linux-kernel - [PATCH] scsi: pm8001: avoid -Wrestrict warning

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Date:   Tue, 23 Mar 2021 13:54:23 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Jack Wang <jinpu.wang@...ud.ionos.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Viswas G <Viswas.G@...rochip.com>,
        Ruksar Devadi <Ruksar.devadi@...rochip.com>,
        Joe Perches <joe@...ches.com>,
        Vaibhav Gupta <vaibhavgupta40@...il.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Lee Jones <lee.jones@...aro.org>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] scsi: pm8001: avoid -Wrestrict warning

From: Arnd Bergmann <arnd@...db.de>

On some configurations, gcc warns about overlapping source and
destination arguments to snprintf:

drivers/scsi/pm8001/pm8001_init.c: In function 'pm8001_request_msix':
drivers/scsi/pm8001/pm8001_init.c:977:3: error: 'snprintf' argument 4 may overlap destination object 'pm8001_ha' [-Werror=restrict]
  977 |   snprintf(drvname, len, "%s-%d", pm8001_ha->name, i);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/pm8001/pm8001_init.c:962:56: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
  962 | static u32 pm8001_request_msix(struct pm8001_hba_info *pm8001_ha)
      |                                ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~

I first assumed this was a gcc bug, as that should not happen, but
a reduced test case makes it clear that this happens when the loop
counter is not bounded by the array size.

Help the compiler out by adding an explicit limit here to make the
code slightly more robust and avoid the warning.

Link: https://godbolt.org/z/6T1qPM
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/scsi/pm8001/pm8001_init.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/pm8001/pm8001_init.c b/drivers/scsi/pm8001/pm8001_init.c
index bd626ef876da..a268c647b987 100644
--- a/drivers/scsi/pm8001/pm8001_init.c
+++ b/drivers/scsi/pm8001/pm8001_init.c
@@ -963,6 +963,7 @@ static u32 pm8001_request_msix(struct pm8001_hba_info *pm8001_ha)
 {
 	u32 i = 0, j = 0;
 	int flag = 0, rc = 0;
+	int nr_irqs = pm8001_ha->number_of_intr;
 
 	if (pm8001_ha->chip_id != chip_8001)
 		flag &= ~IRQF_SHARED;
@@ -971,7 +972,10 @@ static u32 pm8001_request_msix(struct pm8001_hba_info *pm8001_ha)
 		   "pci_enable_msix request number of intr %d\n",
 		   pm8001_ha->number_of_intr);
 
-	for (i = 0; i < pm8001_ha->number_of_intr; i++) {
+	if (nr_irqs > ARRAY_SIZE(pm8001_ha->intr_drvname))
+		nr_irqs = ARRAY_SIZE(pm8001_ha->intr_drvname);
+
+	for (i = 0; i < nr_irqs; i++) {
 		snprintf(pm8001_ha->intr_drvname[i],
 			sizeof(pm8001_ha->intr_drvname[0]),
 			"%s-%d", pm8001_ha->name, i);
-- 
2.29.2