4 General instructions on running selftests can be found in
5 `Documentation/bpf/bpf_devel_QA.rst`__.
7 __ /Documentation/bpf/bpf_devel_QA.rst#q-how-to-run-bpf-selftests
13 BPF employs a continuous integration (CI) system to check patch submission in an
14 automated fashion. The system runs selftests for each patch in a series. Results
15 are propagated to patchwork, where failures are highlighted similar to
16 violations of other checks (such as additional warnings being emitted or a
17 ``scripts/checkpatch.pl`` reported deficiency):
19 https://patchwork.kernel.org/project/netdevbpf/list/?delegate=121173
21 The CI system executes tests on multiple architectures. It uses a kernel
22 configuration derived from both the generic and architecture specific config
23 file fragments below ``tools/testing/selftests/bpf/`` (e.g., ``config`` and
29 It is possible for some architectures to not have support for all BPF features.
30 In such a case tests in CI may fail. An example of such a shortcoming is BPF
31 trampoline support on IBM's s390x architecture. For cases like this, an in-tree
32 deny list file, located at ``tools/testing/selftests/bpf/DENYLIST.<arch>``, can
33 be used to prevent the test from running on such an architecture.
35 In addition to that, the generic ``tools/testing/selftests/bpf/DENYLIST`` is
36 honored on every architecture running tests.
38 These files are organized in three columns. The first column lists the test in
39 question. This can be the name of a test suite or of an individual test. The
40 remaining two columns provide additional meta data that helps identify and
41 classify the entry: column two is a copy and paste of the error being reported
42 when running the test in the setting in question. The third column, if
43 available, summarizes the underlying problem. A value of ``trampoline``, for
44 example, indicates that lack of trampoline support is causing the test to fail.
45 This last entry helps identify tests that can be re-enabled once such support is
48 =========================
49 Running Selftests in a VM
50 =========================
52 It's now possible to run the selftests using ``tools/testing/selftests/bpf/vmtest.sh``.
53 The script tries to ensure that the tests are run with the same environment as they
54 would be run post-submit in the CI used by the Maintainers, with the exception
55 that deny lists are not automatically honored.
57 This script uses the in-tree kernel configuration and downloads a VM userspace
58 image from the system used by the CI. It builds the kernel (without overwriting
59 your existing Kconfig), recompiles the bpf selftests, runs them (by default
60 ``tools/testing/selftests/bpf/test_progs``) and saves the resulting output (by
61 default in ``~/.bpf_selftests``).
64 - clang (preferably built from sources, https://github.com/llvm/llvm-project);
65 - pahole (preferably built from sources, https://git.kernel.org/pub/scm/devel/pahole/pahole.git/);
67 - docutils (for ``rst2man``);
70 For more information about using the script, run:
72 .. code-block:: console
74 $ tools/testing/selftests/bpf/vmtest.sh -h
76 In case of linker errors when running selftests, try using static linking:
78 .. code-block:: console
80 $ LDLIBS=-static PKG_CONFIG='pkg-config --static' vmtest.sh
82 .. note:: Some distros may not support static linking.
84 .. note:: The script uses pahole and clang based on host environment setting.
85 If you want to change pahole and llvm, you can change `PATH` environment
86 variable in the beginning of script.
88 .. note:: The script currently only supports x86_64 and s390x architectures.
90 Additional information about selftest failures are
93 profiler[23] test failures with clang/llvm <12.0.0
94 ==================================================
96 With clang/llvm <12.0.0, the profiler[23] test may fail.
97 The symptom looks like
101 // r9 is a pointer to map_value
103 17: bf 96 00 00 00 00 00 00 r6 = r9
104 18: 0f 76 00 00 00 00 00 00 r6 += r7
105 math between map_value pointer and register with unbounded min value is not allowed
107 // the instructions below will not be seen in the verifier log
108 19: a5 07 01 00 01 01 00 00 if r7 < 257 goto +1
109 20: bf 96 00 00 00 00 00 00 r6 = r9
112 The verifier will reject such code with above error.
113 At insn 18 the r7 is indeed unbounded. The later insn 19 checks the bounds and
114 the insn 20 undoes map_value addition. It is currently impossible for the
115 verifier to understand such speculative pointer arithmetic.
