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Date:   Fri, 19 Jun 2020 18:09:06 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Kernel Team <kernel-team@...com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Song Liu <songliubraving@...com>,
        Quentin Monnet <quentin@...valent.com>
Subject: Re: [PATCH v3 bpf-next 3/9] selftests/bpf: add __ksym extern selftest

Reviewed-by: Hao Luo <haoluo@...gle.com>


On Fri, Jun 19, 2020 at 4:19 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Validate libbpf is able to handle weak and strong kernel symbol externs in BPF
> code correctly.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  .../testing/selftests/bpf/prog_tests/ksyms.c  | 71 +++++++++++++++++++
>  .../testing/selftests/bpf/progs/test_ksyms.c  | 32 +++++++++
>  2 files changed, 103 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms.c b/tools/testing/selftests/bpf/prog_tests/ksyms.c
> new file mode 100644
> index 000000000000..e3d6777226a8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/ksyms.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2019 Facebook */
> +
> +#include <test_progs.h>
> +#include "test_ksyms.skel.h"
> +#include <sys/stat.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;
> +
> +       while (fscanf(f, "%llx %c %499s%*[^\n]\n", &addr, &type, name) > 0) {
> +               if (strcmp(name, sym) == 0) {
> +                       res = addr;
> +                       goto out;
> +               }
> +       }
> +
> +       CHECK(false, "not_found", "symbol %s not found\n", sym);
> +out:
> +       fclose(f);
> +       return res;
> +}
> +
> +void test_ksyms(void)
> +{
> +       __u64 link_fops_addr = kallsyms_find("bpf_link_fops");
> +       const char *btf_path = "/sys/kernel/btf/vmlinux";
> +       struct test_ksyms *skel;
> +       struct test_ksyms__data *data;
> +       struct stat st;
> +       __u64 btf_size;
> +       int err;
> +
> +       if (CHECK(stat(btf_path, &st), "stat_btf", "err %d\n", errno))
> +               return;
> +       btf_size = st.st_size;
> +
> +       skel = test_ksyms__open_and_load();
> +       if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
> +               return;
> +
> +       err = test_ksyms__attach(skel);
> +       if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
> +               goto cleanup;
> +
> +       /* trigger tracepoint */
> +       usleep(1);
> +
> +       data = skel->data;
> +       CHECK(data->out__bpf_link_fops != link_fops_addr, "bpf_link_fops",
> +             "got 0x%llx, exp 0x%llx\n",
> +             data->out__bpf_link_fops, link_fops_addr);
> +       CHECK(data->out__bpf_link_fops1 != 0, "bpf_link_fops1",
> +             "got %llu, exp %llu\n", data->out__bpf_link_fops1, (__u64)0);
> +       CHECK(data->out__btf_size != btf_size, "btf_size",
> +             "got %llu, exp %llu\n", data->out__btf_size, btf_size);
> +       CHECK(data->out__per_cpu_start != 0, "__per_cpu_start",
> +             "got %llu, exp %llu\n", data->out__per_cpu_start, (__u64)0);
> +
> +cleanup:
> +       test_ksyms__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_ksyms.c b/tools/testing/selftests/bpf/progs/test_ksyms.c
> new file mode 100644
> index 000000000000..6c9cbb5a3bdf
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_ksyms.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2019 Facebook */
> +
> +#include <stdbool.h>
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +__u64 out__bpf_link_fops = -1;
> +__u64 out__bpf_link_fops1 = -1;
> +__u64 out__btf_size = -1;
> +__u64 out__per_cpu_start = -1;
> +
> +extern const void bpf_link_fops __ksym;
> +extern const void __start_BTF __ksym;
> +extern const void __stop_BTF __ksym;
> +extern const void __per_cpu_start __ksym;
> +/* non-existing symbol, weak, default to zero */
> +extern const void bpf_link_fops1 __ksym __weak;
> +
> +SEC("raw_tp/sys_enter")
> +int handler(const void *ctx)
> +{
> +       out__bpf_link_fops = (__u64)&bpf_link_fops;
> +       out__btf_size = (__u64)(&__stop_BTF - &__start_BTF);
> +       out__per_cpu_start = (__u64)&__per_cpu_start;
> +
> +       out__bpf_link_fops1 = (__u64)&bpf_link_fops1;
> +
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.24.1
>

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