On Wed, Jul 15, 2020 at 2:46 PM Hao Luo haoluo@google.com wrote:
Extend ksyms.c selftest to make sure BTF enables direct loads of ksyms.
Note that test is done against the kernel btf extended with kernel VARs.
Signed-off-by: Hao Luo haoluo@google.com
tools/testing/selftests/bpf/prog_tests/ksyms.c | 2 ++ tools/testing/selftests/bpf/progs/test_ksyms.c | 14 ++++++++++++++ 2 files changed, 16 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms.c b/tools/testing/selftests/bpf/prog_tests/ksyms.c index e3d6777226a8..0e7f3bc3b0ae 100644 --- a/tools/testing/selftests/bpf/prog_tests/ksyms.c +++ b/tools/testing/selftests/bpf/prog_tests/ksyms.c @@ -65,6 +65,8 @@ void test_ksyms(void) "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);
CHECK(data->out__rq_cpu != 0, "rq_cpu","got %llu, exp %llu\n", data->out__rq_cpu, (__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 index 6c9cbb5a3bdf..e777603757e5 100644 --- a/tools/testing/selftests/bpf/progs/test_ksyms.c +++ b/tools/testing/selftests/bpf/progs/test_ksyms.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2019 Facebook */
+#include "vmlinux.h" #include <stdbool.h> #include <linux/bpf.h> #include <bpf/bpf_helpers.h> @@ -9,11 +10,13 @@ __u64 out__bpf_link_fops = -1; __u64 out__bpf_link_fops1 = -1; __u64 out__btf_size = -1; __u64 out__per_cpu_start = -1; +__u64 out__rq_cpu = -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; +extern const void runqueues __ksym;
This should ideally look like a real global variable extern:
extern const struct rq runqueues __ksym;
But that's the case for non-per-cpu variables. You didn't seem to address per-CPU variables in this patch set. How did you intend to handle that? We should look at a possible BPF helper to access such variables as well and how the verifier will prevent direct memory accesses for such variables.
We should have some BPF helper that accepts per-CPU PTR_TO_BTF_ID, and returns PTR_TO_BTF_ID, but adjusted to desired CPU. And verifier ideally would allow direct memory access on that resulting PTR_TO_BTF_ID, but not on per-CPU one. Not sure yet how this should look like, but the verifier probably needs to know that variable itself is per-cpu, no?
/* non-existing symbol, weak, default to zero */ extern const void bpf_link_fops1 __ksym __weak;
@@ -29,4 +32,15 @@ int handler(const void *ctx) return 0; }
+SEC("tp_btf/sys_enter") +int handler_tp_btf(const void *ctx) +{
const struct rq *rq = &runqueues;/* rq now points to the runqueue of cpu 0. */out__rq_cpu = rq->cpu;return 0;+}
char _license[] SEC("license") = "GPL";
2.27.0.389.gc38d7665816-goog