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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 1 Apr 2021 12:05:53 -0700
Message-ID: <CAKwvOdkCe1OkPetLzFTO+f-dp8=kD3OKX8mfEnw2GBRkU_cBnw@mail.gmail.com>
Subject: Re: [PATCH] ARM: OMAP: Fix use of possibly uninitialized irq variable
To:     Maciej Falkowski <maciej.falkowski9@gmail.com>
Cc:     khilman@kernel.org, aaro.koskinen@iki.fi, tony@atomide.com,
        Russell King <linux@armlinux.org.uk>,
        linux-omap@vger.kernel.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Thu, Apr 1, 2021 at 9:12 AM Maciej Falkowski
<maciej.falkowski9@gmail.com> wrote:
>
> The current control flow of IRQ number assignment to `irq` variable
> allows a request of IRQ of unspecified value,
> generating a warning under Clang compilation with omap1_defconfig on linux-next:
>
> arch/arm/mach-omap1/pm.c:656:11: warning: variable 'irq' is used uninitialized whenever
> 'if' condition is false [-Wsometimes-uninitialized]
>         else if (cpu_is_omap16xx())
>                  ^~~~~~~~~~~~~~~~~
> ./arch/arm/mach-omap1/include/mach/soc.h:123:30: note: expanded from macro 'cpu_is_omap16xx'
>                                         ^~~~~~~~~~~~~
> arch/arm/mach-omap1/pm.c:658:18: note: uninitialized use occurs here
>         if (request_irq(irq, omap_wakeup_interrupt, 0, "peripheral wakeup",
>                         ^~~
> arch/arm/mach-omap1/pm.c:656:7: note: remove the 'if' if its condition is always true
>         else if (cpu_is_omap16xx())
>              ^~~~~~~~~~~~~~~~~~~~~~
> arch/arm/mach-omap1/pm.c:611:9: note: initialize the variable 'irq' to silence this warning
>         int irq;
>                ^
>                 = 0
> 1 warning generated.

Ooh, yeah if cpu_is_omap15xx() then irq is unused uninitialized; I
don't see any INT_1610_WAKE_UP_REQ-equlivalent for
INT_15XX_WAKE_UP_REQ.

Ok, LGTM.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

I agree with Nathan on the Fixes tag.

>
> The patch provides a default value to the `irq` variable
> along with a validity check.
>
> Signed-off-by: Maciej Falkowski <maciej.falkowski9@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1324
> ---
>  arch/arm/mach-omap1/pm.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/mach-omap1/pm.c b/arch/arm/mach-omap1/pm.c
> index 2c1e2b32b9b3..a745d64d4699 100644
> --- a/arch/arm/mach-omap1/pm.c
> +++ b/arch/arm/mach-omap1/pm.c
> @@ -655,9 +655,13 @@ static int __init omap_pm_init(void)
>                 irq = INT_7XX_WAKE_UP_REQ;
>         else if (cpu_is_omap16xx())
>                 irq = INT_1610_WAKE_UP_REQ;
> -       if (request_irq(irq, omap_wakeup_interrupt, 0, "peripheral wakeup",
> -                       NULL))
> -               pr_err("Failed to request irq %d (peripheral wakeup)\n", irq);
> +       else
> +               irq = -1;
> +
> +       if (irq >= 0) {
> +               if (request_irq(irq, omap_wakeup_interrupt, 0, "peripheral wakeup", NULL))
> +                       pr_err("Failed to request irq %d (peripheral wakeup)\n", irq);
> +       }
>
>         /* Program new power ramp-up time
>          * (0 for most boards since we don't lower voltage when in deep sleep)
> --
-- 
Thanks,
~Nick Desaulniers