string is not stack allocated: not supported

[houminz]

Hi, I am trying to using cilium/ebpf to write ebpf program, and facing the problem of compiling.
The source code that I am writing is referred from this blog and its github. I am porting it to Go, and here is my code sockredir.

The compiling message shows that section "sockops": string is not stack allocated: not supported

go generate
Generating for amd64
Compiled /root/sockredir/sockredir_bpfel.o
Stripped /root/sockredir/sockredir_bpfel.o
Error: can't write /root/sockredir/sockredir_bpfel.go: can't load BPF from ELF: section "sockops": string is not stack allocated: not supported
exit status 1
main.go:18: running "go": exit status 1
make: *** [Makefile:15: BPFDemo] Error 1

//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -cc clang SockRedir ./bpf/sockops.c -- -I./bpf/headers

The ELF object has been generated, but go file is not.

When I remove the code below, the build is successful.

SEC("sockops")
int my_sockmap(struct bpf_sock_ops *skops)
{
    switch (skops->op) {
        case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
        case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
            if (skops->family == 2) { //AF_INET
                bpf_sock_ops_ipv4(skops);
            }
            break;
        default:
            break;
    }
    return 0;
}

I am wondering why shall we come across the error messages, since most of the code is brorrow from the repo and we could compile it using clang.

Any help would be appreciated, thanks.

[chenhengqi]

Your problem is in bpf_sock_ops_ipv4: https://github.com/SimpCosm/godemo/blob/c3d3ab845732d415e4de1df8077c395daa7703f9/sockredir/bpf/sockops.c#L61-L63

Replace bpf_trace_printk with bpf_printk. The latter is a macro that ensures that the format string is allocated on the stack.