selftests/bpf: Add tests for symbol versioning for uprobe

This exercises the newly added dynsym symbol versioning logics.
Now we accept symbols in form of func, func@LIB_VERSION or
func@@LIB_VERSION.

The test rely on liburandom_read.so. For liburandom_read.so, we have:

$ nm -D liburandom_read.so
w __cxa_finalize@GLIBC_2.17
w __gmon_start__
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
0000000000000000 A LIBURANDOM_READ_1.0.0
0000000000000000 A LIBURANDOM_READ_2.0.0
000000000000081c T urandlib_api@@LIBURANDOM_READ_2.0.0
0000000000000814 T urandlib_api@LIBURANDOM_READ_1.0.0
0000000000000824 T urandlib_api_sameoffset@LIBURANDOM_READ_1.0.0
0000000000000824 T urandlib_api_sameoffset@@LIBURANDOM_READ_2.0.0
000000000000082c T urandlib_read_without_sema@@LIBURANDOM_READ_1.0.0
00000000000007c4 T urandlib_read_with_sema@@LIBURANDOM_READ_1.0.0
0000000000011018 D urandlib_read_with_sema_semaphore@@LIBURANDOM_READ_1.0.0

For `urandlib_api`, specifying `urandlib_api` will cause a conflict because
there are two symbols named urandlib_api and both are global bind.
For `urandlib_api_sameoffset`, there are also two symbols in the .so, but
both are at the same offset and essentially they refer to the same function
so no conflict.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230918024813.237475-4-hengqi.chen@gmail.com

selftests/bpf: Add urandom_read shared lib and USDTs

Extend urandom_read helper binary to include USDTs of 4 combinations:
semaphore/semaphoreless (refcounted and non-refcounted) and based in
executable or shared library. We also extend urandom_read with ability
to report it's own PID to parent process and wait for parent process to
ready itself up for tracing urandom_read. We utilize popen() and
underlying pipe properties for proper signaling.

Once urandom_read is ready, we add few tests to validate that libbpf's
USDT attachment handles all the above combinations of semaphore (or lack
of it) and static or shared library USDTs. Also, we validate that libbpf
handles shared libraries both with PID filter and without one (i.e., -1
for PID argument).

Having the shared library case tested with and without PID is important
because internal logic differs on kernels that don't support BPF
cookies. On such older kernels, attaching to USDTs in shared libraries
without specifying concrete PID doesn't work in principle, because it's
impossible to determine shared library's load address to derive absolute
IPs for uprobe attachments. Without absolute IPs, it's impossible to
perform correct look up of USDT spec based on uprobe's absolute IP (the
only kind available from BPF at runtime). This is not the problem on
newer kernels with BPF cookie as we don't need IP-to-ID lookup because
BPF cookie value *is* spec ID.

So having those two situations as separate subtests is good because
libbpf CI is able to test latest selftests against old kernels (e.g.,
4.9 and 5.5), so we'll be able to disable PID-less shared lib attachment
for old kernels, but will still leave PID-specific one enabled to validate
this legacy logic is working correctly.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20220404234202.331384-8-andrii@kernel.org