scsi: aacraid: Replace one-element array with flexible-array member

There is a regular need in the kernel to provide a way to declare having a
dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member in struct
aac_raw_io2 instead of one-element array, and use the struct_size() helper.

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warnings:

drivers/scsi/aacraid/aachba.c: In function ‘aac_build_sgraw2’:
drivers/scsi/aacraid/aachba.c:3970:18: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
3970 | if (rio2->sge[j].length % (i*PAGE_SIZE)) {
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:3974:27: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
3974 | nseg_new += (rio2->sge[j].length / (i*PAGE_SIZE));
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4011:28: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4011 | for (j = 0; j < rio2->sge[i].length / (pages * PAGE_SIZE); ++j) {
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4012:24: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4012 | addr_low = rio2->sge[i].addrLow + j * pages * PAGE_SIZE;
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4014:33: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4014 | sge[pos].addrHigh = rio2->sge[i].addrHigh;
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4015:28: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4015 | if (addr_low < rio2->sge[i].addrLow)
| ~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Link: https://lore.kernel.org/lkml/[e-mail]/
Link: https://lore.kernel.org/r/20210421185611.GA105224@embeddedor
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>
Build-tested-by: kernel test robot <[e-mail]>

drivers/scsi/aacraid/aachba.c

···
 		if (ret < 0)
 			return ret;
 		command = ContainerRawIo2;
-		fibsize = sizeof(struct aac_raw_io2) +
-			((le32_to_cpu(readcmd2->sgeCnt)-1) * sizeof(struct sge_ieee1212));
+		fibsize = struct_size(readcmd2, sge,
+				     le32_to_cpu(readcmd2->sgeCnt));
 	} else {
 		struct aac_raw_io *readcmd;
 		readcmd = (struct aac_raw_io *) fib_data(fib);
···
 		if (ret < 0)
 			return ret;
 		command = ContainerRawIo2;
-		fibsize = sizeof(struct aac_raw_io2) +
-			((le32_to_cpu(writecmd2->sgeCnt)-1) * sizeof(struct sge_ieee1212));
+		fibsize = struct_size(writecmd2, sge,
+				      le32_to_cpu(writecmd2->sgeCnt));
 	} else {
 		struct aac_raw_io *writecmd;
 		writecmd = (struct aac_raw_io *) fib_data(fib);
···
 	if (aac_convert_sgl == 0)
 		return 0;
 
-	sge = kmalloc_array(nseg_new, sizeof(struct sge_ieee1212), GFP_ATOMIC);
+	sge = kmalloc_array(nseg_new, sizeof(*sge), GFP_ATOMIC);
 	if (sge == NULL)
 		return -ENOMEM;
 

drivers/scsi/aacraid/aacraid.h

···
 	u8		bpComplete;	/* reserved for F/W use */
 	u8		sgeFirstIndex;	/* reserved for F/W use */
 	u8		unused[4];
-	struct sge_ieee1212	sge[1];
+	struct sge_ieee1212	sge[];
 };
 
 #define CT_FLUSH_CACHE 129