Merge branch 'bpftool-show-pid'

Andrii Nakryiko says:

====================
This patch set implements libbpf support for a second kind of special externs,
kernel symbols, in addition to existing Kconfig externs.

Right now, only untyped (const void) externs are supported, which, in
C language, allow only to take their address. In the future, with kernel BTF
getting type info about its own global and per-cpu variables, libbpf will
extend this support with BTF type info, which will allow to also directly
access variable's contents and follow its internal pointers, similarly to how
it's possible today in fentry/fexit programs.

As a first practical use of this functionality, bpftool gained ability to show
PIDs of processes that have open file descriptors for BPF map/program/link/BTF
object. It relies on iter/task_file BPF iterator program to extract this
information efficiently.

There was a bunch of bpftool refactoring (especially Makefile) necessary to
generalize bpftool's internal BPF program use. This includes generalization of
BPF skeletons support, addition of a vmlinux.h generation, extracting and
building minimal subset of bpftool for bootstrapping.

v2->v3:
- fix sec_btf_id check (Hao);

v1->v2:
- docs fixes (Quentin);
- dual GPL/BSD license for pid_inter.bpf.c (Quentin);
- NULL-init kcfg_data (Hao Luo);

rfc->v1:
- show pids, if supported by kernel, always (Alexei);
- switched iter output to binary to support showing process names;
- update man pages;
- fix few minor bugs in libbpf w.r.t. extern iteration.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 103 insertions, 0 deletions

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";