OSCL-LXR linux-6.0.1/​tools/​testing/​selftests/​bpf/​README.rst	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 ==================
 BPF Selftest Notes
 ==================
 General instructions on running selftests can be found in
 `Documentation/bpf/bpf_devel_QA.rst`__.
 
 __ /Documentation/bpf/bpf_devel_QA.rst#q-how-to-run-bpf-selftests
 
 =========================
 Running Selftests in a VM
 =========================
 
 It's now possible to run the selftests using ``tools/testing/selftests/bpf/vmtest.sh``.
 The script tries to ensure that the tests are run with the same environment as they
 would be run post-submit in the CI used by the Maintainers.
 
 This script downloads a suitable Kconfig and VM userspace image from the system used by
 the CI. It builds the kernel (without overwriting your existing Kconfig), recompiles the
 bpf selftests, runs them (by default ``tools/testing/selftests/bpf/test_progs``) and
 saves the resulting output (by default in ``~/.bpf_selftests``).
 
 Script dependencies:
 - clang (preferably built from sources, https://github.com/llvm/llvm-project);
 - pahole (preferably built from sources, https://git.kernel.org/pub/scm/devel/pahole/pahole.git/);
 - qemu;
 - docutils (for ``rst2man``);
 - libcap-devel.
 
 For more information on about using the script, run:
 
 .. code-block:: console
 
   $ tools/testing/selftests/bpf/vmtest.sh -h
 
 In case of linker errors when running selftests, try using static linking:
 
 .. code-block:: console
 
   $ LDLIBS=-static vmtest.sh
 
 .. note:: Some distros may not support static linking.
 
 .. note:: The script uses pahole and clang based on host environment setting.
           If you want to change pahole and llvm, you can change `PATH` environment
           variable in the beginning of script.
 
 .. note:: The script currently only supports x86_64 and s390x architectures.
 
 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 `this patch`__ addresses it on the compiler side. It was committed on llvm 12.
 
 __ https://reviews.llvm.org/D85570
 
 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
 =============================================
 
 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`__
 has been pushed to llvm 10.x release branch and will be
 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
 =======================================
 
 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
 
 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
 
 btf_tag test and Clang version
 ==============================
 
 The btf_tag selftest requires LLVM support to recognize the btf_decl_tag and
 btf_type_tag attributes. They are introduced in `Clang 14` [0_, 1_].
 The subtests ``btf_type_tag_user_{mod1, mod2, vmlinux}`` also requires
 pahole version ``1.23``.
 
 Without them, the btf_tag selftest will be skipped and you will observe:
 
 .. code-block:: console
 
   #<test_num> btf_tag:SKIP
 
 .. _0: https://reviews.llvm.org/D111588
 .. _1: https://reviews.llvm.org/D111199
 
 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
 
 Clang relocation changes
 ========================
 
 Clang 13 patch `clang reloc patch`_  made some changes on relocations such
 that existing relocation types are broken into more types and
 each new type corresponds to only one way to resolve relocation.
 See `kernel llvm reloc`_ for more explanation and some examples.
 Using clang 13 to compile old libbpf which has static linker support,
 there will be a compilation failure::
 
   libbpf: ELF relo #0 in section #6 has unexpected type 2 in .../bpf_tcp_nogpl.o
 
 Here, ``type 2`` refers to new relocation type ``R_BPF_64_ABS64``.
 To fix this issue, user newer libbpf.
 
 .. Links
 .. _clang reloc patch: https://reviews.llvm.org/D102712
 .. _kernel llvm reloc: /Documentation/bpf/llvm_reloc.rst
 
 Clang dependencies for the u32 spill test (xdpwall)
 ===================================================
 The xdpwall selftest requires a change in `Clang 14`__.
 
 Without it, the xdpwall selftest will fail and the error message
 from running test_progs will look like:
 
 .. code-block:: console
 
   test_xdpwall:FAIL:Does LLVM have https://reviews.llvm.org/D109073? unexpected error: -4007
 
 __ https://reviews.llvm.org/D109073

This page was automatically generated by the 2.1.0 LXR engine. The LXR team