On Tue, Apr 28, 2020 at 04:16:14PM +0200, Peter Zijlstra wrote: > On Tue, Apr 28, 2020 at 02:46:27PM +0200, Peter Zijlstra wrote: > > On Tue, Apr 28, 2020 at 02:04:50AM -0500, Josh Poimboeuf wrote: > > > > I'm thinking something like this should fix it. Peter, does this look > > > ok? > > > > Unfortunate. But also, I fear, insufficient. Specifically consider > > things like: > > > > ALTERNATIVE "jmp 1f", > > "alt... > > "..." > > "...insn", X86_FEAT_foo > > 1: > > > > This results in something like: > > > > > > .text .altinstr_replacement > > e8 xx ... > > 90 > > 90 > > ... > > 90 > > > > Where all our normal single byte nops (0x90) are unreachable with > > undefined CFI, but the alternative might have CFI, which is never > > propagated. > > > > We ran into this with the validate_alternative stuff from Alexandre. > > > So rather than hacking around this issue, should we not make > > create_orc() smarter? > > > > I'm trying to come up with something, but so far I'm just making a mess. > > Like this, it's horrid, but it seems to work. > > What do you think of the approach? I'll work on cleaning it up if you > don't hate it too much ;-)
How'd you know I'd hate it ;-) That's quite the monstrosity, and I still don't see the point. I thought we decided to just disallow CFI changes in alternatives anyway? That can be done much simpler. -- Josh
