Re: [PATCH v2] scsi: NCR5380: Mark expected switch fall-through
From: Michael Schmitz
Date: Thu Feb 28 2019 - 20:32:39 EST
Finn's version looks fine to me.
Cheers,
ÂÂÂ Michael
On 1/03/19 2:16 PM, Finn Thain wrote:
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 <gustavo@xxxxxxxxxxxxxx>
---
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",