linux-kernel - Re: [PATCH 1/2] dev/dax: fix uninitialized variable build warning

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Message-ID: <CAPcyv4gNYekwo1DQ9fOCzdtixvAUn5YnZY0wKfxQaeRppwdUPQ@mail.gmail.com>
Date:   Wed, 18 Oct 2017 08:56:48 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH 1/2] dev/dax: fix uninitialized variable build warning

On Wed, Oct 18, 2017 at 8:40 AM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> Fix this build warning:
>
> warning: 'phys' may be used uninitialized in this function
> [-Wuninitialized]
>
> As reported here:
>
> https://lkml.org/lkml/2017/10/16/152
>
> This should have no functional change because you can only get into the if
> statement in dax_pgoff_to_phys() that is complaining about 'phys' being
> uninitialized if you broke out early in the above loop, in which case
> 'phys' will be set.

Then the compiler is wrong.

>
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> ---
>  drivers/dax/device.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index e9f3b3e..4aca0a2 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -222,7 +222,7 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
>                 unsigned long size)
>  {
>         struct resource *res;
> -       phys_addr_t phys;
> +       phys_addr_t phys = 0;

We have uninitialized_var() for silencing the compiler, and since the
report is bogus we might note with a comment which gcc had a problem
with this routine.