116 Hence `this patch`__ addresses it on the compiler side. It was committed on llvm 12.
118 __ https://github.com/llvm/llvm-project/commit/ddf1864ace484035e3cde5e83b3a31ac81e059c6
120 The corresponding C code
124 for (int i = 0; i < MAX_CGROUPS_PATH_DEPTH; i++) {
125 filepart_length = bpf_probe_read_str(payload, ...);
126 if (filepart_length <= MAX_PATH) {
127 barrier_var(filepart_length); // workaround
128 payload += filepart_length;
132 bpf_iter test failures with clang/llvm 10.0.0
133 =============================================
135 With clang/llvm 10.0.0, the following two bpf_iter tests failed:
136 * ``bpf_iter/ipv6_route``
137 * ``bpf_iter/netlink``
139 The symptom for ``bpf_iter/ipv6_route`` looks like
143 2: (79) r8 = *(u64 *)(r1 +8)
147 ; BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
148 16: (7b) *(u64 *)(r8 +64) = r2
149 only read is supported
151 The symptom for ``bpf_iter/netlink`` looks like
155 ; struct netlink_sock *nlk = ctx->sk;
156 2: (79) r7 = *(u64 *)(r1 +8)
160 ; BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
161 17: (7b) *(u64 *)(r7 +0) = r2
162 only read is supported
164 This is due to a llvm BPF backend bug. `The fix`__
165 has been pushed to llvm 10.x release branch and will be
166 available in 10.0.1. The patch is available in llvm 11.0.0 trunk.
168 __ https://github.com/llvm/llvm-project/commit/3cb7e7bf959dcd3b8080986c62e10a75c7af43f0
170 bpf_verif_scale/loop6.bpf.o test failure with Clang 12
171 ======================================================
173 With Clang 12, the following bpf_verif_scale test failed:
174 * ``bpf_verif_scale/loop6.bpf.o``
176 The verifier output looks like
180 R1 type=ctx expected=fp
181 The sequence of 8193 jumps is too complex.
183 The reason is compiler generating the following code
187 ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
188 14: 16 05 40 00 00 00 00 00 if w5 == 0 goto +64 <LBB0_6>
189 15: bc 51 00 00 00 00 00 00 w1 = w5
190 16: 04 01 00 00 ff ff ff ff w1 += -1
191 17: 67 05 00 00 20 00 00 00 r5 <<= 32
192 18: 77 05 00 00 20 00 00 00 r5 >>= 32
193 19: a6 01 01 00 05 00 00 00 if w1 < 5 goto +1 <LBB0_4>
194 20: b7 05 00 00 06 00 00 00 r5 = 6
195 00000000000000a8 <LBB0_4>:
196 21: b7 02 00 00 00 00 00 00 r2 = 0
197 22: b7 01 00 00 00 00 00 00 r1 = 0
198 ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
199 23: 7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
200 24: 7b 5a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r5
202 Note that insn #15 has w1 = w5 and w1 is refined later but
203 r5(w5) is eventually saved on stack at insn #24 for later use.
204 This cause later verifier failure. The bug has been `fixed`__ in
207 __ https://github.com/llvm/llvm-project/commit/1959ead525b8830cc8a345f45e1c3ef9902d3229
209 BPF CO-RE-based tests and Clang version
210 =======================================
212 A set of selftests use BPF target-specific built-ins, which might require
213 bleeding-edge Clang versions (Clang 12 nightly at this time).
215 Few sub-tests of core_reloc test suit (part of test_progs test runner) require
216 the following built-ins, listed with corresponding Clang diffs introducing
217 them to Clang/LLVM. These sub-tests are going to be skipped if Clang is too
218 old to support them, they shouldn't cause build failures or runtime test
221 - __builtin_btf_type_id() [0_, 1_, 2_];
222 - __builtin_preserve_type_info(), __builtin_preserve_enum_value() [3_, 4_].
