Dear BPF community, I am a student currently trying to use the BPF interface in the TCP congestion control study for faster Linux system integration without compiling the entire kernel. I've encountered a challenge while attempting to convert TCP BBR to BPF format and would greatly appreciate your guidance. My modifications to the original tcp_bbr is as follow: * change u8,u32,u64,etc to __u8, __u32, __u64, etc. * Defined external kernel functions * Removed compiler flags using macro (e.g., "unlikely", "READ_ONCE") * Borrowed some time definitions from bpf_cubic (e.g., HZ and JIFFY) * Defined constant values not included in vmlinux.h (e.g., "TCP_INFINITE_SSTHRESH") * Implemented do_div() and cmpxchg() from assembly to C * Changed min_t() macro to min() This is the link to my modified tcp_bbr file https://github.com/zmrui/bbr-bpf/blob/main/tcp_bbr.c I use "clang -O2 -target bpf -c -g bpf_cubic.c" command to compile and it doesn't output any warning or error, and the "sudo bpftool struct_ops register tcp_bbr.o" command does not have any output Then the "bpftool -debug" option displays the following debug message at the last line: "libbpf: sec '.rodata': failed to determine size from ELF: size 0, err -2" Additionally, the new algorithm doesn't appear in "net.ipv4.tcp_available_congestion_control" or in "bpftool struct_ops list". I did not find much related content for this debug error message on the Internet. I would be very grateful for any suggestions or insights you might have regarding this issue. Thank you in advance for your time and expertise. For context, here's my system information: Ubuntu 22.04 6.5.0-41-generic $ bpftool -V bpftool v7.3.0 using libbpf v1.3 features: llvm, skeletons -$ clang -v -Ubuntu clang version 14.0.0-1ubuntu1.1 Best, Mingrui
