On 4/23/21 10:55 AM, Andrii Nakryiko wrote:
On Fri, Apr 23, 2021 at 10:35 AM Yonghong Song <yhs@xxxxxx> wrote:
On 4/23/21 10:18 AM, Andrii Nakryiko wrote:
On Thu, Apr 22, 2021 at 5:50 PM Yonghong Song <yhs@xxxxxx> wrote:
On 4/16/21 1:24 PM, Andrii Nakryiko wrote:
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>
Ack with a small nit below.
Acked-by: Yonghong Song <yhs@xxxxxx>
---
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 666b462c1218..427ccfec1a6a 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -308,9 +308,10 @@ 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..03bf8ef131ce
--- /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;
Since the new compiler (llvm13) is recommended for this patch set.
We can simplify the above two definition with
int my_tid __weak;
long syscall_id __weak;
The same for the other file.
This is not about old vs new compilers. I wanted to use .rodata
variables, but I'll switch to .bss, no problem.
I see. You can actually hone one "const volatile ing my_tid __weak = 0"
and another "long syscall_id __weak". This way, you will be able to
test both .rodata and .bss section.
I wonder if you meant to have one my_tid __weak in .bss and another
my_tid __weak in .rodata. Or just my_tid in .bss and syscall_id in
.rodata?
If the former (mixing ELF sections across definitions of the same
symbol), then it's disallowed right now. libbpf will error out on
mismatched sections. I tested this with normal compilation, it does
work and the final section is the section of the winner.
But I think that's quite confusing, actually, so I'm going to leave it
disallowed for now. E.g., if one file expects a read-write variable
and another expects that same variable to be read-only, and the winner
ends up being read-only one, then the file expecting read-write will
essentially have incorrect code (and will be rejected by BPF verifier,
if anything attempts to write). So I think it's better to reject it at
the linking time.
But I'll do one (my_tid) as .bss, and another (syscall_id) as .rodata.
I mean this one. Permitting the same variable in both .bss and .rodata
sections is never a good practice.
But I am also okay with the current form
to *satisfy* llvm10 some people may still use.
+
+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);
+
[...]
