On Fri, Apr 29, 2016 at 03:36:12PM -0700, Dave Hansen wrote: > On 04/29/2016 03:30 PM, Yu-cheng Yu wrote: > > On Fri, Apr 29, 2016 at 01:25:34PM -0700, Dave Hansen wrote: > >> On 03/04/2016 10:12 AM, Yu-cheng Yu wrote: > >>> + for (i = 0; i < XFEATURE_MAX; i++) { > >>> + /* > >>> + * Copy only in-use xstates. > >>> + */ > >>> + if (((header.xfeatures >> i) & 1) && xfeature_enabled(i)) { > >>> + void *src = get_xsave_addr_no_check(xsave, i); > >> > >> How could a bit in header.xfeatures get set if it is not set in > >> xfeature_enabled() aka xfeatures_mask aka XCR0? > > > > Do you mean, we should test xfeature_enabled(i) first, like, > > > > if (xfeature_enabled(i) && ((header.xfeatures >> i) & 1)) ? > > > > The result will be the same, like you said, if XCR0[i] is not set, > > hader.xfeatures[i] cannot be set. But if XCR0[i] is set, > > header.xfeatures[i] can be cleared. > > I think the xfeature_enabled(i) is probably redundant. Does it serve > any actual purpose?
Got it.