Re: [PATCH bpf-next v1 5/8] bpf/selftests: ksyms_btf to test typed ksyms

[Yonghong Song <yhs@fb.com>]

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@google.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.

> +
> +	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_btf(void)
> +{
> +	__u64 runqueues_addr = kallsyms_find("runqueues");
> +	__u64 bpf_prog_active_addr = kallsyms_find("bpf_prog_active");
> +	struct test_ksyms_btf *skel;
> +	struct test_ksyms_btf__data *data;
> +	struct btf *btf;
> +	int percpu_datasec;
> +	int err;
> +
> +	btf = libbpf_find_kernel_btf();
> +	if (CHECK(IS_ERR(btf), "btf_exists", "failed to load kernel BTF: %ld\n",
> +		  PTR_ERR(btf)))
> +		return;
> +
> +	percpu_datasec = btf__find_by_name_kind(btf, ".data..percpu",
> +						BTF_KIND_DATASEC);
> +	if (percpu_datasec < 0) {
> +		printf("%s:SKIP:no PERCPU DATASEC in kernel btf\n",
> +		       __func__);
> +		test__skip();
> +		return;
> +	}
> +
> +	skel = test_ksyms_btf__open_and_load();
> +	if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
> +		return;
> +
> +	err = test_ksyms_btf__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__runqueues != runqueues_addr, "runqueues",
> +	      "got %llu, exp %llu\n", data->out__runqueues, runqueues_addr);
> +	CHECK(data->out__bpf_prog_active != bpf_prog_active_addr, "bpf_prog_active",
> +	      "got %llu, exp %llu\n", data->out__bpf_prog_active, bpf_prog_active_addr);
> +
> +cleanup:
> +	test_ksyms_btf__destroy(skel);
> +}
> 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;
> +
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
>