From: Jiri Olsa <olsajiri@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Olsa <olsajiri@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, Martin KaFai Lau <kafai@fb.com>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
"Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Subject: Re: [PATCHv2 bpf-next 2/6] ftrace: Keep the resolved addr in kallsyms_callback
Date: Tue, 16 Aug 2022 09:06:00 +0200 [thread overview]
Message-ID: <YvtB2OrqmzRGzyPr@krava> (raw)
In-Reply-To: <YvpAAitklP35uCZo@worktop.programming.kicks-ass.net>
On Mon, Aug 15, 2022 at 02:45:54PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 15, 2022 at 12:30:46PM +0200, Jiri Olsa wrote:
> > On Mon, Aug 15, 2022 at 12:13:39PM +0200, Peter Zijlstra wrote:
> > > On Thu, Aug 11, 2022 at 11:15:22AM +0200, Jiri Olsa wrote:
> > > > Keeping the resolved 'addr' in kallsyms_callback, instead of taking
> > > > ftrace_location value, because we depend on symbol address in the
> > > > cookie related code.
> > > >
> > > > With CONFIG_X86_KERNEL_IBT option the ftrace_location value differs
> > > > from symbol address, which screwes the symbol address cookies matching.
> > > >
> > > > There are 2 users of this function:
> > > > - bpf_kprobe_multi_link_attach
> > > > for which this fix is for
> > >
> > > Except you fail to explain what the problem is and how this helps
> > > anything.
> >
> > we search this array of resolved addresses later in cookie code
> > (bpf_kprobe_multi_cookie) for address returned by fprobe, which
> > is not 'ftrace_location' address
>
> What is fprobe?
https://lore.kernel.org/bpf/164800288611.1716332.7053663723617614668.stgit@devnote2/
>
> > so we want ftrace_lookup_symbols to return 'only' resolved address
> > at this point, not 'ftrace_location' address
>
> In general; I'm completely confused what any of this code is doing.
> Mostly I don't speak BPF *at*all*. And have very little clue as to what
> things are supposed to do, please help me along.
>
> But the thing is, we're likely going to change all this (function call
> abi) again in the very near future; it would be very nice if all this
> code could grow some what/why comments, because I've gotten lost
> multiple times in all this.
is there any outline of the change? is this the change in your x86/fineibt
branch that you brought up in the other thread?
jirka
next prev parent reply other threads:[~2022-08-16 8:41 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-11 9:15 [PATCHv2 bpf-next 0/6] bpf: Fixes for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 1/6] kprobes: Add new KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag Jiri Olsa
2022-08-15 9:57 ` Peter Zijlstra
2022-08-15 10:10 ` Jiri Olsa
2022-08-15 12:40 ` Peter Zijlstra
2022-08-16 7:01 ` Jiri Olsa
2022-08-30 15:08 ` Jiri Olsa
2022-09-08 8:26 ` Jiri Olsa
2022-09-08 12:01 ` Masami Hiramatsu
2022-08-11 9:15 ` [PATCHv2 bpf-next 2/6] ftrace: Keep the resolved addr in kallsyms_callback Jiri Olsa
2022-08-15 10:13 ` Peter Zijlstra
2022-08-15 10:30 ` Jiri Olsa
2022-08-15 12:45 ` Peter Zijlstra
2022-08-16 7:06 ` Jiri Olsa [this message]
2022-09-08 12:35 ` Masami Hiramatsu
2022-09-08 19:41 ` Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 3/6] bpf: Use given function address for trampoline ip arg Jiri Olsa
2022-08-15 10:18 ` Peter Zijlstra
2022-08-15 10:57 ` Jiri Olsa
2022-08-15 12:51 ` Peter Zijlstra
2022-08-17 13:40 ` Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 4/6] bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 5/6] bpf: Return value in kprobe get_func_ip only for entry address Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 6/6] selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-16 3:25 ` Andrii Nakryiko
2022-08-16 7:00 ` Jiri Olsa
2022-08-16 10:18 ` Jiri Olsa
2022-08-16 17:28 ` Andrii Nakryiko
2022-08-16 17:19 ` Andrii Nakryiko
2022-08-16 3:27 ` [PATCHv2 bpf-next 0/6] bpf: Fixes " Andrii Nakryiko
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