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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
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After some experiences I found that urandom_read does not need to be
linked statically. When the 'read' syscall call is moved to separate
non-inlined function then bpf_get_stackid() is able to find
the executable in stack trace and extract its build_id from it.
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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This new test captures stackmap with build_id with hardware event
PERF_COUNT_HW_CPU_CYCLES.
Because we only support one ips-to-build_id lookup per cpu in NMI
context, stack_amap will not be able to do the lookup in this test.
Therefore, we didn't do compare_stack_ips(), as it will alwasy fail.
urandom_read.c is extended to run configurable cycles so that it can be
caught by the perf event.
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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test_stacktrace_build_id() is added. It accesses tracepoint urandom_read
with "dd" and "urandom_read" and gathers stack traces. Then it reads the
stack traces from the stackmap.
urandom_read is a statically link binary that reads from /dev/urandom.
test_stacktrace_build_id() calls readelf to read build ID of urandom_read
and compares it with build ID from the stackmap.
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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