On Thu, 28 Feb 2019, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
>
This switch case is already marked. So I think the patch description
should state that this patch is actually a workaround for a gcc deficiency
which prevents it from locating the marker.
> This patch fixes the following warning:
>
> In file included from drivers/scsi/dmx3191d.c:48:
> drivers/scsi/NCR5380.c: In function ?NCR5380_information_transfer?:
> drivers/scsi/NCR5380.c:1933:9: warning: this statement may fall through
> [-Wimplicit-fallthrough=]
> if (!hostdata->connected)
> ^
> drivers/scsi/NCR5380.c:1937:5: note: here
> default:
> ^~~~~~~
>
> Warning level 3 was used: -Wimplicit-fallthrough=3
>
> Notice that, in this particular case, the code comment is modified
> in accordance with what GCC is expecting to find.
>
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
>
> Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
> ---
> Changes in v2:
> - Update commit log.
> - Move code comment after the default label and
> retain reason for fall-through in comment as
> requested by Michael Schmitz.
>
> drivers/scsi/NCR5380.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/scsi/NCR5380.c b/drivers/scsi/NCR5380.c
> index 01c23d27f290..985d1c053578 100644
> --- a/drivers/scsi/NCR5380.c
> +++ b/drivers/scsi/NCR5380.c
> @@ -1933,13 +1933,12 @@ static void NCR5380_information_transfer(struct
> Scsi_Host *instance)
> if (!hostdata->connected)
> return;
>
> - /* Fall through to reject message */
> -
> + /* Fall through - to reject message */
This new hyphen is wrong and harms readability for humans.
I did confirm that gcc can be appeased by the use of a hyphen but not by
correct grammar such as "Fall through to reject message" or "Fall through.
Reject message."
> + default:
> /*
> - * If we get something weird that we
> aren't expecting,
> - * reject it.
> + * If we get something weird that we
> + * aren't expecting, reject it.
This reformatting isn't relevant to this patch. The comments can be
improved however (see below).
> */
> - default:
Moving the 'default' keyword closer to the 'fall through' comment makes
sense to me -- I could understand if gcc had simple, unambiguous rules for
annotations.
Do compilers and static analysers agree as to what a correctly annotated
switch label should look like? If not, we would have to try to mangle code
and comments in such a way that might satisfy all of the failings in all
of the tools.
> if (tmp == EXTENDED_MESSAGE)
> scmd_printk(KERN_INFO, cmd,
> "rejecting unknown
> extended message code %02x, length %d\n",
>
Here's an alternative patch, which has the virtue that a simple heuristic
will work. This patch does not require that other static analysis tools
will follow gcc's weird rules about hyphens. (I assume they don't but I
didn't check.)
diff --git a/drivers/scsi/NCR5380.c b/drivers/scsi/NCR5380.c
index 7fed9bb72784..fe0535affc14 100644
--- a/drivers/scsi/NCR5380.c
+++ b/drivers/scsi/NCR5380.c
@@ -1932,13 +1932,13 @@ static void NCR5380_information_transfer(struct
Scsi_Host *instance)
if (!hostdata->connected)
return;
- /* Fall through to reject message */
-
+ /* Reject message */
+ /* Fall through */
+ default:
/*
* If we get something weird that we
aren't expecting,
- * reject it.
+ * log it.
*/
- default:
if (tmp == EXTENDED_MESSAGE)
scmd_printk(KERN_INFO, cmd,
"rejecting unknown
extended message code %02x, length %d\n",
--
