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Diffstat (limited to 'tools/testing/selftests/bpf/README.rst')
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diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst index 66acfcf15ff2..ac9eda830187 100644 --- a/tools/testing/selftests/bpf/README.rst +++ b/tools/testing/selftests/bpf/README.rst @@ -7,6 +7,44 @@ General instructions on running selftests can be found in Additional information about selftest failures are documented here. +profiler[23] test failures with clang/llvm <12.0.0 +================================================== + +With clang/llvm <12.0.0, the profiler[23] test may fail. +The symptom looks like + +.. code-block:: c + + // r9 is a pointer to map_value + // r7 is a scalar + 17: bf 96 00 00 00 00 00 00 r6 = r9 + 18: 0f 76 00 00 00 00 00 00 r6 += r7 + math between map_value pointer and register with unbounded min value is not allowed + + // the instructions below will not be seen in the verifier log + 19: a5 07 01 00 01 01 00 00 if r7 < 257 goto +1 + 20: bf 96 00 00 00 00 00 00 r6 = r9 + // r6 is used here + +The verifier will reject such code with above error. +At insn 18 the r7 is indeed unbounded. The later insn 19 checks the bounds and +the insn 20 undoes map_value addition. It is currently impossible for the +verifier to understand such speculative pointer arithmetic. +Hence + https://reviews.llvm.org/D85570 +addresses it on the compiler side. It was committed on llvm 12. + +The corresponding C code +.. code-block:: c + + for (int i = 0; i < MAX_CGROUPS_PATH_DEPTH; i++) { + filepart_length = bpf_probe_read_str(payload, ...); + if (filepart_length <= MAX_PATH) { + barrier_var(filepart_length); // workaround + payload += filepart_length; + } + } + bpf_iter test failures with clang/llvm 10.0.0 ============================================= |