netdev - Re: [PATCH bpf-next v1 5/8] bpf/selftests: ksyms

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Date:   Fri, 21 Aug 2020 16:03:03 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Hao Luo <haoluo@...gle.com>, Networking <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Quentin Monnet <quentin@...valent.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Andrey Ignatov <rdna@...com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [PATCH bpf-next v1 5/8] bpf/selftests: ksyms_btf to test typed ksyms

On Thu, Aug 20, 2020 at 10:32 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 8/19/20 3:40 PM, Hao Luo wrote:
> > Selftests for typed ksyms. Tests two types of ksyms: one is a struct,
> > the other is a plain int. This tests two paths in the kernel. Struct
> > ksyms will be converted into PTR_TO_BTF_ID by the verifier while int
> > typed ksyms will be converted into PTR_TO_MEM.
> >
> > Signed-off-by: Hao Luo <haoluo@...gle.com>
> > ---
> >   .../selftests/bpf/prog_tests/ksyms_btf.c      | 77 +++++++++++++++++++
> >   .../selftests/bpf/progs/test_ksyms_btf.c      | 23 ++++++
> >   2 files changed, 100 insertions(+)
> >   create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> >   create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> > new file mode 100644
> > index 000000000000..1dad61ba7e99
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> > @@ -0,0 +1,77 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2020 Google */
> > +
> > +#include <test_progs.h>
> > +#include <bpf/libbpf.h>
> > +#include <bpf/btf.h>
> > +#include "test_ksyms_btf.skel.h"
> > +
> > +static int duration;
> > +
> > +static __u64 kallsyms_find(const char *sym)
> > +{
> > +     char type, name[500];
> > +     __u64 addr, res = 0;
> > +     FILE *f;
> > +
> > +     f = fopen("/proc/kallsyms", "r");
> > +     if (CHECK(!f, "kallsyms_fopen", "failed to open: %d\n", errno))
> > +             return 0;
>
> could you check whether libbpf API can provide this functionality for
> you? As far as I know, libbpf does parse /proc/kallsyms.

No need to use libbpf's implementation. We already have
kallsyms_find() in prog_tests/ksyms.c and a combination of
load_kallsyms() + ksym_get_addr() in trace_helpers.c. It would be good
to switch to one implementation for both prog_tests/ksyms.c and this
one.


>
> > +
> > +     while (fscanf(f, "%llx %c %499s%*[^\n]\n", &addr, &type, name) > 0) {
> > +             if (strcmp(name, sym) == 0) {
> > +                     res = addr;
> > +                     goto out;
> > +             }
> > +     }
> > +

[...]

> > diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_btf.c b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> > new file mode 100644
> > index 000000000000..e04e31117f84
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> > @@ -0,0 +1,23 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2020 Google */
> > +
> > +#include "vmlinux.h"
> > +
> > +#include <bpf/bpf_helpers.h>
> > +
> > +__u64 out__runqueues = -1;
> > +__u64 out__bpf_prog_active = -1;
> > +
> > +extern const struct rq runqueues __ksym; /* struct type global var. */
> > +extern const int bpf_prog_active __ksym; /* int type global var. */
> > +
> > +SEC("raw_tp/sys_enter")
> > +int handler(const void *ctx)
> > +{
> > +     out__runqueues = (__u64)&runqueues;
> > +     out__bpf_prog_active = (__u64)&bpf_prog_active;
> > +

You didn't test accessing any of the members of runqueues, because BTF
only has per-CPU variables, right? Adding global/static variables was
adding too much data to BTF or something like that, is that right?

> > +     return 0;
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> >