Re: [PATCH] xfs_db: check on-disk structure sizes

[Brian Foster <bfoster@redhat.com>]

On Mon, Jan 11, 2016 at 03:46:44PM -0800, Darrick J. Wong wrote:
> Check on-disk structure sizes against known values.
> Use this to catch inadvertent changes in structure size due to padding
> and alignment issues, etc.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

What's the need for this in userspace? Not a big deal really, but it
seems like it serves the fundamental purpose sufficiently in the kernel.

That aside, this does fail if I tweak a structure size, though I don't
think I get the intended error. I end up with a linker error instead:

...
    [LD]     xfs_db
ondisk.o: In function `xfs_check_ondisk_structs':
/home/bfoster/repos/xfsprogs-dev/db/ondisk.c:26: undefined reference to `__compiletime_assert_26'
collect2: error: ld returned 1 exit status
../include/buildrules:45: recipe for target 'xfs_db' failed
gmake[3]: *** [xfs_db] Error 1
include/buildrules:35: recipe for target 'db' failed
gmake[2]: *** [db] Error 2
Makefile:70: recipe for target 'default' failed
make[1]: *** [default] Error 2
Makefile:68: recipe for target 'default' failed
make: *** [default] Error 2

This is with gcc 5.3.1. It works fine with the kernel patch so I don't
_think_ it's my environment, but I could be wrong...

