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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 23 Mar 2021 15:06:22 -0700
Message-ID: <CAKwvOdkBEQdVC73_datkwa+meitAGskDgTEr5LzX6AEnE4xd-w@mail.gmail.com>
Subject: Re: [PATCH] irqchip/gic-v3: fix OF_BAD_ADDR error handling
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Tue, Mar 23, 2021 at 6:18 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When building with extra warnings enabled, clang points out a
> mistake in the error handling:
>
> drivers/irqchip/irq-gic-v3-mbi.c:306:21: error: result of comparison of constant 18446744073709551615 with expression of type 'phys_addr_t' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]

Looks like based on CONFIG_PHYS_ADDR_T_64BIT, phys_addr_t can be u64
or u32, but of_translate_address always returns a u64.  This is fine
for the current value of OF_BAD_ADDR, but I think there's a risk of
losing the top 32b of the return value of of_translate_address() here?

>                 if (mbi_phys_base == OF_BAD_ADDR) {
>
> Truncate the constant to the same type as the variable it gets compared
> to, to shut make the check work and void the warning.
>
> Fixes: 505287525c24 ("irqchip/gic-v3: Add support for Message Based Interrupts as an MSI controller")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/irqchip/irq-gic-v3-mbi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3-mbi.c b/drivers/irqchip/irq-gic-v3-mbi.c
> index 563a9b366294..e81e89a81cb5 100644
> --- a/drivers/irqchip/irq-gic-v3-mbi.c
> +++ b/drivers/irqchip/irq-gic-v3-mbi.c
> @@ -303,7 +303,7 @@ int __init mbi_init(struct fwnode_handle *fwnode, struct irq_domain *parent)
>         reg = of_get_property(np, "mbi-alias", NULL);
>         if (reg) {
>                 mbi_phys_base = of_translate_address(np, reg);
> -               if (mbi_phys_base == OF_BAD_ADDR) {
> +               if (mbi_phys_base == (phys_addr_t)OF_BAD_ADDR) {
>                         ret = -ENXIO;
>                         goto err_free_mbi;
>                 }
> --
> 2.29.2
>


-- 
Thanks,
~Nick Desaulniers