From: Alexei Starovoitov <ast@plumgrid•com>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi•com>
Cc: Ingo Molnar <mingo@kernel•org>,
Steven Rostedt <rostedt@goodmis•org>,
Namhyung Kim <namhyung@kernel•org>,
Arnaldo Carvalho de Melo <acme@infradead•org>,
Jiri Olsa <jolsa@redhat•com>,
"David S. Miller" <davem@davemloft•net>,
Daniel Borkmann <daniel@iogearbox•net>,
Peter Zijlstra <a.p.zijlstra@chello•nl>,
linux-api@vger•kernel.org, netdev@vger•kernel.org,
linux-kernel@vger•kernel.org
Subject: Re: [PATCH v9 tip 3/9] tracing: attach BPF programs to kprobes
Date: Sun, 22 Mar 2015 11:03:46 -0700 [thread overview]
Message-ID: <550F0402.80900@plumgrid.com> (raw)
In-Reply-To: <550E9421.7030507@hitachi.com>
On 3/22/15 3:06 AM, Masami Hiramatsu wrote:
> (2015/03/22 1:02), Alexei Starovoitov wrote:
>> On 3/21/15 5:14 AM, Masami Hiramatsu wrote:
>>> (2015/03/21 8:30), Alexei Starovoitov wrote:
>>>>
>>>> Note, kprobes are _not_ a stable kernel ABI, so bpf programs attached to
>>>> kprobes must be recompiled for every kernel version and user must supply correct
>>>> LINUX_VERSION_CODE in attr.kern_version during bpf_prog_load() call.
>>>>
>>>
>>> Would you mean that the ABI of kprobe-based BPF programs? Kprobe API/ABIs
>>> (register_kprobe() etc.) are stable, but the code who use kprobes certainly
>>> depends the kernel binary by design. So, if you meant it, BPF programs must
>>> be recompiled for every kernel binaries (including configuration changes,
>>> not only its version).
>>
>> yes. I mainly meant that bpf+kprobe programs must be recompiled
>> for every kernel binary.
>
> Hmm, if so, as we do in perf (and systemtap too), you'd better check
> kernel's build-id instead of the kernel version when loading the
> BPF program. It is safer than the KERNEL_VERSION_CODE.
It's not about safety. As I mentioned in cover letter:
"version check is not used for safety, but for enforcing 'non-ABI-ness'"
In other words it's like check-box next to 'terms and conditions'
paragraph that the user has to click before he can continue.
By providing 'kern_version' during loading the user accepts the fact
that bpf+kprobe is not a stable ABI. Nothing more and nothing less.
build-id cannot achieve that, because it cannot be checked from inside
the kernel.
User space tools that will compile ktap/dtrace scripts into bpf might
use build-id for their own purpose, but that's a different discussion.
next prev parent reply other threads:[~2015-03-22 18:03 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-20 23:30 [PATCH v9 tip 0/9] tracing: attach eBPF programs to kprobes Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 1/9] bpf: make internal bpf API independent of CONFIG_BPF_SYSCALL ifdefs Alexei Starovoitov
2015-03-21 12:16 ` Masami Hiramatsu
2015-03-20 23:30 ` [PATCH v9 tip 2/9] tracing: add kprobe flag Alexei Starovoitov
[not found] ` <1426894210-27441-3-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-21 12:16 ` Masami Hiramatsu
2015-03-20 23:30 ` [PATCH v9 tip 3/9] tracing: attach BPF programs to kprobes Alexei Starovoitov
[not found] ` <1426894210-27441-4-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-21 12:14 ` Masami Hiramatsu
2015-03-21 16:02 ` Alexei Starovoitov
[not found] ` <550D962E.7010400-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-22 10:06 ` Masami Hiramatsu
2015-03-22 18:03 ` Alexei Starovoitov [this message]
[not found] ` <550F0402.80900-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-23 2:17 ` Masami Hiramatsu
2015-03-23 4:57 ` bpf+tracing next steps. Was: " Alexei Starovoitov
[not found] ` <550F9D20.7070006-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-23 9:27 ` Masami Hiramatsu
2015-03-25 0:40 ` Alexei Starovoitov
[not found] ` <5512040B.3020605-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-25 12:07 ` Masami Hiramatsu
[not found] ` <1426894210-27441-1-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-20 23:30 ` [PATCH v9 tip 4/9] tracing: allow BPF programs to call bpf_ktime_get_ns() Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 5/9] tracing: allow BPF programs to call bpf_trace_printk() Alexei Starovoitov
[not found] ` <1426894210-27441-6-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-22 11:10 ` Ingo Molnar
[not found] ` <20150322111040.GA18695-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-03-22 18:05 ` Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 9/9] samples: bpf: kmem_alloc/free tracker Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 6/9] samples: bpf: simple non-portable kprobe filter example Alexei Starovoitov
[not found] ` <1426894210-27441-7-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-23 7:29 ` Ingo Molnar
[not found] ` <20150323072929.GB25184-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-03-23 17:23 ` Alexei Starovoitov
2015-03-23 7:35 ` Ingo Molnar
[not found] ` <20150323073506.GC25184-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-03-23 17:32 ` Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 7/9] samples: bpf: counting example for kfree_skb and write syscall Alexei Starovoitov
2015-03-20 23:30 ` [PATCH v9 tip 8/9] samples: bpf: IO latency analysis (iosnoop/heatmap) Alexei Starovoitov
2015-03-23 7:40 ` Ingo Molnar
2015-03-23 17:41 ` Alexei Starovoitov
2015-03-21 4:08 ` [PATCH v9 tip 0/9] tracing: attach eBPF programs to kprobes Steven Rostedt
[not found] ` <20150321000812.606ef8cb-2kNGR76GQU9OHLTnHDQRgA@public.gmane.org>
2015-03-23 7:36 ` Ingo Molnar
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