Merge branch 'libbpf: Support symbol versioning for uprobe'

Hengqi Chen says:

====================
Dynamic symbols in shared library may have the same name, for example:

    $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
    000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
    000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
    000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5

    $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
      706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
      2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
      2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5

There are two pthread_rwlock_wrlock symbols in libc.so .dynsym section.
The one with @@ is the default version, the other is hidden.
Note that the version info is stored in .gnu.version and .gnu.version_d
sections of libc and the two symbols are at the _same_ offset.

Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
version suffix and both are global bind.

We could solve this by introducing symbol versioning ([0]). So that users can
specify func, func@LIB_VERSION or func@@LIB_VERSION to attach a uprobe.

This patchset resolves symbol conflicts and add symbol versioning for uprobe.
  - Patch 1 resolves symbol conflicts at the same offset
  - Patch 2 adds symbol versioning for dynsym
  - Patch 3 adds selftests for the above changes

Changes from v3:
  - Address comments from Andrii

Changes from v2:
  - Add uretprobe selfttest (Alan)
  - Check symbol exact match (Alan)
  - Fix typo (Jiri)

Changes from v1:
  - Address comments from Alan and Jiri
  - Add selftests (Someone reminds me that there is an attempt at [1]
    and part of the selftest code from Andrii is taken from there)

  [0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html
  [1]: https://lore.kernel.org/lkml/CAEf4BzZTrjjyyOm3ak9JsssPSh6T_ZmGd677a2rt5e5rBLUrpQ@mail.gmail.com/
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

1 files changed, 95 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe.c b/tools/testing/selftests/bpf/prog_tests/uprobe.c
new file mode 100644
index 000000000000..cf3e0e7a64fa
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Hengqi Chen */
+
+#include <test_progs.h>
+#include "test_uprobe.skel.h"
+
+static FILE *urand_spawn(int *pid)
+{
+	FILE *f;
+
+	/* urandom_read's stdout is wired into f */
+	f = popen("./urandom_read 1 report-pid", "r");
+	if (!f)
+		return NULL;
+
+	if (fscanf(f, "%d", pid) != 1) {
+		pclose(f);
+		errno = EINVAL;
+		return NULL;
+	}
+
+	return f;
+}
+
+static int urand_trigger(FILE **urand_pipe)
+{
+	int exit_code;
+
+	/* pclose() waits for child process to exit and returns their exit code */
+	exit_code = pclose(*urand_pipe);
+	*urand_pipe = NULL;
+
+	return exit_code;
+}
+
+void test_uprobe(void)
+{
+	LIBBPF_OPTS(bpf_uprobe_opts, uprobe_opts);
+	struct test_uprobe *skel;
+	FILE *urand_pipe = NULL;
+	int urand_pid = 0, err;
+
+	skel = test_uprobe__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	urand_pipe = urand_spawn(&urand_pid);
+	if (!ASSERT_OK_PTR(urand_pipe, "urand_spawn"))
+		goto cleanup;
+
+	skel->bss->my_pid = urand_pid;
+
+	/* Manual attach uprobe to urandlib_api
+	 * There are two `urandlib_api` symbols in .dynsym section:
+	 *   - urandlib_api@LIBURANDOM_READ_1.0.0
+	 *   - urandlib_api@@LIBURANDOM_READ_2.0.0
+	 * Both are global bind and would cause a conflict if user
+	 * specify the symbol name without a version suffix
+	 */
+	uprobe_opts.func_name = "urandlib_api";
+	skel->links.test4 = bpf_program__attach_uprobe_opts(skel->progs.test4,
+							    urand_pid,
+							    "./liburandom_read.so",
+							    0 /* offset */,
+							    &uprobe_opts);
+	if (!ASSERT_ERR_PTR(skel->links.test4, "urandlib_api_attach_conflict"))
+		goto cleanup;
+
+	uprobe_opts.func_name = "urandlib_api@LIBURANDOM_READ_1.0.0";
+	skel->links.test4 = bpf_program__attach_uprobe_opts(skel->progs.test4,
+							    urand_pid,
+							    "./liburandom_read.so",
+							    0 /* offset */,
+							    &uprobe_opts);
+	if (!ASSERT_OK_PTR(skel->links.test4, "urandlib_api_attach_ok"))
+		goto cleanup;
+
+	/* Auto attach 3 u[ret]probes to urandlib_api_sameoffset */
+	err = test_uprobe__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	/* trigger urandom_read */
+	ASSERT_OK(urand_trigger(&urand_pipe), "urand_exit_code");
+
+	ASSERT_EQ(skel->bss->test1_result, 1, "urandlib_api_sameoffset");
+	ASSERT_EQ(skel->bss->test2_result, 1, "urandlib_api_sameoffset@v1");
+	ASSERT_EQ(skel->bss->test3_result, 3, "urandlib_api_sameoffset@@v2");
+	ASSERT_EQ(skel->bss->test4_result, 1, "urandlib_api");
+
+cleanup:
+	if (urand_pipe)
+		pclose(urand_pipe);
+	test_uprobe__destroy(skel);
+}