selftests/bpf: Test auto-load disabling logic for BPF programs

Validate that BPF object with broken (in multiple ways) BPF program can still
be successfully loaded, if that broken BPF program is disabled.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200625232629.3444003-3-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/autoload.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include <test_progs.h>
+#include <time.h>
+#include "test_autoload.skel.h"
+
+void test_autoload(void)
+{
+	int duration = 0, err;
+	struct test_autoload* skel;
+
+	skel = test_autoload__open_and_load();
+	/* prog3 should be broken */
+	if (CHECK(skel, "skel_open_and_load", "unexpected success\n"))
+		goto cleanup;
+
+	skel = test_autoload__open();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		goto cleanup;
+
+	/* don't load prog3 */
+	bpf_program__set_autoload(skel->progs.prog3, false);
+
+	err = test_autoload__load(skel);
+	if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
+		goto cleanup;
+
+	err = test_autoload__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	usleep(1);
+
+	CHECK(!skel->bss->prog1_called, "prog1", "not called\n");
+	CHECK(!skel->bss->prog2_called, "prog2", "not called\n");
+	CHECK(skel->bss->prog3_called, "prog3", "called?!\n");
+
+cleanup:
+	test_autoload__destroy(skel);
+}

tools/testing/selftests/bpf/progs/test_autoload.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
+
+bool prog1_called = false;
+bool prog2_called = false;
+bool prog3_called = false;
+
+SEC("raw_tp/sys_enter")
+int prog1(const void *ctx)
+{
+	prog1_called = true;
+	return 0;
+}
+
+SEC("raw_tp/sys_exit")
+int prog2(const void *ctx)
+{
+	prog2_called = true;
+	return 0;
+}
+
+struct fake_kernel_struct {
+	int whatever;
+} __attribute__((preserve_access_index));
+
+SEC("fentry/unexisting-kprobe-will-fail-if-loaded")
+int prog3(const void *ctx)
+{
+	struct fake_kernel_struct *fake = (void *)ctx;
+	fake->whatever = 123;
+	prog3_called = true;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";