Brian

>  db/Makefile         |    2 -
>  db/init.c           |    3 +
>  db/ondisk.c         |   63 +++++++++++++++++++++++
>  db/ondisk.h         |  139 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  libxfs/xfs_format.h |    4 +
>  5 files changed, 210 insertions(+), 1 deletion(-)
>  create mode 100644 db/ondisk.c
>  create mode 100644 db/ondisk.h
> 
> diff --git a/db/Makefile b/db/Makefile
> index 8260da3..ba3e942 100644
> --- a/db/Makefile
> +++ b/db/Makefile
> @@ -12,7 +12,7 @@ HFILES = addr.h agf.h agfl.h agi.h attr.h attrshort.h bit.h block.h bmap.h \
>  	dir2.h dir2sf.h dquot.h echo.h faddr.h field.h \
>  	flist.h fprint.h frag.h freesp.h hash.h help.h init.h inode.h input.h \
>  	io.h logformat.h malloc.h metadump.h output.h print.h quit.h sb.h \
> -	 sig.h strvec.h text.h type.h write.h attrset.h symlink.h
> +	 sig.h strvec.h text.h type.h write.h attrset.h symlink.h ondisk.h
>  CFILES = $(HFILES:.h=.c)
>  LSRCFILES = xfs_admin.sh xfs_ncheck.sh xfs_metadump.sh
>  
> diff --git a/db/init.c b/db/init.c
> index c0472c8..d6df093 100644
> --- a/db/init.c
> +++ b/db/init.c
> @@ -28,6 +28,7 @@
>  #include "output.h"
>  #include "malloc.h"
>  #include "type.h"
> +#include "ondisk.h"
>  
>  static char		**cmdline;
>  static int		ncmdline;
> @@ -60,6 +61,8 @@ init(
>  	struct xfs_buf	*bp;
>  	int		c;
>  
> +	xfs_check_ondisk_structs();
> +
>  	setlocale(LC_ALL, "");
>  	bindtextdomain(PACKAGE, LOCALEDIR);
>  	textdomain(PACKAGE);
> diff --git a/db/ondisk.c b/db/ondisk.c
> new file mode 100644
> index 0000000..532333d
> --- /dev/null
> +++ b/db/ondisk.c
> @@ -0,0 +1,63 @@
> +/*
> + * Copyright (c) 2016 Oracle.
> + * All Rights Reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> + */
> +
> +#include "libxfs.h"
> +#include "ondisk.h"
> +
> +void
> +xfs_check_ondisk_structs(void)
> +{
> +	/* on-disk structures */
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_dsb,			264);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_agf,			224);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_agi,			336);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_agfl,			36);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_timestamp,		8);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_dinode,		176);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_disk_dquot,		104);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_dqblk,			136);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_dsymlink_hdr,		56);
> +	XFS_CHECK_STRUCT_SIZE(xfs_alloc_rec_t,			8);
> +	XFS_CHECK_STRUCT_SIZE(xfs_alloc_key_t,			8);
> +	XFS_CHECK_STRUCT_SIZE(xfs_alloc_ptr_t,			4);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_inobt_rec,		16);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_inobt_key,		4);
> +	XFS_CHECK_STRUCT_SIZE(xfs_inobt_ptr_t,			4);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_bmdr_block,		4);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_bmbt_rec,		16);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_bmbt_key,		8);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_btree_block,		72);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_acl_entry,		12);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_acl,			4);
> +
> +	/* log structures */
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_trans_header,		16);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_inode_log_format_32,	52);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_inode_log_format_64,	56);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_ictimestamp,		8);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_icdinode,		176);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_extent_32,		12);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_extent_64,		16);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format_32,	28);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format_64,	32);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format_32,	28);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format_64,	32);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_dq_logformat,		24);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_qoff_logformat,	20);
> +	XFS_CHECK_STRUCT_SIZE(struct xfs_icreate_log,		28);
> +}
> diff --git a/db/ondisk.h b/db/ondisk.h
> new file mode 100644
> index 0000000..b5784d1
> --- /dev/null
> +++ b/db/ondisk.h
> @@ -0,0 +1,139 @@
> +/*
> + * Copyright (c) 2016 Oracle.
> + * All Rights Reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> + */
> +
> +#ifndef __XFS_DB_ONDISK_H
> +#define __XFS_DB_ONDISK_H
> +
> +/* Compile time object size, -1 for unknown */
> +#ifndef __compiletime_error
> +# define __compiletime_error(message)
> +/*
> + * Sparse complains of variable sized arrays due to the temporary variable in
> + * __compiletime_assert. Unfortunately we can't just expand it out to make
> + * sparse see a constant array size without breaking compiletime_assert on old
> + * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
> + */
> +# ifndef __CHECKER__
> +#  define __compiletime_error_fallback(condition) \
> +	do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
> +# endif
> +#endif
> +#ifndef __compiletime_error_fallback
> +# define __compiletime_error_fallback(condition) do { } while (0)
> +#endif
> +
> +#define __compiletime_assert(condition, msg, prefix, suffix)		\
> +	do {								\
> +		bool __cond = !(condition);				\
> +		extern void prefix ## suffix(void) __compiletime_error(msg); \
> +		if (__cond)						\
> +			prefix ## suffix();				\
> +		__compiletime_error_fallback(__cond);			\
> +	} while (0)
> +
> +#define _compiletime_assert(condition, msg, prefix, suffix) \
> +	__compiletime_assert(condition, msg, prefix, suffix)
> +
> +/**
> + * compiletime_assert - break build and emit msg if condition is false
> + * @condition: a compile-time constant condition to check
> + * @msg:       a message to emit if condition is false
> + *
> + * In tradition of POSIX assert, this macro will break the build if the
> + * supplied condition is *false*, emitting the supplied error message if the
> + * compiler has support to do so.
> + */
> +#define compiletime_assert(condition, msg) \
> +	_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> +
> +#ifdef __CHECKER__
> +#define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
> +#define BUILD_BUG_ON_ZERO(e) (0)
> +#define BUILD_BUG_ON_NULL(e) ((void*)0)
> +#define BUILD_BUG_ON_INVALID(e) (0)
> +#define BUILD_BUG_ON_MSG(cond, msg) (0)
> +#define BUILD_BUG_ON(condition) (0)
> +#define BUILD_BUG() (0)
> +#else /* __CHECKER__ */
> +
> +/* Force a compilation error if a constant expression is not a power of 2 */
> +#define BUILD_BUG_ON_NOT_POWER_OF_2(n)			\
> +	BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
> +
> +/* Force a compilation error if condition is true, but also produce a
> +   result (of value 0 and type size_t), so the expression can be used
> +   e.g. in a structure initializer (or where-ever else comma expressions
> +   aren't permitted). */
> +#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
> +#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
> +
> +/*
> + * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
> + * expression but avoids the generation of any code, even if that expression
> + * has side-effects.
> + */
> +#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
> +
> +/**
> + * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
> + *		      error message.
> + * @condition: the condition which the compiler should know is false.
> + *
> + * See BUILD_BUG_ON for description.
> + */
> +#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> +
> +/**
> + * BUILD_BUG_ON - break compile if a condition is true.
> + * @condition: the condition which the compiler should know is false.
> + *
> + * If you have some code which relies on certain constants being equal, or
> + * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
> + * detect if someone changes it.
> + *
> + * The implementation uses gcc's reluctance to create a negative array, but gcc
> + * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
> + * inline functions).  Luckily, in 4.3 they added the "error" function
> + * attribute just for this type of case.  Thus, we use a negative sized array
> + * (should always create an error on gcc versions older than 4.4) and then call
> + * an undefined function with the error attribute (should always create an
> + * error on gcc 4.3 and later).  If for some reason, neither creates a
> + * compile-time error, we'll still have a link-time error, which is harder to
> + * track down.
> + */
> +#ifndef __OPTIMIZE__
> +#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
> +#else
> +#define BUILD_BUG_ON(condition) \
> +	BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> +#endif
> +
> +/**
> + * BUILD_BUG - break compile if used.
> + *
> + * If you have some code that you expect the compiler to eliminate at
> + * build time, you should use BUILD_BUG to detect if it is
> + * unexpectedly used.
> + */
> +#define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
> +
> +#endif	/* __CHECKER__ */
> +
> +void xfs_check_ondisk_structs(void);
> +
> +#endif /* __XFS_DB_ONDISK_H */
> diff --git a/libxfs/xfs_format.h b/libxfs/xfs_format.h
> index a35009a..c4c0c1c 100644
> --- a/libxfs/xfs_format.h
> +++ b/libxfs/xfs_format.h
> @@ -1505,4 +1505,8 @@ struct xfs_acl {
>  #define SGI_ACL_FILE_SIZE	(sizeof(SGI_ACL_FILE)-1)
>  #define SGI_ACL_DEFAULT_SIZE	(sizeof(SGI_ACL_DEFAULT)-1)
>  
> +#define XFS_CHECK_STRUCT_SIZE(structname, size) \
> +	BUILD_BUG_ON_MSG(sizeof(structname) != (size), "XFS: sizeof(struct " \
> +		#structname ") is wrong, expected " #size)
> +
>  #endif /* __XFS_FORMAT_H__ */
> 
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