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

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Date:   Wed, 24 Mar 2021 11:56:39 +0100
From:   Jinpu Wang <jinpu.wang@...os.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Jack Wang <jinpu.wang@...ud.ionos.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        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 Mailinglist <linux-scsi@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi: pm8001: avoid -Wrestrict warning

On Tue, Mar 23, 2021 at 1:55 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> 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>
Acked-by: Jack Wang <jinpu.wang@...os.com>
> ---
>  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
>