Re: How to add a -W flag in local Makefile

On Thu, Apr 18, 2024 at 03:27:13PM +0000, Wei Hu wrote:
> I added something like:
> 
> diff --git a/sys/dev/hyperv/vmbus/vmbus_var.h b/sys/dev/hyperv/vmbus/vmbus_var.h
> index b598f782947e..6e3b7b040827 100644
> --- a/sys/dev/hyperv/vmbus/vmbus_var.h
> +++ b/sys/dev/hyperv/vmbus/vmbus_var.h
> @@ -193,4 +193,17 @@ struct hyperv_tlb_flush {
> uint64_t        hv_vm_tlb_flush(pmap_t pmap, vm_offset_t addr1,
>                                 vm_offset_t addr2, cpuset_t mask);
> 
> +struct hv_vpset {
> +       uint64_t format;
> +       uint64_t valid_bank_mask;
> +       uint64_t bank_contents[];
> +} __packed;
> +
> +struct hv_tlb_flush_ex {
> +       uint64_t address_space;
> +       uint64_t flags;
> +       struct hv_vpset hv_vp_set;
> +       uint64_t gva_list[];
> +} __packed;
> +
> #endif /* !_VMBUS_VAR_H_ */
> 
> So, the struct hv_vpset is the second last member of struct hv_tlb_flush_ex. The member bank_contents[] in struct hv_vpset is of variable length. This would makes the last two members of struct hv_tlb_flush_ex both variable length. Therefore, the flag '-Wno-gnu-variable-sized-type-not-at-end' is needed, otherwise it would complain about this with errors like:
> 
No, the compiler' complain is correct.  The structure definition for
hv_tlb_flush_ex does not make sense: you never can access gva_list (except
for the case of bank_contents being zero-sized).