Hi!
On Fri, 2020-06-19 at 16:16 -0700, Andrii Nakryiko wrote:
> Validate libbpf is able to handle weak and strong kernel symbol
> externs in BPF
> code correctly.
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> ---
> .../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);
> +}
Why is __per_cpu_start expected to be 0? On my x86_64 Debian VM it is
something like ffffffffxxxxxxxx, and this test fails. Wouldn't
it be better to take the value from kallsyms, like it's done with
bpf_link_fops, or am I missing something in my setup?
Best regards,
Ilya
