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Diffstat (limited to 'tools/testing/selftests/bpf/README.rst')
| -rw-r--r-- | tools/testing/selftests/bpf/README.rst | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst index e885d351595f..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 ============================================= @@ -43,3 +81,24 @@ This is due to a llvm BPF backend bug. The fix https://reviews.llvm.org/D78466 has been pushed to llvm 10.x release branch and will be available in 10.0.1. The fix is available in llvm 11.0.0 trunk. + +BPF CO-RE-based tests and Clang version +======================================= + +A set of selftests use BPF target-specific built-ins, which might require +bleeding-edge Clang versions (Clang 12 nightly at this time). + +Few sub-tests of core_reloc test suit (part of test_progs test runner) require +the following built-ins, listed with corresponding Clang diffs introducing +them to Clang/LLVM. These sub-tests are going to be skipped if Clang is too +old to support them, they shouldn't cause build failures or runtime test +failures: + + - __builtin_btf_type_id() ([0], [1], [2]); + - __builtin_preserve_type_info(), __builtin_preserve_enum_value() ([3], [4]). + + [0] https://reviews.llvm.org/D74572 + [1] https://reviews.llvm.org/D74668 + [2] https://reviews.llvm.org/D85174 + [3] https://reviews.llvm.org/D83878 + [4] https://reviews.llvm.org/D83242 |