netdev - Re: [net-next 09/15] ixgbevf: Resolve truncation warning for q

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Date:   Thu, 1 Jun 2017 12:30:03 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net
Cc:     Tony Nguyen <anthony.l.nguyen@...el.com>, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com
Subject: Re: [net-next 09/15] ixgbevf: Resolve truncation warning for
 q_vector->name

Hello!

On 6/1/2017 12:19 AM, Jeff Kirsher wrote:

> From: Tony Nguyen <anthony.l.nguyen@...el.com>
>
> The following warning is now shown as a result of new checks added for
> gcc 7:
>
> drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c: In function ‘ixgbevf_open’:
> drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:1363:13: warning: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size between 3 and 18 [-Wformat-truncation=]
>       "%s-%s-%d", netdev->name, "TxRx", ri++);
>              ^~
> drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:1363:6: note: directive argument in the range [0, 2147483647]
>       "%s-%s-%d", netdev->name, "TxRx", ri++);
>       ^~~~~~~~~~
> drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:1362:4: note: ‘snprintf’ output between 8 and 32 bytes into a destination of size 24
>     snprintf(q_vector->name, sizeof(q_vector->name) - 1,
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       "%s-%s-%d", netdev->name, "TxRx", ri++);
>       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Resolve this warning by making a couple of changes.
>  - Don't reserve space for the null terminator.  Since snprintf adds the
>    null terminator automatically, there is no need for us to reserve a byte
>    for it.
>
>  - Change a couple variables that can never be negative from int to
>    unsigned int.
>
> While we're making changes to the format string, move the constant strings
> into the format string instead of providing them as specifiers.

    I suspect that trick saved some data space due to using the identical (and 
so merged) format strings...

> Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
> Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

[...]

MBR, Sergei