Re: [PATCH v5 bpf-next 3/4] selftest/bpf: Implement sample UNIX domain socket iterator program.
flat view
From: Yonghong Song <hidden>
Date: 2021-08-15 18:11:29
Also in:
bpf
On 8/13/21 5:21 PM, Kuniyuki Iwashima wrote:
From: Andrii Nakryiko <redacted> Date: Fri, 13 Aug 2021 16:25:53 -0700quoted
On Thu, Aug 12, 2021 at 9:46 AM Kuniyuki Iwashima [off-list ref] wrote:quoted
The iterator can output almost the same result compared to /proc/net/unix. The header line is aligned, and the Inode column uses "%8lu" because "%5lu" can be easily overflown. # cat /sys/fs/bpf/unix Num RefCount Protocol Flags Type St Inode PathIt's totally my OCD, but why the column name is not aligned with values? I mean the "Inode" column. It's left aligned, but values (numbers) are right-aligned? I'd fix that while applying, but I can't apply due to selftests failures, so please take a look.Ah, honestly, I've felt something strange about the column... will fix it!quoted
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ffff963c06689800: 00000002 00000000 00010000 0001 01 18697 private/defer ffff963c7c979c00: 00000002 00000000 00000000 0001 01 598245 @Hello@World@ # cat /proc/net/unix Num RefCount Protocol Flags Type St Inode Path ffff963c06689800: 00000002 00000000 00010000 0001 01 18697 private/defer ffff963c7c979c00: 00000002 00000000 00000000 0001 01 598245 @Hello@World@ Note that this prog requires the patch ([0]) for LLVM code gen. Thanks to Yonghong Song for analysing and fixing. [0] https://reviews.llvm.org/D107483 Signed-off-by: Kuniyuki Iwashima <redacted> Acked-by: Yonghong Song <redacted> ---This selftests breaks test_progs-no_alu32 ([0], the error log is super long and can freeze browser; it looks like an infinite loop and BPF verifier just keeps reporting it until it runs out of 1mln instructions or something). Please check what's going on there, I can't land it as it is right now. [0] https://github.com/kernel-patches/bpf/runs/3326071112?check_suite_focus=true#step:6:124288quoted
tools/testing/selftests/bpf/README.rst | 38 +++++++++ .../selftests/bpf/prog_tests/bpf_iter.c | 16 ++++ tools/testing/selftests/bpf/progs/bpf_iter.h | 8 ++ .../selftests/bpf/progs/bpf_iter_unix.c | 77 +++++++++++++++++++ .../selftests/bpf/progs/bpf_tracing_net.h | 4 + 5 files changed, 143 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_unix.c[...]quoted
+ /* The name of the abstract UNIX domain socket starts + * with '\0' and can contain '\0'. The null bytes + * should be escaped as done in unix_seq_show(). + */ + int i, len; +no_alu32 variant probably isn't happy about using int for this, it probably does << 32, >> 32 dance and loses track of actual value in the loop. You can try using u64 instead.Sorry, I missed the no_alu32 test. Changing int to __u64 fixed the error, thanks!
Indeed for no_alu32, the index has << 32 and >> 32, which makes
verifier *equivalent* register tracking not effective, see below:
96: r1 = r8
97: r1 <<= 32
98: r2 = r1
99: r2 >>= 32
100: if r2 > 109 goto +19 <LBB0_21>
101: r1 s>>= 32
102: if r1 s< 2 goto +17 <LBB0_21>
103: r9 = 1
104: r8 <<= 32
105: r8 >>= 32
Because these shifting, r1/r2/r8 equivalence cannot be
easily established, so verifier ends with conservative
r8 and cannot verify program successfully.
Using __u64 for 'i' and 'len', the upper bound is directly
tested:
98: if r8 > 109 goto +16 <LBB0_21>
99: if r8 < 2 goto +15 <LBB0_21>
and verifier is very happy with this.
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+ len = unix_sk->addr->len - sizeof(short); + + BPF_SEQ_PRINTF(seq, " @"); + + /* unix_mkname() tests this upper bound. */ + if (len < sizeof(struct sockaddr_un)) + for (i = 1; i < len; i++)if you move above if inside the loop to break out of the loop, does it change how Clang generates code? for (i = 1; i < len i++) { if (i >= sizeof(struct sockaddr_un)) break; BPF_SEQ_PRINTF(...); }Yes, but there seems little defference. Which is preferable? ---8<--- before (for inside if) <- -> after (if inside loop) 96: 07 08 00 00 fe ff ff ff r8 += -2 | ; for (i = 1; i < len; i++) { ; if (len < sizeof(struct sockaddr_un)) | 97: bf 81 00 00 00 00 00 00 r1 = r8 97: 25 08 10 00 6d 00 00 00 if r8 > 109 goto +16 <LBB0_21> | 98: 07 01 00 00 fc ff ff ff r1 += -4 ; for (i = 1; i < len; i++) | 99: 25 01 12 00 6b 00 00 00 if r1 > 107 goto +18 <LBB0_21> 98: a5 08 0f 00 02 00 00 00 if r8 < 2 goto +15 <LBB0_21> | 100: 07 08 00 00 fe ff ff ff r8 += -2 99: b7 09 00 00 01 00 00 00 r9 = 1 | 101: b7 09 00 00 01 00 00 00 r9 = 1 100: 05 00 16 00 00 00 00 00 goto +22 <LBB0_18> | 102: b7 06 00 00 02 00 00 00 r6 = 2 | 103: 05 00 17 00 00 00 00 00 goto +23 <LBB0_17> ... 111: 85 00 00 00 7e 00 00 00 call 126 | 113: b4 05 00 00 08 00 00 00 w5 = 8 ; for (i = 1; i < len; i++) | 114: 85 00 00 00 7e 00 00 00 call 126 112: 07 09 00 00 01 00 00 00 r9 += 1 | ; for (i = 1; i < len; i++) { 113: ad 89 09 00 00 00 00 00 if r9 < r8 goto +9 <LBB0_18> | 115: 25 08 02 00 6d 00 00 00 if r8 > 109 goto +2 <LBB0_21> > 116: 07 09 00 00 01 00 00 00 r9 += 1 > ; for (i = 1; i < len; i++) { > 117: ad 89 09 00 00 00 00 00 if r9 < r8 goto +9 <LBB0_17> ---8<---quoted
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+ BPF_SEQ_PRINTF(seq, "%c", + unix_sk->addr->name->sun_path[i] ?: + '@'); + } + } + + BPF_SEQ_PRINTF(seq, "\n"); + + return 0; +}diff --git a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h index 3af0998a0623..eef5646ddb19 100644 --- a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h +++ b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h@@ -5,6 +5,10 @@ #define AF_INET 2 #define AF_INET6 10 +#define __SO_ACCEPTCON (1 << 16) +#define UNIX_HASH_SIZE 256 +#define UNIX_ABSTRACT(unix_sk) (unix_sk->addr->hash < UNIX_HASH_SIZE) + #define SOL_TCP 6 #define TCP_CONGESTION 13 #define TCP_CA_NAME_MAX 16 --2.30.2