On Tue, Mar 10, 2020 at 12:42:26PM +0000, Mark Brown wrote: > On Mon, Mar 09, 2020 at 09:05:05PM +0000, Mark Brown wrote: > > On Fri, Mar 06, 2020 at 10:27:29AM +0000, Catalin Marinas wrote: > > > > Does this series affect uprobes in any way? I.e. can you probe a landing > > > pad? > > > You can't probe a landing pad, uprobes on landing pads will be silently > > ignored so the program isn't disrupted, you just don't get the expected > > trace from those uprobes. This isn't new with the BTI support since > > the landing pads are generally pointer auth instructions, these already > > can't be probed regardless of what's going on with this series. It's > > already on the list to get sorted. > > Sorry, I realized thanks to Amit's off-list prompting that I was testing > that I was verifying with the wrong kernel binary here (user error since > it took me a while to sort out uprobes) so this isn't quite right - you > can probe the landing pads with or without this series. Can we not change aarch64_insn_is_nop() to actually return true only for NOP and ignore everything else in the hint space? We tend to re-use the hint instructions for new things in the architecture, so I'd rather white-list what we know we can safely probe than black-listing only some of the hint instructions. I haven't assessed the effort of doing the above (probably not a lot) but as a short-term workaround we could add the BTI and PAC hint instructions to the aarch64_insn_is_nop() (though my preferred option is the white-list one). -- Catalin
