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llvm patch https://reviews.llvm.org/D84002 permitted to emit empty rodata datasec if the elf .rodata section contains read-only data from local variables. These local variables will be not emitted as BTF_KIND_VARs since llvm converted these local variables as static variables with private linkage without debuginfo types. Such an empty rodata datasec will make skeleton code generation easy since for skeleton a rodata struct will be generated if there is a .rodata elf section. The existence of a rodata btf datasec is also consistent with the existence of a rodata map created by libbpf. The btf with such an empty rodata datasec will fail in the kernel though as kernel will reject a datasec with zero vlen and zero size. For example, for the below code, int sys_enter(void *ctx) { int fmt[6] = {1, 2, 3, 4, 5, 6}; int dst[6]; bpf_probe_read(dst, sizeof(dst), fmt); return 0; } We got the below btf (bpftool btf dump ./test.o): [1] PTR '(anon)' type_id=0 [2] FUNC_PROTO '(anon)' ret_type_id=3 vlen=1 'ctx' type_id=1 [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [4] FUNC 'sys_enter' type_id=2 linkage=global [5] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [6] ARRAY '(anon)' type_id=5 index_type_id=7 nr_elems=4 [7] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none) [8] VAR '_license' type_id=6, linkage=global-alloc [9] DATASEC '.rodata' size=0 vlen=0 [10] DATASEC 'license' size=0 vlen=1 type_id=8 offset=0 size=4 When loading the ./test.o to the kernel with bpftool, we see the following error: libbpf: Error loading BTF: Invalid argument(22) libbpf: magic: 0xeb9f ... [6] ARRAY (anon) type_id=5 index_type_id=7 nr_elems=4 [7] INT __ARRAY_SIZE_TYPE__ size=4 bits_offset=0 nr_bits=32 encoding=(none) [8] VAR _license type_id=6 linkage=1 [9] DATASEC .rodata size=24 vlen=0 vlen == 0 libbpf: Error loading .BTF into kernel: -22. BTF is optional, ignoring. Basically, libbpf changed .rodata datasec size to 24 since elf .rodata section size is 24. The kernel then rejected the BTF since vlen = 0. Note that the above kernel verifier failure can be worked around with changing local variable "fmt" to a static or global, optionally const, variable. This patch permits a datasec with vlen = 0 in kernel. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20210119153519.3901963-1-yhs@fb.com |
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benchs | ||
bpf_testmod | ||
gnu | ||
map_tests | ||
prog_tests | ||
progs | ||
verifier | ||
.gitignore | ||
bench.c | ||
bench.h | ||
bpf_legacy.h | ||
bpf_rand.h | ||
bpf_rlimit.h | ||
bpf_tcp_helpers.h | ||
bpf_util.h | ||
btf_helpers.c | ||
btf_helpers.h | ||
cgroup_helpers.c | ||
cgroup_helpers.h | ||
config | ||
flow_dissector_load.c | ||
flow_dissector_load.h | ||
get_cgroup_id_user.c | ||
ima_setup.sh | ||
Makefile | ||
netcnt_common.h | ||
network_helpers.c | ||
network_helpers.h | ||
README.rst | ||
settings | ||
test_bpftool.py | ||
test_bpftool.sh | ||
test_bpftool_build.sh | ||
test_bpftool_metadata.sh | ||
test_btf.h | ||
test_cgroup_storage.c | ||
test_cpp.cpp | ||
test_dev_cgroup.c | ||
test_flow_dissector.c | ||
test_flow_dissector.sh | ||
test_ftrace.sh | ||
test_iptunnel_common.h | ||
test_kmod.sh | ||
test_lirc_mode2.sh | ||
test_lirc_mode2_user.c | ||
test_lpm_map.c | ||
test_lru_map.c | ||
test_lwt_ip_encap.sh | ||
test_lwt_seg6local.sh | ||
test_maps.c | ||
test_maps.h | ||
test_netcnt.c | ||
test_offload.py | ||
test_progs.c | ||
test_progs.h | ||
test_select_reuseport_common.h | ||
test_skb_cgroup_id.sh | ||
test_skb_cgroup_id_user.c | ||
test_sock.c | ||
test_sock_addr.c | ||
test_sock_addr.sh | ||
test_socket_cookie.c | ||
test_sockmap.c | ||
test_stub.c | ||
test_sysctl.c | ||
test_tag.c | ||
test_tc_edt.sh | ||
test_tc_redirect.sh | ||
test_tc_tunnel.sh | ||
test_tcp_check_syncookie.sh | ||
test_tcp_check_syncookie_user.c | ||
test_tcp_hdr_options.h | ||
test_tcpbpf.h | ||
test_tcpnotify.h | ||
test_tcpnotify_user.c | ||
test_tunnel.sh | ||
test_verifier.c | ||
test_verifier_log.c | ||
test_xdp_meta.sh | ||
test_xdp_redirect.sh | ||
test_xdp_veth.sh | ||
test_xdp_vlan.sh | ||
test_xdp_vlan_mode_generic.sh | ||
test_xdp_vlan_mode_native.sh | ||
test_xdping.sh | ||
test_xsk.sh | ||
testing_helpers.c | ||
testing_helpers.h | ||
trace_helpers.c | ||
trace_helpers.h | ||
urandom_read.c | ||
with_addr.sh | ||
with_tunnels.sh | ||
xdping.c | ||
xdping.h | ||
xdpxceiver.c | ||
xdpxceiver.h | ||
xsk_prereqs.sh |
================== 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 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 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