On Fri, Mar 26, 2010 at 11:03:09AM -0700, Linus Torvalds wrote: > On Fri, 26 Mar 2010, Ralf Baechle wrote: > > "The documentation on the 80386 and 80486 states that op1 is undefined if > > op2 is 0. In reality the 80386 will leave the value in op1 unchanged. > > The first versions of the 80486 will change op1 to an undefined value. > > Later version again will leave it unchanged." > > > > [1] Die Intel Familie in German language, by Robert Hummel, 1992 > > Ok, that explains my memory of us having tried this, at least. > > But I do wonder if any of the people working for Intel could ask the CPU > architects whether we could depend on the "don't write" for 64-bit mode. > If AMD already documents the don't-touch semantics, and if Intel were to > be ok with documenting it for their 64-bit capable CPU's, we wouldn't then > need to rely on undefined behavior. I don't know whether we can get it /documented/, but the architect I asked said "We'll never get away with reverting to the older behavior, so in essence the architecture is set to not overwrite." -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
