Add selftest validating various aspects of statically linking functions:
- no conflicts and correct resolution for name-conflicting static funcs;
- correct resolution of extern functions;
- correct handling of weak functions, both resolution itself and libbpf's
handling of unused weak function that "lost" (it leaves gaps in code with
no ELF symbols);
- correct handling of hidden visibility to turn global function into
"static" for the purpose of BPF verification.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/testing/selftests/bpf/Makefile | 3 +-
.../selftests/bpf/prog_tests/linked_funcs.c | 42 +++++++++++
.../selftests/bpf/progs/linked_funcs1.c | 73 +++++++++++++++++++
.../selftests/bpf/progs/linked_funcs2.c | 73 +++++++++++++++++++
4 files changed, 190 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c
create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c
create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index cfa3e91c9a49..c5d25aef1074 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -303,9 +303,10 @@ endef
SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
-LINKED_SKELS := test_static_linked.skel.h
+LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h
test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
+linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
diff --git a/tools/testing/selftests/bpf/prog_tests/linked_funcs.c b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
new file mode 100644
index 000000000000..768166a7c534
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <sys/syscall.h>
+#include "linked_funcs.skel.h"
+
+void test_linked_funcs(void)
+{
+ int err;
+ struct linked_funcs* skel;
+
+ skel = linked_funcs__open();
+ if (!ASSERT_OK_PTR(skel, "skel_open"))
+ return;
+
+ skel->rodata->my_tid = syscall(SYS_gettid);
+ skel->rodata->syscall_id = SYS_getpgid;
+
+ err = linked_funcs__load(skel);
+ if (!ASSERT_OK(err, "skel_load"))
+ goto cleanup;
+
+ err = linked_funcs__attach(skel);
+ if (!ASSERT_OK(err, "skel_attach"))
+ goto cleanup;
+
+ /* trigger */
+ syscall(SYS_getpgid);
+
+ ASSERT_EQ(skel->bss->output_val1, 2000 + 2000, "output_val1");
+ ASSERT_EQ(skel->bss->output_ctx1, SYS_getpgid, "output_ctx1");
+ ASSERT_EQ(skel->bss->output_weak1, 42, "output_weak1");
+
+ ASSERT_EQ(skel->bss->output_val2, 2 * 1000 + 2 * (2 * 1000), "output_val2");
+ ASSERT_EQ(skel->bss->output_ctx2, SYS_getpgid, "output_ctx2");
+ /* output_weak2 should never be updated */
+ ASSERT_EQ(skel->bss->output_weak2, 0, "output_weak2");
+
+cleanup:
+ linked_funcs__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/linked_funcs1.c b/tools/testing/selftests/bpf/progs/linked_funcs1.c
new file mode 100644
index 000000000000..cc621d4e4d82
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_funcs1.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* weak and shared between two files */
+const volatile int my_tid __weak = 0;
+const volatile long syscall_id __weak = 0;
+
+int output_val1 = 0;
+int output_ctx1 = 0;
+int output_weak1 = 0;
+
+/* same "subprog" name in all files, but it's ok because they all are static */
+static __noinline int subprog(int x)
+{
+ /* but different formula */
+ return x * 1;
+}
+
+/* Global functions can't be void */
+int set_output_val1(int x)
+{
+ output_val1 = x + subprog(x);
+ return x;
+}
+
+/* This function can't be verified as global, as it assumes raw_tp/sys_enter
+ * context and accesses syscall id (second argument). So we mark it as
+ * __hidden, so that libbpf will mark it as static in the final object file,
+ * right before verifying it in the kernel.
+ *
+ * But we don't mark it as __hidden here, rather at extern site. __hidden is
+ * "contaminating" visibility, so it will get propagated from either extern or
+ * actual definition (including from the losing __weak definition).
+ */
+void set_output_ctx1(__u64 *ctx)
+{
+ output_ctx1 = ctx[1]; /* long id, same as in BPF_PROG below */
+}
+
+/* this weak instance should win because it's the first one */
+__weak int set_output_weak(int x)
+{
+ output_weak1 = x;
+ return x;
+}
+
+extern int set_output_val2(int x);
+
+/* here we'll force set_output_ctx2() to be __hidden in the final obj file */
+__hidden extern void set_output_ctx2(__u64 *ctx);
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler1, struct pt_regs *regs, long id)
+{
+ if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
+ return 0;
+
+ set_output_val2(1000);
+ set_output_ctx2(ctx); /* ctx definition is hidden in BPF_PROG macro */
+
+ /* keep input value the same across both files to avoid dependency on
+ * handler call order; differentiate by output_weak1 vs output_weak2.
+ */
+ set_output_weak(42);
+
+ return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/linked_funcs2.c b/tools/testing/selftests/bpf/progs/linked_funcs2.c
new file mode 100644
index 000000000000..a5a935a4f748
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_funcs2.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* weak and shared between both files */
+const volatile int my_tid __weak = 0;
+const volatile long syscall_id __weak = 0;
+
+int output_val2 = 0;
+int output_ctx2 = 0;
+int output_weak2 = 0; /* should stay zero */
+
+/* same "subprog" name in all files, but it's ok because they all are static */
+static __noinline int subprog(int x)
+{
+ /* but different formula */
+ return x * 2;
+}
+
+/* Global functions can't be void */
+int set_output_val2(int x)
+{
+ output_val2 = 2 * x + 2 * subprog(x);
+ return 2 * x;
+}
+
+/* This function can't be verified as global, as it assumes raw_tp/sys_enter
+ * context and accesses syscall id (second argument). So we mark it as
+ * __hidden, so that libbpf will mark it as static in the final object file,
+ * right before verifying it in the kernel.
+ *
+ * But we don't mark it as __hidden here, rather at extern site. __hidden is
+ * "contaminating" visibility, so it will get propagated from either extern or
+ * actual definition (including from the losing __weak definition).
+ */
+void set_output_ctx2(__u64 *ctx)
+{
+ output_ctx2 = ctx[1]; /* long id, same as in BPF_PROG below */
+}
+
+/* this weak instance should lose, because it will be processed second */
+__weak int set_output_weak(int x)
+{
+ output_weak2 = x;
+ return 2 * x;
+}
+
+extern int set_output_val1(int x);
+
+/* here we'll force set_output_ctx1() to be __hidden in the final obj file */
+__hidden extern void set_output_ctx1(__u64 *ctx);
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler2, struct pt_regs *regs, long id)
+{
+ if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
+ return 0;
+
+ set_output_val1(2000);
+ set_output_ctx1(ctx); /* ctx definition is hidden in BPF_PROG macro */
+
+ /* keep input value the same across both files to avoid dependency on
+ * handler call order; differentiate by output_weak1 vs output_weak2.
+ */
+ set_output_weak(42);
+
+ return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
--
2.30.2
