tools/bpf: selftests : Explain bpf_iter test failures with llvm 10.0.0 (99aaf53e) · Commits · 戴 / test

Commit ("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@kernel.org> Signed-off-by:

Yonghong Song <yhs@fb.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200513180215.2949237-1-yhs@fb.com

tools/testing/selftests/bpf/README.rst

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Original line number	Diff line number	Diff line
		==================
		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.

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