linux-kernel - RE: [Intel-wired-lan] [PATCH] iavf: Use printf instead of gnu_printf for iavf_debug

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Message-ID: <26D9FDECA4FBDD4AADA65D8E2FC68A4A1D353FD7@ORSMSX104.amr.corp.intel.com>
Date:   Wed, 30 Jan 2019 18:20:12 +0000
From:   "Bowers, AndrewX" <andrewx.bowers@...el.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
Subject: RE: [Intel-wired-lan] [PATCH] iavf: Use printf instead of
 gnu_printf for iavf_debug_d

> -----Original Message-----
> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@...osl.org] On
> Behalf Of Nathan Chancellor
> Sent: Wednesday, January 9, 2019 8:22 PM
> To: Kirsher, Jeffrey T <jeffrey.t.kirsher@...el.com>
> Cc: netdev@...r.kernel.org; Nick Desaulniers <ndesaulniers@...gle.com>;
> linux-kernel@...r.kernel.org; Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com>; intel-wired-lan@...ts.osuosl.org;
> Nathan Chancellor <natechancellor@...il.com>; David S. Miller
> <davem@...emloft.net>
> Subject: [Intel-wired-lan] [PATCH] iavf: Use printf instead of gnu_printf for
> iavf_debug_d
> 
> Clang warns:
> 
> In file included from drivers/net/ethernet/intel/iavf/iavf_main.c:4:
> In file included from drivers/net/ethernet/intel/iavf/iavf.h:37:
> In file included from drivers/net/ethernet/intel/iavf/iavf_type.h:8:
> drivers/net/ethernet/intel/iavf/iavf_osdep.h:49:18: warning: 'format'
> attribute argument not supported: gnu_printf [-Wignored-attributes]
>         __attribute__ ((format(gnu_printf, 3, 4)));
>                         ^
> 1 warning generated.
> 
> We can convert from gnu_printf to printf without any side effects for two
> reasons:
> 
> 1. All iavf_debug instances use standard printf formats, as pointed out
>    by Miguel Ojeda at the below link, meaning gnu_printf is not strictly
>    required.
> 
> 2. However, GCC has aliased printf to gnu_printf on Linux since at least
>    2010 based on git history.
> 
>    From gcc/c-family/c-format.c:
> 
>    /* Attributes such as "printf" are equivalent to those such as
>       "gnu_printf" unless this is overridden by a target.  */
>    static const target_ovr_attr gnu_target_overrides_format_attributes[] =
>    {
>      { "gnu_printf",   "printf" },
>      { "gnu_scanf",    "scanf" },
>      { "gnu_strftime", "strftime" },
>      { "gnu_strfmon",  "strfmon" },
>      { NULL,           NULL }
>    };
> 
> The mentioned override only happens on Windows (mingw32). Changing
> from gnu_printf to printf is a no-op for GCC and stops Clang from warning.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/111
> Suggested-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/net/ethernet/intel/iavf/iavf_osdep.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Tested-by: Andrew Bowers <andrewx.bowers@...el.com>