selftests/bpf: Test subskeleton functionality

This patch changes the selftests/bpf Makefile to also generate
a subskel.h for every skel.h it would have normally generated.

Separately, it also introduces a new subskeleton test which tests
library objects, externs, weak symbols, kconfigs, and user maps.

Signed-off-by: Delyan Kratunov <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/.gitignore

···
 test_sysctl
 xdping
 test_cpp
+*.subskel.h
 *.skel.h
 *.lskel.h
 /no_alu32

tools/testing/selftests/bpf/Makefile

···
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
 
 LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
-		linked_vars.skel.h linked_maps.skel.h
+		linked_vars.skel.h linked_maps.skel.h 			\
+		test_subskeleton.skel.h test_subskeleton_lib.skel.h
+
+# In the subskeleton case, we want the test_subskeleton_lib.subskel.h file
+# but that's created as a side-effect of the skel.h generation.
+test_subskeleton.skel.h-deps := test_subskeleton_lib2.o test_subskeleton_lib.o test_subskeleton.o
+test_subskeleton_lib.skel.h-deps := test_subskeleton_lib2.o test_subskeleton_lib.o
 
 LSKELS := kfunc_call_test.c fentry_test.c fexit_test.c fexit_sleep.c \
 	test_ringbuf.c atomics.c trace_printk.c trace_vprintk.c \
···
 	$(Q)$$(BPFTOOL) gen object $$(<:.o=.linked3.o) $$(<:.o=.linked2.o)
 	$(Q)diff $$(<:.o=.linked2.o) $$(<:.o=.linked3.o)
 	$(Q)$$(BPFTOOL) gen skeleton $$(<:.o=.linked3.o) name $$(notdir $$(<:.o=)) > $$@
+	$(Q)$$(BPFTOOL) gen subskeleton $$(<:.o=.linked3.o) name $$(notdir $$(<:.o=)) > $$(@:.skel.h=.subskel.h)
 
 $(TRUNNER_BPF_LSKELS): %.lskel.h: %.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
 	$$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
···
 	$(Q)diff $$(@:.skel.h=.linked2.o) $$(@:.skel.h=.linked3.o)
 	$$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
 	$(Q)$$(BPFTOOL) gen skeleton $$(@:.skel.h=.linked3.o) name $$(notdir $$(@:.skel.h=)) > $$@
+	$(Q)$$(BPFTOOL) gen subskeleton $$(@:.skel.h=.linked3.o) name $$(notdir $$(@:.skel.h=)) > $$(@:.skel.h=.subskel.h)
 endif
 
 # ensure we set up tests.h header generation rule just once
···
 EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)	\
 	prog_tests/tests.h map_tests/tests.h verifier/tests.h		\
 	feature bpftool							\
-	$(addprefix $(OUTPUT)/,*.o *.skel.h *.lskel.h no_alu32 bpf_gcc bpf_testmod.ko)
+	$(addprefix $(OUTPUT)/,*.o *.skel.h *.lskel.h *.subskel.h no_alu32 bpf_gcc bpf_testmod.ko)
 
 .PHONY: docs docs-clean

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include "test_subskeleton.skel.h"
+#include "test_subskeleton_lib.subskel.h"
+
+static void subskeleton_lib_setup(struct bpf_object *obj)
+{
+	struct test_subskeleton_lib *lib = test_subskeleton_lib__open(obj);
+
+	if (!ASSERT_OK_PTR(lib, "open subskeleton"))
+		return;
+
+	*lib->rodata.var1 = 1;
+	*lib->data.var2 = 2;
+	lib->bss.var3->var3_1 = 3;
+	lib->bss.var3->var3_2 = 4;
+
+	test_subskeleton_lib__destroy(lib);
+}
+
+static int subskeleton_lib_subresult(struct bpf_object *obj)
+{
+	struct test_subskeleton_lib *lib = test_subskeleton_lib__open(obj);
+	int result;
+
+	if (!ASSERT_OK_PTR(lib, "open subskeleton"))
+		return -EINVAL;
+
+	result = *lib->bss.libout1;
+	ASSERT_EQ(result, 1 + 2 + 3 + 4 + 5 + 6, "lib subresult");
+
+	ASSERT_OK_PTR(lib->progs.lib_perf_handler, "lib_perf_handler");
+	ASSERT_STREQ(bpf_program__name(lib->progs.lib_perf_handler),
+		     "lib_perf_handler", "program name");
+
+	ASSERT_OK_PTR(lib->maps.map1, "map1");
+	ASSERT_STREQ(bpf_map__name(lib->maps.map1), "map1", "map name");
+
+	ASSERT_EQ(*lib->data.var5, 5, "__weak var5");
+	ASSERT_EQ(*lib->data.var6, 6, "extern var6");
+	ASSERT_TRUE(*lib->kconfig.CONFIG_BPF_SYSCALL, "CONFIG_BPF_SYSCALL");
+
+	test_subskeleton_lib__destroy(lib);
+	return result;
+}
+
+void test_subskeleton(void)
+{
+	int err, result;
+	struct test_subskeleton *skel;
+
+	skel = test_subskeleton__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	skel->rodata->rovar1 = 10;
+	skel->rodata->var1 = 1;
+	subskeleton_lib_setup(skel->obj);
+
+	err = test_subskeleton__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	err = test_subskeleton__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	/* trigger tracepoint */
+	usleep(1);
+
+	result = subskeleton_lib_subresult(skel->obj) * 10;
+	ASSERT_EQ(skel->bss->out1, result, "unexpected calculation");
+
+cleanup:
+	test_subskeleton__destroy(skel);
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) Meta Platforms, Inc. and affiliates. */
+
+#include <stdbool.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+/* volatile to force a read, compiler may assume 0 otherwise */
+const volatile int rovar1;
+int out1;
+
+/* Override weak symbol in test_subskeleton_lib */
+int var5 = 5;
+
+extern volatile bool CONFIG_BPF_SYSCALL __kconfig;
+
+extern int lib_routine(void);
+
+SEC("raw_tp/sys_enter")
+int handler1(const void *ctx)
+{
+	(void) CONFIG_BPF_SYSCALL;
+
+	out1 = lib_routine() * rovar1;
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) Meta Platforms, Inc. and affiliates. */
+
+#include <stdbool.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+/* volatile to force a read */
+const volatile int var1;
+volatile int var2 = 1;
+struct {
+	int var3_1;
+	__s64 var3_2;
+} var3;
+int libout1;
+
+extern volatile bool CONFIG_BPF_SYSCALL __kconfig;
+
+int var4[4];
+
+__weak int var5 SEC(".data");
+
+/* Fully contained within library extern-and-definition */
+extern int var6;
+
+int var7 SEC(".data.custom");
+
+int (*fn_ptr)(void);
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(max_entries, 16);
+} map1 SEC(".maps");
+
+extern struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(max_entries, 16);
+} map2 SEC(".maps");
+
+int lib_routine(void)
+{
+	__u32 key = 1, value = 2;
+
+	(void) CONFIG_BPF_SYSCALL;
+	bpf_map_update_elem(&map2, &key, &value, BPF_ANY);
+
+	libout1 = var1 + var2 + var3.var3_1 + var3.var3_2 + var5 + var6;
+	return libout1;
+}
+
+SEC("perf_event")
+int lib_perf_handler(struct pt_regs *ctx)
+{
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/test_subskeleton_lib2.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+int var6 = 6;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(max_entries, 16);
+} map2 SEC(".maps");
+
+char LICENSE[] SEC("license") = "GPL";