iavf: Use printf instead of gnu_printf for iavf_debug_d

Message ID 20190110042157.8445-1-natechancellor@gmail.com
State Under Review
Delegated to: Jeff Kirsher
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Series
  • iavf: Use printf instead of gnu_printf for iavf_debug_d
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Commit Message

Nathan Chancellor Jan. 10, 2019, 4:21 a.m.
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@gmail.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 drivers/net/ethernet/intel/iavf/iavf_osdep.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Nick Desaulniers Jan. 10, 2019, 6:54 p.m. | #1
On Wed, Jan 9, 2019 at 8:22 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> 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.

Thanks for this fix!
FWIW, using godbolt to see which version something was added in is
better than giving a year of the commit.  I don't think it matters for
this case, as the kernel already makes use of `printf` as you do in
this change, but food for thought for next time.

>
>    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@gmail.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  drivers/net/ethernet/intel/iavf/iavf_osdep.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/iavf/iavf_osdep.h b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> index e6e0b0328706..c90cafb526d0 100644
> --- a/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> +++ b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> @@ -46,7 +46,7 @@ struct iavf_virt_mem {
>
>  #define iavf_debug(h, m, s, ...)  iavf_debug_d(h, m, s, ##__VA_ARGS__)
>  extern void iavf_debug_d(void *hw, u32 mask, char *fmt_str, ...)
> -       __attribute__ ((format(gnu_printf, 3, 4)));
> +       __printf(3, 4);

And you make use of the __attribute__ wrapper from
include/linux/compiler_attributes.h, cool.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Nathan Chancellor Jan. 10, 2019, 7:07 p.m. | #2
On Thu, Jan 10, 2019 at 10:54:46AM -0800, Nick Desaulniers wrote:
> On Wed, Jan 9, 2019 at 8:22 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > 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.
> 
> Thanks for this fix!
> FWIW, using godbolt to see which version something was added in is
> better than giving a year of the commit.  I don't think it matters for
> this case, as the kernel already makes use of `printf` as you do in
> this change, but food for thought for next time.
> 

Yes that is a good point, I need to be taking advantage of that site
more.

Thank you for the review!
Nathan

> >
> >    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@gmail.com>
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >  drivers/net/ethernet/intel/iavf/iavf_osdep.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/intel/iavf/iavf_osdep.h b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> > index e6e0b0328706..c90cafb526d0 100644
> > --- a/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> > +++ b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
> > @@ -46,7 +46,7 @@ struct iavf_virt_mem {
> >
> >  #define iavf_debug(h, m, s, ...)  iavf_debug_d(h, m, s, ##__VA_ARGS__)
> >  extern void iavf_debug_d(void *hw, u32 mask, char *fmt_str, ...)
> > -       __attribute__ ((format(gnu_printf, 3, 4)));
> > +       __printf(3, 4);
> 
> And you make use of the __attribute__ wrapper from
> include/linux/compiler_attributes.h, cool.
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> 
> -- 
> Thanks,
> ~Nick Desaulniers
Miguel Ojeda Jan. 16, 2019, 10:38 p.m. | #3
Hi Nathan,

On Thu, Jan 10, 2019 at 5:22 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> 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@gmail.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

I forgot, in case you wanted it:

    Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

Thanks for taking care of writing the patch!

Cheers,
Miguel

Patch

diff --git a/drivers/net/ethernet/intel/iavf/iavf_osdep.h b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
index e6e0b0328706..c90cafb526d0 100644
--- a/drivers/net/ethernet/intel/iavf/iavf_osdep.h
+++ b/drivers/net/ethernet/intel/iavf/iavf_osdep.h
@@ -46,7 +46,7 @@  struct iavf_virt_mem {
 
 #define iavf_debug(h, m, s, ...)  iavf_debug_d(h, m, s, ##__VA_ARGS__)
 extern void iavf_debug_d(void *hw, u32 mask, char *fmt_str, ...)
-	__attribute__ ((format(gnu_printf, 3, 4)));
+	__printf(3, 4);
 
 typedef enum iavf_status_code iavf_status;
 #endif /* _IAVF_OSDEP_H_ */