Issue eBPF kernel programs with ldc?

[Alexander Zhirov]

On Sunday, 5 January 2025 at 14:17:29 UTC, data pulverizer wrote:
> ```d
> //hello_world.d
>
> @system:
> @nogc:
> extern(C):
>
> @(ldc.attributes.section("license")) __gshared 
> immutable(char)[3] LICENSE = "GPL";
>
> import core.stdc.stdlib;
> import core.stdc.stdarg;
> import ldc.attributes;
>
> long bpf_trace_printk(const(char)* fmt, uint fmt_size, ...);
> @(ldc.attributes.section("xdp_md")) struct xdp_md;
>
> @(ldc.attributes.section("xdp")) int xdp_prog(xdp_md* ctx)
> {
>     bpf_trace_printk("Hello, eBPF!\n", 14);
>     return 0;
> }
> ```

Just fix

```d
@system:
@nogc:
nothrow:
extern(C):

import ldc.attributes;

@(ldc.attributes.section("license"))
__gshared immutable(char)[4] LICENSE = "GPL\0";

struct xdp_md
{
     uint data;
     uint data_end;
     uint data_meta;
     uint ingress_ifindex;
     uint rx_queue_index;
     uint egress_ifindex;
}

enum int BPF_FUNC_trace_printk = 6;

alias BpfTracePrintk =
     extern(C) long function(const(char)* fmt, uint fmt_size, ...) 
@nogc nothrow;

enum BpfTracePrintk bpf_trace_printk = 
cast(BpfTracePrintk)BPF_FUNC_trace_printk;

enum int XDP_PASS = 2;

@(ldc.attributes.section("xdp"))
int xdp_prog(xdp_md* ctx)
{
     bpf_trace_printk("Hello, eBPF!\n", 14);
     return XDP_PASS;
}
```

Build:

```sh
ldc2 -c -O2 -release -betterC --nogc -fno-moduleinfo --march=bpf 
hello_world.d -of=hello_world_d.o
llvm-objcopy --remove-section .eh_frame --remove-section 
.rel.eh_frame hello_world_d.o
```