[llvm-dev] bpf compilation using clang

[Sameeh Jubran via llvm-dev]

ping?
Who is maintaining bpf compilation
On Thu, Sep 13, 2018 at 12:58 PM Sameeh Jubran <sameeh at daynix.com> wrote:
>
> Hi all,
>
> I am trying to insert instructions into the bpf using the bpf syscall,
> the instructions were generated using the following command line:
>
> clang -I ~/Builds/bpf_rss/iproute2/include -Wall -target bpf -O2
> -emit-llvm -c upstream/qemu/hw/net/rss_tap_bpf_program.c -o - | llc
> -march=bpf -filetype=obj -o tap_bpf_program.o
>
> and then were translated to bpf instructions using the BPFCparser tool
>
> Every time I try to insert the array of instructions the verfier fails
> with the following error:
>
> back-edge from insn 363 to 364
>
> or something similar even though the compilation succeeds.
>
> I have multiple maps in my code and I translate only the code section
> to bpf insns structure and insert it using the bpf syscall as follows:
>
>     memset(&attr, 0, sizeof(attr));
>     attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
>     attr.insn_cnt = ARRAY_SIZE(l3_l4_hash_insns);
>     attr.insns = (__u64) (unsigned long) (l3_l4_hash_insns);
>     attr.license = (__u64) (unsigned long) ("Dual BSD/GPL");
>     attr.log_buf = (__u64) (unsigned long) (buffer);
>     attr.log_level = 7;
>     attr.log_size = BUFF_LEN;
>     attr.kern_version = 0;
>
>     ret = sys_bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
>
> I am not sure how to debug this error since the instructions are in
> binary and the precompiled source code doesn't seem to contain any
> weird loops or goto instructions...
>
> Is there a way to identify which line of source code is causing these errors?
>
> Thanks!



-- 
Respectfully,
Sameeh Jubran
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Software Engineer @ Daynix.