(2014/04/10 22:41), Denys Vlasenko wrote: > On 04/09/2014 05:43 PM, Oleg Nesterov wrote: >> On 04/08, Jim Keniston wrote: >>> >>> On Sun, 2014-04-06 at 22:16 +0200, Oleg Nesterov wrote: >>>> 0xe8. Anything else? >>> >>> No, I think e8 is the only call instruction uprobes will see. >> >> Good. > > There is this monstrosity, "16-bit override for branches" in 64-mode: > > 66 e8 nn nn callw <offset16> > > Nobody sane uses it because it truncates instruction pointer.
No problem, insn.c can handle that too. :) Thank you, > > Or rather, *I think* it should truncate it (i.e. zero-extend to full width), > but conceivably some CPUs can be buggy wrt that: > they can decide to modify only lower 16 bits of IP, > or even they can decided to use signed <offset16> but apply it > to full-width RIP. > > AMD manuals are not clear on what exactly should happen. > > I am sure no one sane uses this form of branch instructions > in 32-bit and 64-bit code. > > I don't think we should be trying to support it "correctly" > (we can just let program crash with SIGILL or something), > we only need to make sure we don't overlook its existence > and thus are not tricked into touching or modifying unrelated data. > > > Imagine that 66 e8 nn nn bytes are exactly at the end of > a page, and we wrongly assume that offset is 32-bit, not 16-bit. > > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
