linux-kernel - Re: Build regressions/improvements in v4.6-rc1

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Date:	Tue, 29 Mar 2016 06:16:17 +0000
From:	Mikael Starvik <mikael.starvik@...s.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
CC:	Dave Chinner <david@...morbit.com>, Rich Felker <dalias@...c.org>,
	linux-cris-kernel <linux-cris-kernel@...s.com>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>
Subject: Re: Build regressions/improvements in v4.6-rc1

I have not lookend at the structs but CRIS is a bit unusual since it does no alignment what so ever. If a short is followed by an int will be unaligned like in a packed struct.

Jesper or someone else will take a look at this specific issue.

/Mikael
> 29 mars 2016 kl. 00:47 skrev Darrick J. Wong <darrick.wong@...cle.com>:
> 
>> On Tue, Mar 29, 2016 at 08:59:23AM +1100, Dave Chinner wrote:
>>> On Sun, Mar 27, 2016 at 02:43:24PM +0200, Geert Uytterhoeven wrote:
>>> On Sun, Mar 27, 2016 at 2:39 PM, Geert Uytterhoeven
>>> <geert@...ux-m68k.org> wrote:
>>>> Below is the list of build error/warning regressions/improvements in
>>>> v4.6-rc1[1] compared to v4.5[2].
>>>> 
>>>> Summarized:
>>>>  - build errors: +9/-6
>>> 
>>>> [1] http://kisskb.ellerman.id.au/kisskb/head/10114/ (all 262 configs)
>>>> [2] http://kisskb.ellerman.id.au/kisskb/head/10047/ (all 262 configs)
>>> 
>>>> 9 error regressions:
>>>>  + /home/kisskb/slave/src/fs/xfs/xfs_ondisk.h: error: call to
>>>> '__compiletime_assert_79' declared with attribute error: XFS:
>>>> sizeof(xfs_attr_shortform_t) is wrong, expected 8:  => 79:2
>>> 
>>> cris-allyesconfig, cris-allmodconfig
>> 
>> Yup, cris is the only platform that throws this error on this
>> structure. It's an on-disk structure and relying on the gcc
>> optimiser to do the same thing from release to release has become
>> such a crap-shoot these days. Hence as a stop-gap measure we added
>> build time checking of what they compiler is doing with those
>> structures, and to refuse to build XFS if the compiler/platform is
>> doing something obviously different.
>> 
>> Modernising the on-disk structure definitions is on the list of
>> things to do, but it's nowhere near the top of my list at the
>> moment...
> 
> I have a test patch that (for now) changes the ondisk format checks for the
> variable-length structures to look at the offsets of the non-variable-length
> fields.  Can you give it a try?
> 
> (No idea if it fixes fixes cris, but it passes the six arches that I can
> actually test on (x86/power/arm)).  The downside is that it does nothing about
> troubling implication that there could be computers writing out a disk format
> that's incompatible with x86 XFSes...)
> 
> --D
> -----------
> From: Darrick J. Wong <darrick.wong@...cle.com>
> Subject: [PATCH] xfs: check offsets of variable length structures
> 
> Some of the directory/attr structures contain variable-length objects,
> so the enclosing structure doesn't have a meaningful fixed size at
> compile time.  We can check the offsets of the members before the
> variable-length member, so do those.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
> fs/xfs/xfs_ondisk.h |   25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h
> index 960648b..3742216 100644
> --- a/fs/xfs/xfs_ondisk.h
> +++ b/fs/xfs/xfs_ondisk.h
> @@ -22,6 +22,11 @@
>    BUILD_BUG_ON_MSG(sizeof(structname) != (size), "XFS: sizeof(" \
>        #structname ") is wrong, expected " #size)
> 
> +#define XFS_CHECK_OFFSET(structname, member, off) \
> +    BUILD_BUG_ON_MSG(offsetof(structname, member) != (off), \
> +        "XFS: offsetof(" #structname ", " #member ") is wrong, " \
> +        "expected " #off)
> +
> static inline void __init
> xfs_check_ondisk_structs(void)
> {
> @@ -81,15 +86,28 @@ xfs_check_ondisk_structs(void)
>    XFS_CHECK_STRUCT_SIZE(xfs_attr_leaf_name_remote_t,    12);
>     */
> 
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, valuelen,    0);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, namelen,    2);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, nameval,    3);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, valueblk,    0);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, valuelen,    4);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, namelen,    8);
> +    XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, name,    9);
>    XFS_CHECK_STRUCT_SIZE(xfs_attr_leafblock_t,        40);
> -    XFS_CHECK_STRUCT_SIZE(xfs_attr_shortform_t,        8);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, hdr.totsize,    0);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, hdr.count,    2);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].namelen,    4);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].valuelen, 5);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].flags,    6);
> +    XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].nameval,    7);
>    XFS_CHECK_STRUCT_SIZE(xfs_da_blkinfo_t,            12);
>    XFS_CHECK_STRUCT_SIZE(xfs_da_intnode_t,            16);
>    XFS_CHECK_STRUCT_SIZE(xfs_da_node_entry_t,        8);
>    XFS_CHECK_STRUCT_SIZE(xfs_da_node_hdr_t,        16);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_free_t,        4);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_hdr_t,        16);
> -    XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_unused_t,        6);
> +    XFS_CHECK_OFFSET(xfs_dir2_data_unused_t, freetag,    0);
> +    XFS_CHECK_OFFSET(xfs_dir2_data_unused_t, length,    2);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_free_hdr_t,        16);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_free_t,            16);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_ino4_t,            4);
> @@ -100,6 +118,9 @@ xfs_check_ondisk_structs(void)
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_leaf_t,            16);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_leaf_tail_t,        4);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_entry_t,        3);
> +    XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, namelen,        0);
> +    XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, offset,        1);
> +    XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, name,        3);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_hdr_t,        10);
>    XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_off_t,        2);
>