|
Recently, I saw a patch[1] on the ext4 mailing list regarding
the correction of a macro definition error. Jan mentioned
that "The bug in the macro is a really nasty trap...".
Because existing compilers are unable to detect
unused parameters in macro definitions. This inspired me
to write a script to check for unused parameters in
macro definitions and to run it.
Surprisingly, the script uncovered numerous issues across
various subsystems, including filesystems, drivers, and sound etc.
Some of these issues involved parameters that were accepted
but never used, for example:
#define XFS_DAENTER_DBS(mp,w) \
(XFS_DA_NODE_MAXDEPTH + (((w) == XFS_DATA_FORK) ? 2 : 0))
where mp was unused.
While others are actual bugs.
For example:
#define HAL_SEQ_WCSS_UMAC_CE0_SRC_REG(x) \
(ab->hw_params.regs->hal_seq_wcss_umac_ce0_src_reg)
#define HAL_SEQ_WCSS_UMAC_CE0_DST_REG(x) \
(ab->hw_params.regs->hal_seq_wcss_umac_ce0_dst_reg)
#define HAL_SEQ_WCSS_UMAC_CE1_SRC_REG(x) \
(ab->hw_params.regs->hal_seq_wcss_umac_ce1_src_reg)
#define HAL_SEQ_WCSS_UMAC_CE1_DST_REG(x) \
(ab->hw_params.regs->hal_seq_wcss_umac_ce1_dst_reg)
where x was entirely unused, and instead, a local variable ab was used.
I have submitted patches[2-5] to fix some of these issues,
but due to the large number, many still remain unaddressed.
I believe that the kernel and matainers would benefit from
this script to check for unused parameters in macro definitions.
It should be noted that it may cause some false positives
in conditional compilation scenarios, such as
#ifdef DEBUG
static int debug(arg) {};
#else
#define debug(arg)
#endif
So the caller needs to manually verify whether it is a true
issue. But this should be fine, because Maintainers should only
need to review their own subsystems, which typically results
in only a few reports.
[1]: https://patchwork.ozlabs.org/project/linux-ext4/patch/[email protected]/
[2]: https://lore.kernel.org/linux-xfs/[email protected]/
[3]: https://lore.kernel.org/linux-bcachefs/[email protected]/
[4]: https://sourceforge.net/p/linux-f2fs/mailman/message/58797811/
[5]: https://sourceforge.net/p/linux-f2fs/mailman/message/58797812/
[[email protected]: reduce false positives]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Julian Sun <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Junchao Sun <[email protected]>
Cc: Kalle Valo <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Nicolas Schier <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
|