scsi: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language extension
to the C90 standard, but the preferred mechanism to declare variable-length
types such as these ones is a flexible array member[1][2], introduced in
C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning in
case the flexible array does not occur last in the structure, which will
help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by this
change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Link: https://lore.kernel.org/r/20200224161406.GA21454@embeddedor
Reviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Satish Kharat <satishkh@cisco.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index f146a4557787..579e24c92f2f 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -230,7 +230,7 @@ struct scsi_device {
 	struct mutex		state_mutex;
 	enum scsi_device_state sdev_state;
 	struct task_struct	*quiesced_by;
-	unsigned long		sdev_data[0];
+	unsigned long		sdev_data[];
 } __attribute__((aligned(sizeof(unsigned long))));
 
 #define	to_scsi_device(d)	\
@@ -314,7 +314,7 @@ struct scsi_target {
 	char			scsi_level;
 	enum scsi_target_state	state;
 	void 			*hostdata; /* available to low-level driver */
-	unsigned long		starget_data[0]; /* for the transport */
+	unsigned long		starget_data[]; /* for the transport */
 	/* starget_data must be the last element!!!! */
 } __attribute__((aligned(sizeof(unsigned long))));