diff options
| author | Jason Zaman <[email protected]> | 2015-10-24 14:01:08 +0800 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2015-11-16 16:10:07 -0800 |
| commit | 5c790678f1a5231b75be174eb8a02e15dfe9b4d5 (patch) | |
| tree | 8b24f0f99ddc34ac640b6aca8711cdeb496d0a7b /lib/libspl | |
| parent | 27a19a0d5a5297f399eaa6eca86dc4047e484078 (diff) | |
sysmacros: Make P2ROUNDUP not trigger int overflow
The original P2ROUNDUP and P2ROUNDUP_TYPED macros contain -x which
triggers PaX's integer overflow detection for unsigned integers.
Replace the macros 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 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
Q.E.D.
Signed-off-by: Jason Zaman <[email protected]>
Reviewed-by: Chris Dunlop <[email protected]>
Reviewed-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #3949
Diffstat (limited to 'lib/libspl')
| -rw-r--r-- | lib/libspl/include/sys/sysmacros.h | 6 |
1 files changed, 2 insertions, 4 deletions
diff --git a/lib/libspl/include/sys/sysmacros.h b/lib/libspl/include/sys/sysmacros.h index 698b0a7a3..5d10657be 100644 --- 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) \ |