Re: [Xen-devel] [PATCH 1/2] misc: Replace zero-length arrays with flexible array member (automatic)

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 04/03/20 14:12, Philippe Mathieu-Daudé wrote:
> 
> hw/scsi/spapr_vscsi.c:69:29: error: field 'iu' with variable sized type
> 'union viosrp_iu' not at the end of a struct or class is a GNU extension
> [-Werror,-Wgnu-variable-sized-type-not-at-end]
>     union viosrp_iu         iu;
>                             ^
> 
> Yay we found a bug! Thanks Gustavo :)
> 
> union srp_iu {
>     struct srp_login_req login_req;
>     struct srp_login_rsp login_rsp;
>     struct srp_login_rej login_rej;
>     struct srp_i_logout i_logout;
>     struct srp_t_logout t_logout;
>     struct srp_tsk_mgmt tsk_mgmt;
>     struct srp_cmd cmd;
>     struct srp_rsp rsp;
>     uint8_t reserved[SRP_MAX_IU_LEN];
> };

It's variable-sized but it's okay as long as the total size doesn't
exceed SRP_MAX_IU_LEN.  So it's not a bug, but I agree it's a time bomb.
 Moving the field last should work, but it would still be quite
dangerous code.

Paolo


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