Commit 6879c042e105 ("tools/bpf: selftests: Add bpf_iter selftests")
added self tests for bpf_iter feature. But two subtests
ipv6_route and netlink needs llvm latest 10.x release branch
or trunk due to a bug in llvm BPF backend. This patch added
the file README.rst to document these two failures
so people using llvm 10.0.0 can be aware of them.
Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
tools/testing/selftests/bpf/README.rst | 43 ++++++++++++++++++++++++++
1 file changed, 43 insertions(+)
create mode 100644 tools/testing/selftests/bpf/README.rst
diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
new file mode 100644
index 000000000000..0f67f1b470b0
--- /dev/null
+++ b/tools/testing/selftests/bpf/README.rst
@@ -0,0 +1,43 @@
+==================
+BPF Selftest Notes
+==================
+
+Additional information about selftest failures are
+documented here.
+
+bpf_iter test failures with clang/llvm 10.0.0
+=============================================
+
+With clang/llvm 10.0.0, the following two bpf_iter tests failed:
+ * ``bpf_iter/ipv6_route``
+ * ``bpf_iter/netlink``
+
+The symptom for ``bpf_iter/ipv6_route`` looks like
+
+.. code-block:: c
+
+ 2: (79) r8 = *(u64 *)(r1 +8)
+ ...
+ 14: (bf) r2 = r8
+ 15: (0f) r2 += r1
+ ; BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
+ 16: (7b) *(u64 *)(r8 +64) = r2
+ only read is supported
+
+The symptom for ``bpf_iter/netlink`` looks like
+
+.. code-block:: c
+
+ ; struct netlink_sock *nlk = ctx->sk;
+ 2: (79) r7 = *(u64 *)(r1 +8)
+ ...
+ 15: (bf) r2 = r7
+ 16: (0f) r2 += r1
+ ; BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
+ 17: (7b) *(u64 *)(r7 +0) = r2
+ only read is supported
+
+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.
--
2.24.1
