Messages in this thread | | | Date | Tue, 6 Sep 2022 10:44:08 +0200 | From | Peter Zijlstra <> | Subject | Re: CONFIG_RETHUNK int3 filling prevents kprobes in function body |
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On Tue, Sep 06, 2022 at 10:33:29AM +0900, Masami Hiramatsu wrote: > On Mon, 5 Sep 2022 17:52:29 +0200 > Peter Zijlstra <peterz@infradead.org> wrote: > > > On Mon, Sep 05, 2022 at 05:09:16PM +0200, Peter Zijlstra wrote: > > > > > > This is because kprobes decodes function body to ensure the probed address > > > > is an instruction boundary, and if it finds the 0xcc (int3), it stops > > > > decoding and reject probing because the int3 is usually used for a > > > > software breakpoint and is replacing some other instruction. Without > > > > recovering the instruction, it can not continue decoding safely. > > > > > > I can't follow this logic. Decoding the single byte int3 instruction is > > > trivial. If you want a sanity check, follow the branches you found while > > > decoding the instruction starting at +0. > > > > Specifically, kprobe is the only one scribbling random [*] instructions > > with int3 in kernel text, so if kprobes doesn't know about the int3, it > > must be padding. > > No, kgdb is also handles int3 for its breakpoint. Of course we can > ignore it or ask kgdb to expose the API to decode it.
I'm thinking kgdb has worse issues anyway. Much of it seems to be wishful thinking.
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