selftests/bpf: Add global subprog context passing tests

Add tests validating that it's possible to pass context arguments into
global subprogs for various types of programs, including a particularly
tricky KPROBE programs (which cover kprobes, uprobes, USDTs, a vast and
important class of programs).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230216045954.3002473-4-andrii@kernel.org

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

@@ -18,6 +18,7 @@
 #include "test_global_func15.skel.h"
 #include "test_global_func16.skel.h"
 #include "test_global_func17.skel.h"
+#include "test_global_func_ctx_args.skel.h"
 
 void test_test_global_funcs(void)
 {
@@ -38,4 +39,5 @@ void test_test_global_funcs(void)
 	RUN_TESTS(test_global_func15);
 	RUN_TESTS(test_global_func16);
 	RUN_TESTS(test_global_func17);
+	RUN_TESTS(test_global_func_ctx_args);
 }

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

@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+static long stack[256];
+
+/*
+ * KPROBE contexts
+ */
+
+__weak int kprobe_typedef_ctx_subprog(bpf_user_pt_regs_t *ctx)
+{
+	return bpf_get_stack(ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?kprobe")
+__success
+int kprobe_typedef_ctx(void *ctx)
+{
+	return kprobe_typedef_ctx_subprog(ctx);
+}
+
+#define pt_regs_struct_t typeof(*(__PT_REGS_CAST((struct pt_regs *)NULL)))
+
+__weak int kprobe_struct_ctx_subprog(pt_regs_struct_t *ctx)
+{
+	return bpf_get_stack((void *)ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?kprobe")
+__success
+int kprobe_resolved_ctx(void *ctx)
+{
+	return kprobe_struct_ctx_subprog(ctx);
+}
+
+/* this is current hack to make this work on old kernels */
+struct bpf_user_pt_regs_t {};
+
+__weak int kprobe_workaround_ctx_subprog(struct bpf_user_pt_regs_t *ctx)
+{
+	return bpf_get_stack(ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?kprobe")
+__success
+int kprobe_workaround_ctx(void *ctx)
+{
+	return kprobe_workaround_ctx_subprog(ctx);
+}
+
+/*
+ * RAW_TRACEPOINT contexts
+ */
+
+__weak int raw_tp_ctx_subprog(struct bpf_raw_tracepoint_args *ctx)
+{
+	return bpf_get_stack(ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?raw_tp")
+__success
+int raw_tp_ctx(void *ctx)
+{
+	return raw_tp_ctx_subprog(ctx);
+}
+
+/*
+ * RAW_TRACEPOINT_WRITABLE contexts
+ */
+
+__weak int raw_tp_writable_ctx_subprog(struct bpf_raw_tracepoint_args *ctx)
+{
+	return bpf_get_stack(ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?raw_tp")
+__success
+int raw_tp_writable_ctx(void *ctx)
+{
+	return raw_tp_writable_ctx_subprog(ctx);
+}
+
+/*
+ * PERF_EVENT contexts
+ */
+
+__weak int perf_event_ctx_subprog(struct bpf_perf_event_data *ctx)
+{
+	return bpf_get_stack(ctx, &stack, sizeof(stack), 0);
+}
+
+SEC("?perf_event")
+__success
+int perf_event_ctx(void *ctx)
+{
+	return perf_event_ctx_subprog(ctx);
+}