Re: [PATCH v3 bpf-next 3/9] selftests/bpf: add __ksym extern selftest

Validate libbpf is able to handle weak and strong kernel symbol externs in BPF
code correctly.

Signed-off-by: Andrii Nakryiko <redacted>
---
 .../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