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Re: [virt-tools-list] [osinfo PATCH] Mark the volume descriptor structs as packed



On Fri, Jan 06, 2012 at 04:35:09PM +0400, Christophe Fergeau wrote:
> This tells gcc it shouldn't add some padding between the struct
> members. which is important because we rely on this structure size
> being exactly 2048. One of its members is guint8 ignored2[246]; (only
> a 2 byte multiple) so all the fields of the struct won't be aligned
> on a 8 byte boundary, so gcc could do some unexpected things on
> some arch.
> The 2 structs changed by this patch only use arrays whose elements have
> the same size as chars so gcc will probably don't try to change their
> alignment, but one never knows..
> ---
>  osinfo/osinfo_media.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/osinfo/osinfo_media.c b/osinfo/osinfo_media.c
> index 2366993..15d6abe 100644
> --- a/osinfo/osinfo_media.c
> +++ b/osinfo/osinfo_media.c
> @@ -44,14 +44,14 @@ struct _PrimaryVolumeDescriptor {
>      guint8 ignored2[246];
>      gchar  publisher[MAX_PUBLISHER]; /* Publisher ID */
>      guint8 ignored3[1602];
> -};
> +} __attribute__ ((packed));
>  
>  typedef struct _SupplementaryVolumeDescriptor SupplementaryVolumeDescriptor;
>  
>  struct _SupplementaryVolumeDescriptor {
>      guint8 ignored[7];
>      gchar  system[MAX_SYSTEM]; /* System ID */
> -};
> +} __attribute__ ((packed));
>  
>  typedef struct _CreateFromLocationAsyncData CreateFromLocationAsyncData;
>  struct _CreateFromLocationAsyncData {

ACK

Daniel
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