From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: Re: [PATCH v10 1/5] add infrastructure for tagging functions as error injectable Date: Wed, 20 Dec 2017 16:13:42 +0900 Message-ID: <20171220161342.44443047f186b7a62efdfe1a@kernel.org> References: <1513365176-6744-1-git-send-email-josef@toxicpanda.com> <1513365176-6744-2-git-send-email-josef@toxicpanda.com> <20171219152925.5789309c6c4d27807d42f11c@kernel.org> <7b73cbfa-959f-2efe-8a7c-f9d0b0c2ccaa@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Josef Bacik , , , , , , , , , , , Josef Bacik To: Alexei Starovoitov Return-path: Received: from mail.kernel.org ([198.145.29.99]:47632 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304AbdLTHNr (ORCPT ); Wed, 20 Dec 2017 02:13:47 -0500 In-Reply-To: <7b73cbfa-959f-2efe-8a7c-f9d0b0c2ccaa@fb.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 19 Dec 2017 18:14:17 -0800 Alexei Starovoitov wrote: > On 12/18/17 10:29 PM, Masami Hiramatsu wrote: > >> > >> +#if defined(__KERNEL__) && !defined(__ASSEMBLY__) > >> +#ifdef CONFIG_BPF_KPROBE_OVERRIDE > > > > BTW, CONFIG_BPF_KPROBE_OVERRIDE is also confusable name. > > Since this feature override a function to just return with > > some return value (as far as I understand, or would you > > also plan to modify execution path inside a function?), > > I think it should be better CONFIG_BPF_FUNCTION_OVERRIDE or > > CONFIG_BPF_EXECUTION_OVERRIDE. > > I don't think such renaming makes sense. > The feature is overriding kprobe by changing how kprobe returns. > It doesn't override BPF_FUNCTION or BPF_EXECUTION. No, I meant this is BPF's feature which override FUNCTION, so BPF is a kind of namespace. (Is that only for a function entry because it can not tweak stackframe at this morment?) > The kernel enters and exists bpf program as normal. Yeah, but that bpf program modifies instruction pointer, am I correct? > > > Indeed, BPF is based on kprobes, but it seems you are limiting it > > with ftrace (function-call trace) (I'm not sure the reason why), > > so using "kprobes" for this feature seems strange for me. > > do you have an idea how kprobe override can happen when kprobe > placed in the middle of the function? For example, if you know a basic block in the function, maybe you can skip a block or something like that. But nowadays it is somewhat hard because optimizer mixed it up. > > Please make your suggestion as patches based on top of bpf-next. bpf-next seems already pick this series. Would you mean I revert it and write new patch? Thank you, > > Thanks > -- Masami Hiramatsu