libspl sys/sysmacros.h: Fix P2ROUNDUP_TYPED to not trigger integer ov…

…erflow The original P2ROUNDUP_TYPED macro contains a -x which triggers PaX's integer overflow detection for unsigned integers. Replace the macro with an equivalent version that does not trigger the overflow. Axioms: A. (-(x)) === (~((x) - 1)) === (~(x) + 1) under two's complement B. ~(x & y) === ((~(x)) | (~(y))) under De Morgan's law C. ~(~x) = x under the law of the excluded middle Proof: 0. (-(-(x) & -(align))) original 1. (~(-(x) & -(align)) + 1) by A 2. (((~(-(x))) | (~(-(align)))) + 1) by B 3. (((~(~((x) - 1))) | (~(~((align) - 1)))) + 1) by A 4. (((((x) - 1)) | (((align) - 1))) + 1) by C Signed-off-by: Jason Zaman <[email protected]> Reviewed-by: Chris Dunlop <[email protected]> Reviewed-by: Richard Yao <[email protected]>
openzfs · Oct 26, 2015 · 28a6a86 · 28a6a86
1 parent b23d543
commit 28a6a86
Showing 1 changed file with 2 additions and 4 deletions.
diff --git a/lib/libspl/include/sys/sysmacros.h b/lib/libspl/include/sys/sysmacros.h
@@ -49,9 +49,7 @@
  */
 #define	P2ALIGN(x, align)	((x) & -(align))
 #define	P2CROSS(x, y, align)	(((x) ^ (y)) > (align) - 1)
-#define	P2ROUNDUP(x, align)	(-(-(x) & -(align)))
-#define	P2ROUNDUP_TYPED(x, align, type) \
-				(-(-(type)(x) & -(type)(align)))
+#define	P2ROUNDUP(x, align)	((((x) - 1) | ((align) - 1)) + 1)
 #define	P2BOUNDARY(off, len, align) \
 				(((off) ^ ((off) + (len) - 1)) > (align) - 1)
 #define	P2PHASE(x, align)	((x) & ((align) - 1))
@@ -79,7 +77,7 @@
 #define	P2NPHASE_TYPED(x, align, type)		\
 	(-(type)(x) & ((type)(align) - 1))
 #define	P2ROUNDUP_TYPED(x, align, type)		\
-	(-(-(type)(x) & -(type)(align)))
+	((((type)(x) - 1) | ((type)(align) - 1)) + 1)
 #define	P2END_TYPED(x, align, type)		\
 	(-(~(type)(x) & -(type)(align)))
 #define	P2PHASEUP_TYPED(x, align, phase, type)	\