On Wed, May 4, 2016 at 7:06 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote: >> On 05/04/2016 02:56 PM, H. Peter Anvin wrote: >> >> Beware that shifting by an amount >= the number of bits in the >> >> word remains Undefined Behavior. >> >> > This construct has been supported as a rotate since at least gcc2. >> >> How then should we understand the story told in commit d7e35dfa? >> Is the story wrong? > > I don't think Linux runs on a system where it would make a difference > (like a VAX), and also gcc always converts it before it could. > Even UBSan should not complain because it runs after the conversion > to ROTATE. > >From what I understand, its a limitation in the barrel shifter and the way the shift bits are handled. Linux runs on a great number of devices, so its conceivable (likely?) a low-cost board would have hardware limitations that not found in modern desktops and servers or VAX. Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
