Re: [PATCH 05/76] libxfs: pack the agfl header structure so XFS_AGFL_SIZE is correct

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Sat, Dec 19, 2015 at 12:56:55AM -0800, Darrick J. Wong wrote:
> Because struct xfs_agfl is 36 bytes long and has a 64-bit integer
> inside it, gcc will quietly round the structure size up to the nearest
> 64 bits -- in this case, 40 bytes.  This results in the XFS_AGFL_SIZE
> macro returning incorrect results for v5 filesystems on 64-bit
> machines (118 items instead of 119).  As a result, a 32-bit xfs_repair
> will see garbage in AGFL item 119 and complain.
> 
> Therefore, tell gcc not to pad the structure so that the AGFL size
> calculation is correct.

Do you have a testcase for this?