selftests/bpf: Add multi-file statically linked BPF object file test

Add Makefile infra to specify multi-file BPF object files (and derivative
skeletons). Add first selftest validating BPF static linker can merge together
successfully two independent BPF object files and resulting object and
skeleton are correct and usable.

Use the same F(F(F(X))) = F(F(X)) identity test on linked object files as for
the case of single BPF object files.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-13-andrii@kernel.org

1 files changed, 30 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_static_linked1.c b/tools/testing/selftests/bpf/progs/test_static_linked1.c
new file mode 100644
index 000000000000..ea1a6c4c7172
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_static_linked1.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+/* 8-byte aligned .bss */
+static volatile long static_var1;
+static volatile int static_var11;
+int var1 = 0;
+/* 4-byte aligned .rodata */
+const volatile int rovar1;
+
+/* same "subprog" name in both files */
+static __noinline int subprog(int x)
+{
+	/* but different formula */
+	return x * 2;
+}
+
+SEC("raw_tp/sys_enter")
+int handler1(const void *ctx)
+{
+	var1 = subprog(rovar1) + static_var1 + static_var11;
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
+int VERSION SEC("version") = 1;