224 .. _0: https://github.com/llvm/llvm-project/commit/6b01b465388b204d543da3cf49efd6080db094a9
225 .. _1: https://github.com/llvm/llvm-project/commit/072cde03aaa13a2c57acf62d79876bf79aa1919f
226 .. _2: https://github.com/llvm/llvm-project/commit/00602ee7ef0bf6c68d690a2bd729c12b95c95c99
227 .. _3: https://github.com/llvm/llvm-project/commit/6d218b4adb093ff2e9764febbbc89f429412006c
228 .. _4: https://github.com/llvm/llvm-project/commit/6d6750696400e7ce988d66a1a00e1d0cb32815f8
230 Floating-point tests and Clang version
231 ======================================
233 Certain selftests, e.g. core_reloc, require support for the floating-point
234 types, which was introduced in `Clang 13`__. The older Clang versions will
235 either crash when compiling these tests, or generate an incorrect BTF.
237 __ https://github.com/llvm/llvm-project/commit/a7137b238a07d9399d3ae96c0b461571bd5aa8b2
239 Kernel function call test and Clang version
240 ===========================================
242 Some selftests (e.g. kfunc_call and bpf_tcp_ca) require a LLVM support
243 to generate extern function in BTF. It was introduced in `Clang 13`__.
245 Without it, the error from compiling bpf selftests looks like:
247 .. code-block:: console
249 libbpf: failed to find BTF for extern 'tcp_slow_start' [25] section: -2
251 __ https://github.com/llvm/llvm-project/commit/886f9ff53155075bd5f1e994f17b85d1e1b7470c
253 btf_tag test and Clang version
254 ==============================
256 The btf_tag selftest requires LLVM support to recognize the btf_decl_tag and
257 btf_type_tag attributes. They are introduced in `Clang 14` [0_, 1_].
258 The subtests ``btf_type_tag_user_{mod1, mod2, vmlinux}`` also requires
259 pahole version ``1.23``.
261 Without them, the btf_tag selftest will be skipped and you will observe:
263 .. code-block:: console
265 #<test_num> btf_tag:SKIP
267 .. _0: https://github.com/llvm/llvm-project/commit/a162b67c98066218d0d00aa13b99afb95d9bb5e6
268 .. _1: https://github.com/llvm/llvm-project/commit/3466e00716e12e32fdb100e3fcfca5c2b3e8d784
270 Clang dependencies for static linking tests
271 ===========================================
273 linked_vars, linked_maps, and linked_funcs tests depend on `Clang fix`__ to
274 generate valid BTF information for weak variables. Please make sure you use
275 Clang that contains the fix.
277 __ https://github.com/llvm/llvm-project/commit/968292cb93198442138128d850fd54dc7edc0035
279 Clang relocation changes
280 ========================
282 Clang 13 patch `clang reloc patch`_ made some changes on relocations such
283 that existing relocation types are broken into more types and
284 each new type corresponds to only one way to resolve relocation.
285 See `kernel llvm reloc`_ for more explanation and some examples.
286 Using clang 13 to compile old libbpf which has static linker support,
287 there will be a compilation failure::
289 libbpf: ELF relo #0 in section #6 has unexpected type 2 in .../bpf_tcp_nogpl.bpf.o
291 Here, ``type 2`` refers to new relocation type ``R_BPF_64_ABS64``.
292 To fix this issue, user newer libbpf.
295 .. _clang reloc patch: https://github.com/llvm/llvm-project/commit/6a2ea84600ba4bd3b2733bd8f08f5115eb32164b
296 .. _kernel llvm reloc: /Documentation/bpf/llvm_reloc.rst
298 Clang dependencies for the u32 spill test (xdpwall)
299 ===================================================
300 The xdpwall selftest requires a change in `Clang 14`__.
302 Without it, the xdpwall selftest will fail and the error message
303 from running test_progs will look like:
305 .. code-block:: console
307 test_xdpwall:FAIL:Does LLVM have https://github.com/llvm/llvm-project/commit/ea72b0319d7b0f0c2fcf41d121afa5d031b319d5? unexpected error: -4007
309 __ https://github.com/llvm/llvm-project/commit/ea72b0319d7b0f0c2fcf41d121afa5d031b319d5