Relocating BPF map fds

load.zig

    for (self.progs.items) |*prog| {
        const rel_name = try std.mem.join(self.allocator, "", &[_][]const u8{ ".rel", prog.name });
        defer self.allocator.free(rel_name);

        const rel_section: *Elf.Section = for (self.elf.relos.items) |relo| {
            if (mem.eql(u8, self.elf.get_section_name(relo), rel_name)) {
                break relo;
            }
        } else continue;

        for (std.mem.bytesAsSlice(Elf64_Rel, rel_section.data)) |relo| {
            const insn_idx = relo.r_offset / @sizeOf(BPF.Insn);
            const symbol = self.elf.get_sym_idx(@truncate(u32, relo.r_info >> 32));
            const map_name = self.elf.get_str(symbol.st_name);

            const map_fd = for (self.maps.items) |m| {
                if (mem.eql(u8, m.name, map_name)) {
                    break m.fd.?;
                }
            } else continue;

            prog.insns[insn_idx].src = BPF.PSEUDO_MAP_FD;
            prog.insns[insn_idx].imm = map_fd;
        }
    }