Unable to compile a simple "hello world" program to count ICMP message types

[shadyabhi]

New user to eBPF here. I'll really appreciate if someone can help me understand why this go generate is not using 64-bit libs?

➤ dnf repoquery -l glibc-devel |& grep stubs.h
/usr/include/bits/libm-simd-decl-stubs.h
/usr/include/gnu/stubs.h
/usr/include/bits/libm-simd-decl-stubs.h
/usr/include/gnu/stubs.h

➤ grep generate main.go
//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -target bpf icmp icmp_counter.c

>>>  0s elapsed...
➤ go generate
In file included from /home/arastogi/playground/icmp_counter/icmp_counter.c:4:
In file included from /usr/include/linux/icmp.h:23:
In file included from /usr/include/linux/if.h:28:
In file included from /usr/include/sys/socket.h:22:
In file included from /usr/include/features.h:514:
/usr/include/gnu/stubs.h:7:11: fatal error: 'gnu/stubs-32.h' file not found
# include <gnu/stubs-32.h>
          ^~~~~~~~~~~~~~~~
1 error generated.
Error: compile: exit status 1
exit status 1
main.go:14: running "go": exit status 1

>>>  0s elapsed...
➤

Full program for reference:-

#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <bpf/bpf_helpers.h>

struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __type(key, __u32);
    __type(value, __u64);
    __uint(max_entries, 256);
} icmp_count SEC(".maps");

SEC("xdp")
int count_icmp(struct xdp_md *ctx) {
    void *data = (void *)(long)ctx->data;
    void *data_end = (void *)(long)ctx->data_end;

    struct ethhdr *eth = data;
    if ((void*)(eth + 1) > data_end)
        return XDP_PASS;

    if (eth->h_proto != bpf_htons(ETH_P_IP))
        return XDP_PASS;

    struct iphdr *ip = (void*)(eth + 1);
    if ((void*)(ip + 1) > data_end)
        return XDP_PASS;

    if (ip->protocol != IPPROTO_ICMP)
        return XDP_PASS;

    struct icmphdr *icmp = (void*)(ip + 1);
    if ((void*)(icmp + 1) > data_end)
        return XDP_PASS;

    __u32 type = icmp->type;
    __u64 *count = bpf_map_lookup_elem(&icmp_count, &type);
    if (count)
        __sync_fetch_and_add(count, 1);

    return XDP_PASS;
}

char LICENSE[] SEC("license") = "Dual MIT/GPL";

[ti-mo]

This isn't really an issue with bpf2go, nor is it specifc to working with eBPF. As far as I can tell, this isn't an issue with your distribution either, since the headers look the same on my Arch machine. Welcome to the land of importing system headers! 🙂

Before I suggest anything else, let's take a look at the contents of that gnu/stubs.h file:

#if !defined __x86_64__
# include <gnu/stubs-32.h>
#endif
...

__x86_64__ isn't defined in your build env, so it tries to pick up a 32bit header. gnu/ is not a part of the kernel, so 32bit compat headers typically come in separate packages. I'll leave that up to you.

I briefly searched the Linux tree, and it does seems like this is a known issue when compiling bpf: https://github.com/torvalds/linux/blob/master/samples/bpf/gnu/stubs.h. Putting an empty stubs.h in your repo and adding it to your include paths could help things along. Or, if you want to change the behaviour of that ifdef, you can specify -D__x86_64__ to bpf2go using -cflags or after --. Normally, the compiler sets these based on the selected build target, but the bpf target doesn't do that by design.

Alternatively, when writing BPF it's often a good idea to simply copy struct definitions and such and put them in your own projects' header files (make sure to attribute GPL where needed!) to rule out external factors like these and to keep the complexity of the build setup manageable. After all, ICMP header definitions don't tend to change, if ever. :)

Hope this helps. Good luck!