linux-kernel - Re: fs/xfs/xfs_ondisk.h:96:2: error: call to '__compiletime_assert_96' declared with attribute error: XFS: sizeof(xfs_dir2_sf_entry

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Message-ID: <20161016164556.GA30222@infradead.org>
Date:   Sun, 16 Oct 2016 09:45:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     kbuild test robot <fengguang.wu@...el.com>, jonas@...thpole.se
Cc:     Dave Chinner <david@...morbit.com>, kbuild-all@...org,
        linux-kernel@...r.kernel.org
Subject: Re: fs/xfs/xfs_ondisk.h:96:2: error: call to
 '__compiletime_assert_96' declared with attribute error: XFS:
 sizeof(xfs_dir2_sf_entry_t) is wrong, expected 3

> head:   1001354ca34179f3db924eb66672442a173147dc

That's Linux 4.9-rc1

> 30cbc591 Darrick J. Wong 2016-03-09 @86  	XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_unused_t,		6);

But that's not how xfs_ondisk.h in 4.9-rc1 looks like

> 30cbc591 Darrick J. Wong 2016-03-09 @96  	XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_entry_t,		3);

And that's line 119.

Something is odd about this report. 

But both xfs_dir2_data_unused_t and xfs_dir2_sf_entry_t have one thing in
common: they are strutures that aren't padded to a natural alignment at
the end.  It seems like the openrisc gcc does implicit padding for them,
which sounds like a nightmware waiting to happen for any sort of disk
or network structure, so I'm really not sure if we should work around
it in xfs.