From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yaniv Agman <yanivagman@gmail.com>
Cc: bpf <bpf@vger.kernel.org>
Subject: Re: libbpf: Loading kprobes fail on some distros
Date: Mon, 12 Oct 2020 15:10:59 -0700 [thread overview]
Message-ID: <CAEf4BzZAuXNBA2Z309=zPSf=MHLfzWTWeK_8tXGZ0+-bPkZKAQ@mail.gmail.com> (raw)
In-Reply-To: <CAMy7=ZUcdu7_nxnUyGZkGyue5rG_0YRMXqhrnvfKW64dio1LpQ@mail.gmail.com>
On Mon, Oct 12, 2020 at 2:21 PM Yaniv Agman <yanivagman@gmail.com> wrote:
>
> בתאריך יום ב׳, 12 באוק׳ 2020 ב-20:02 מאת Andrii Nakryiko
> <andrii.nakryiko@gmail.com>:
> >
> > On Sun, Oct 11, 2020 at 7:10 PM Yaniv Agman <yanivagman@gmail.com> wrote:
> > >
> > > Trying to load kprobes on ubuntu 4.15.0, I get the following error:
> > > libbpf: load bpf program failed: Invalid argument
> > >
> > > The same kprobes load successfully using bcc
> > >
> > > After some digging, I found that the issue was with the kernel version
> > > given to the bpf syscall. While libbpf calculated the value 265984 for
> > > the kern_version argument, bcc used 266002.
> > > It turns out that some distros (e.g. ubuntu, debian) change the patch
> > > number of the kernel version, as detailed in:
> > > https://github.com/ajor/bpftrace/issues/8
> > >
> > > I didn't find a proper API in libbpf to load kprobes in such cases -
> > > is there any?
> >
> > Yes, you can override kernel version that libbpf determines from
> > utsname with a special variable in your BPF code:
> >
> > int KERNEL_VERSION SEC("version") = 123;
>
> Thanks! This is trivial, I should have thought about it myself.
> For some reason, I thought that the loader should handle that, but if I include
libbpf does handle that automatically, but it has to get the kernel
version from utsname() call, which apparently doesn't always match
what kernel believes LINUX_VERSION_CODE is.
> int KERNEL_VERSION SEC("version") = LINUX_VERSION_CODE;
> It should just work
>
> Thanks again!
prev parent reply other threads:[~2020-10-12 22:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-11 19:28 libbpf: Loading kprobes fail on some distros Yaniv Agman
2020-10-12 17:01 ` Andrii Nakryiko
2020-10-12 21:20 ` Yaniv Agman
2020-10-12 22:10 ` Andrii Nakryiko [this message]
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