linux-kernel - [PATCH 13/15] scsi: sas: avoid gcc-10 zero-length-bounds warning

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Date:   Thu, 30 Apr 2020 23:30:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        James Bottomley <James.Bottomley@...elEye.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>, linux-scsi@...r.kernel.org
Subject: [PATCH 13/15] scsi: sas: avoid gcc-10 zero-length-bounds warning

Two files access the zero-length resp_data[] array, which now
causes a compiler warning:

drivers/scsi/aic94xx/aic94xx_tmf.c: In function 'asd_get_tmf_resp_tasklet':
drivers/scsi/aic94xx/aic94xx_tmf.c:291:22: warning: array subscript 3 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[0]'} [-Wzero-length-bounds]
  291 |   res = ru->resp_data[3];
      |         ~~~~~~~~~~~~~^~~
In file included from include/scsi/libsas.h:15,
                 from drivers/scsi/aic94xx/aic94xx.h:16,
                 from drivers/scsi/aic94xx/aic94xx_tmf.c:11:
include/scsi/sas.h:557:9: note: while referencing 'resp_data'
  557 |  u8     resp_data[0];
      |         ^~~~~~~~~
drivers/scsi/libsas/sas_task.c: In function 'sas_ssp_task_response':
drivers/scsi/libsas/sas_task.c:21:30: warning: array subscript 3 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[0]'} [-Wzero-length-bounds]
   21 |   tstat->stat = iu->resp_data[3];
      |                 ~~~~~~~~~~~~~^~~
In file included from include/scsi/scsi_transport_sas.h:8,
                 from drivers/scsi/libsas/sas_internal.h:14,
                 from drivers/scsi/libsas/sas_task.c:3:
include/scsi/sas.h:557:9: note: while referencing 'resp_data'
  557 |  u8     resp_data[0];
      |         ^~~~~~~~~

This should really be a flexible-array member, but the structure
already has such a member, swapping it out with sense_data[] would
cause many more warnings elsewhere.

As a workaround, add a temporary pointer that can be accessed without
a warning.

Fixes: 2908d778ab3e ("[SCSI] aic94xx: new driver")
Fixes: 366ca51f30de ("[SCSI] libsas: abstract STP task status into a function")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/scsi/aic94xx/aic94xx_tmf.c | 4 +++-
 drivers/scsi/libsas/sas_task.c     | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/aic94xx/aic94xx_tmf.c b/drivers/scsi/aic94xx/aic94xx_tmf.c
index f814026f26fa..a3139f9766c8 100644
--- a/drivers/scsi/aic94xx/aic94xx_tmf.c
+++ b/drivers/scsi/aic94xx/aic94xx_tmf.c
@@ -269,6 +269,7 @@ static int asd_get_tmf_resp_tasklet(struct asd_ascb *ascb,
 	struct ssp_frame_hdr *fh;
 	struct ssp_response_iu   *ru;
 	int res = TMF_RESP_FUNC_FAILED;
+	u8 *resp;
 
 	ASD_DPRINTK("tmf resp tasklet\n");
 
@@ -287,8 +288,9 @@ static int asd_get_tmf_resp_tasklet(struct asd_ascb *ascb,
 	fh = edb->vaddr + 16;
 	ru = edb->vaddr + 16 + sizeof(*fh);
 	res = ru->status;
+	resp = ru->resp_data;
 	if (ru->datapres == 1)	  /* Response data present */
-		res = ru->resp_data[3];
+		res = resp[3];
 #if 0
 	ascb->tag = fh->tag;
 #endif
diff --git a/drivers/scsi/libsas/sas_task.c b/drivers/scsi/libsas/sas_task.c
index e2d42593ce52..4cd2f9611c4a 100644
--- a/drivers/scsi/libsas/sas_task.c
+++ b/drivers/scsi/libsas/sas_task.c
@@ -12,13 +12,14 @@ void sas_ssp_task_response(struct device *dev, struct sas_task *task,
 			   struct ssp_response_iu *iu)
 {
 	struct task_status_struct *tstat = &task->task_status;
+	u8 *resp = iu->resp_data;
 
 	tstat->resp = SAS_TASK_COMPLETE;
 
 	if (iu->datapres == 0)
 		tstat->stat = iu->status;
 	else if (iu->datapres == 1)
-		tstat->stat = iu->resp_data[3];
+		tstat->stat = resp[3];
 	else if (iu->datapres == 2) {
 		tstat->stat = SAM_STAT_CHECK_CONDITION;
 		tstat->buf_valid_size =
-- 
2.26.0