On 2017/6/29 14:33, Thomas Gleixner wrote: > On Thu, 29 Jun 2017, zhong jiang wrote: >> On 2017/6/29 6:13, Thomas Gleixner wrote: >>> That's simply wrong. If oparg is negative and the SHIFT bit is set then the >>> result is undefined today and there is no way that this can be used at >>> all. >>> >>> On x86: >>> >>> 1 << -1 = 0x80000000 >>> 1 << -2048 = 0x00000001 >>> 1 << -2047 = 0x00000002 >> but I test the cases in x86_64 all is zero. I wonder whether it is related to gcc or not >> >> zj.c:15:8: warning: left shift count is negative [-Wshift-count-negative] >> j = 1 << -2048; >> ^ >> [root@localhost zhongjiang]# ./zj >> j = 0 > Which is not a surprise because the compiler can detect it as the shift is > a constant. oparg is not so constant ... I get it. Thanks Thanks zhongjiang > Thanks, > > tglx > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
