Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 15 Feb 2023 11:25:54 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] x86/entry: Fix unwinding from kprobe on PUSH/POP instruction |
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On Tue, Feb 14, 2023 at 09:05:52AM -0800, Josh Poimboeuf wrote: > On Tue, Feb 14, 2023 at 12:35:04PM +0100, Peter Zijlstra wrote: > > On Mon, Feb 13, 2023 at 11:43:57PM +0900, Masami Hiramatsu wrote: > > > > > > Fix it by annotating the #BP exception as a non-signal stack frame, > > > > which tells the ORC unwinder to decrement the instruction pointer before > > > > looking up the corresponding ORC entry. > > > > > > Just to make it clear, this sounds like a 'hack' use of non-signal stack > > > frame. If so, can we change the flag name as 'literal' or 'non-literal' etc? > > > I concern that the 'signal' flag is used differently in the future. > > Agreed, though I'm having trouble coming up with a succinct yet > scrutable name. If length wasn't an issue it would be something like > > "decrement_return_address_when_looking_up_the_next_orc_entry" > > > Oooh, bike-shed :-) Let me suggest trap=1, where a trap is a fault with > > a different return address, specifically the instruction after the > > faulting instruction. > > I think "trap" doesn't work because > > 1) It's more than just traps, it's also function calls. We have > traps/calls in one bucket (decrement IP); and everything else > (faults, aborts, irqs) in the other (don't decrement IP). > > 2) It's not necessarily all traps which need the flag, just those that > affect a previously-but-now-overwritten stack-modifying instruction. > So #OF (which we don't use?) and trap-class #DB don't seem to be > affected. In practice maybe this distinction doesn't matter, but > for example there's no reason for ORC try to distinguish trap #DB > from non-trap #DB at runtime.
Well, I was specifically thinking about #DB, why don't we need to decrement when we put a hardware breakpoint on a stack modifying op?
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