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-rw-r--r--tools/testing/selftests/bpf/README.rst71
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diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
index fd148b8410fa..3353778c30f8 100644
--- a/tools/testing/selftests/bpf/README.rst
+++ b/tools/testing/selftests/bpf/README.rst
@@ -111,6 +111,45 @@ available in 10.0.1. The patch is available in llvm 11.0.0 trunk.
__ https://reviews.llvm.org/D78466
+bpf_verif_scale/loop6.o test failure with Clang 12
+==================================================
+
+With Clang 12, the following bpf_verif_scale test failed:
+ * ``bpf_verif_scale/loop6.o``
+
+The verifier output looks like
+
+.. code-block:: c
+
+ R1 type=ctx expected=fp
+ The sequence of 8193 jumps is too complex.
+
+The reason is compiler generating the following code
+
+.. code-block:: c
+
+ ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
+ 14: 16 05 40 00 00 00 00 00 if w5 == 0 goto +64 <LBB0_6>
+ 15: bc 51 00 00 00 00 00 00 w1 = w5
+ 16: 04 01 00 00 ff ff ff ff w1 += -1
+ 17: 67 05 00 00 20 00 00 00 r5 <<= 32
+ 18: 77 05 00 00 20 00 00 00 r5 >>= 32
+ 19: a6 01 01 00 05 00 00 00 if w1 < 5 goto +1 <LBB0_4>
+ 20: b7 05 00 00 06 00 00 00 r5 = 6
+ 00000000000000a8 <LBB0_4>:
+ 21: b7 02 00 00 00 00 00 00 r2 = 0
+ 22: b7 01 00 00 00 00 00 00 r1 = 0
+ ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
+ 23: 7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
+ 24: 7b 5a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r5
+
+Note that insn #15 has w1 = w5 and w1 is refined later but
+r5(w5) is eventually saved on stack at insn #24 for later use.
+This cause later verifier failure. The bug has been `fixed`__ in
+Clang 13.
+
+__ https://reviews.llvm.org/D97479
+
BPF CO-RE-based tests and Clang version
=======================================
@@ -131,3 +170,35 @@ failures:
.. _2: https://reviews.llvm.org/D85174
.. _3: https://reviews.llvm.org/D83878
.. _4: https://reviews.llvm.org/D83242
+
+Floating-point tests and Clang version
+======================================
+
+Certain selftests, e.g. core_reloc, require support for the floating-point
+types, which was introduced in `Clang 13`__. The older Clang versions will
+either crash when compiling these tests, or generate an incorrect BTF.
+
+__ https://reviews.llvm.org/D83289
+
+Kernel function call test and Clang version
+===========================================
+
+Some selftests (e.g. kfunc_call and bpf_tcp_ca) require a LLVM support
+to generate extern function in BTF. It was introduced in `Clang 13`__.
+
+Without it, the error from compiling bpf selftests looks like:
+
+.. code-block:: console
+
+ libbpf: failed to find BTF for extern 'tcp_slow_start' [25] section: -2
+
+__ https://reviews.llvm.org/D93563
+
+Clang dependencies for static linking tests
+===========================================
+
+linked_vars, linked_maps, and linked_funcs tests depend on `Clang fix`__ to
+generate valid BTF information for weak variables. Please make sure you use
+Clang that contains the fix.
+
+__ https://reviews.llvm.org/D100362