netdev - Re: [PATCH v2 2/2] samples, selftests/bpf: add NULL check for ksym

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Date:   Fri, 29 Mar 2019 11:54:03 +0900
From:   "Daniel T. Lee" <danieltimlee@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/2] samples, selftests/bpf: add NULL check for ksym_search

I'm aware that I didn't cover the "spintest_user.c".
Because, spintest sample isn't running currently since there is no
such symbol called 'spin_lock'.

At "spintest_kern.c", it has 'kprobe/spin_lock' and
'kprobe/spin_unlock' and some
others kernel symbols like below.

SEC("kprobe/spin_unlock")PROG(p1)
SEC("kprobe/spin_lock")PROG(p2)
SEC("kprobe/mutex_spin_on_owner")PROG(p3)
SEC("kprobe/rwsem_spin_on_owner")PROG(p4)
SEC("kprobe/spin_unlock_irqrestore")PROG(p5)
SEC("kprobe/_raw_spin_unlock_irqrestore")PROG(p6)
SEC("kprobe/_raw_spin_unlock_bh")PROG(p7)
SEC("kprobe/_raw_spin_unlock")PROG(p8)
SEC("kprobe/_raw_spin_lock_irqsave")PROG(p9)
....

But the thing is, 'spin_lock' kernel symbol won't exist, as it has
been __always_inline'd
at commit 349056 at Jul,13,2015.

https://cregit.linuxsources.org/code/4.20/include/linux/spinlock.h.html#327

$ uname -r
5.0.0+
$ grep "spin_lock" /proc/kallsyms
0000000000000000 T queued_spin_lock_slowpath
0000000000000000 t process_spin_lock
0000000000000000 T bpf_spin_lock
0000000000000000 T btf_find_spin_lock
0000000000000000 T _raw_spin_lock_bh
0000000000000000 T _raw_spin_lock_irqsave
0000000000000000 T _raw_spin_lock
0000000000000000 T _raw_spin_lock_irq
...

I'm pretty sure there is something I don't know due to my lack of skills.
Is there any way to run this sample without having such kernel symbol?

On Fri, Mar 29, 2019 at 1:30 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 03/27/2019 03:45 PM, Daniel T. Lee wrote:
> > Since, ksym_search added with verification logic for symbols existence,
> > it could return NULL when the kernel symbols are not loaded.
> >
> > This commit will add NULL check logic after ksym_search.
> >
> > Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> > ---
> > Changes in v2:
> >     - Added NULL check for selftests/bpf/prog_tests/get_stack_raw_tp.c
> >
> >  samples/bpf/offwaketime_user.c                            | 5 +++++
> >  samples/bpf/sampleip_user.c                               | 5 +++++
> >  samples/bpf/trace_event_user.c                            | 5 +++++
> >  tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c | 4 ++--
> >  4 files changed, 17 insertions(+), 2 deletions(-)
>
> Still not all occurrences from samples covered:
>
> $ git grep -n ksym_search samples/bpf/
> samples/bpf/offwaketime_user.c:30:      sym = ksym_search(addr);
> samples/bpf/sampleip_user.c:111:                        sym = ksym_search(counts[i].ip);
> samples/bpf/spintest_user.c:39:                 sym = ksym_search(value);
> samples/bpf/trace_event_user.c:36:      sym = ksym_search(addr);