On 10/20/2014 10:09 AM, Daniel Borkmann wrote: > On 10/20/2014 03:58 PM, Andrey Ryabinin wrote: >> On 10/20/2014 04:49 PM, Theodore Ts'o wrote: >>> On Mon, Oct 20, 2014 at 03:03:22PM +0400, Andrey Ryabinin wrote: >>>> Hi, Theodore. >>>> >>>> I've got this while booting kernel with ubsan: >>>> >>>> [ 0.000000] ================================================================================ >>>> [ 0.000000] UBSan: Undefined behaviour in ../include/linux/bitops.h:107:33 >>>> [ 0.000000] shift exponent 32 is to large for 32-bit type 'unsigned int' >>> ... >>>> [ 0.000000] _mix_pool_bytes (/home/andrew/linux/ubsan_x86//include/linux/bitopsh:107 /home/andrew/linux/ubsan_x86//drivers/char/randomc:509) >>> >>> So this doesn't make any sense to me. This is triggering here: >>> >>> w = rol32(*bytes++, input_rotate); >>> >>> .... but input_rotate should never be >= 32, since it is set this way: >>> >> >> It's triggering when input_rotate == 0, so UBSan complains about right shift in rol32() >> >> static inline __u32 rol32(__u32 word, unsigned int shift) >> { >> return (word << shift) | (word >> (32 - shift)); >> } > > So that would be the case when the entropy store's input_rotate calls > _mix_pool_bytes() for the very first time ... I don't think it's an > issue though. It's an issue because it's _undefined_. For all you know gcc could return whatever it wants as the result (42?) - no one promises you a "0" there. Thanks, Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html