Alexis Hétu <sugoi@google.com>

Fix undefined behavior in OFFSET().
0e6a044d · Nicolas Capens · Nicolas Capens · 46988abe · 0e6a044d
Commit 0e6a044d authored Nov 22, 2018 by Nicolas Capens Committed by Nicolas Capens Nov 23, 2018
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Types.hpp src/Common/Types.hpp +4 -1

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--- a/src/Common/Types.hpp
+++ b/src/Common/Types.hpp
@@ -151,7 +151,10 @@ namespace sw
 		return v;
 	}
-	#define OFFSET(s,m) (int)(size_t)&reinterpret_cast<const volatile char&>((((s*)0)->m))
+	// The OFFSET macro is a generalization of the offsetof() macro defined in <cstddef>.
+	// It allows e.g. getting the offset of array elements, even when indexed dynamically.
+	// We cast the address '32' and subtract it again, because null-dereference is undefined behavior.
+	#define OFFSET(s,m) ((int)(size_t)&reinterpret_cast<const volatile char&>((((s*)32)->m)) - 32)
 }
 #endif   // sw_Types_hpp