Date: Tue, 6 Jun 2017 22:59:50 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Matthias Kaehlcke <mka@chromium.org>
cc: Arnd Bergmann <arnd@arndb.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Steven Rostedt <rostedt@goodmis.org>,
        Douglas Anderson <dianders@chromium.org>,
        Guenter Roeck <linux@roeck-us.net>, Mark Brown <broonie@kernel.org>,
        David Miller <davem@davemloft.net>
Subject: Re: [RFC] clang: 'unused-function' warning on static inline
 functions
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On Tue, 6 Jun 2017, Matthias Kaehlcke wrote:

> Unfortunately as is the patch doesn't work:
> 
> include/linux/compiler-clang.h:20:9: error: 'inline' macro redefined [-Werror,-Wmacro-redefined]
> #define inline inline __attribute__((unused))
>         ^
> include/linux/compiler-gcc.h:78:9: note: previous definition is here
> #define inline          inline          notrace
> 
> Another version of David's patch (https://lkml.org/lkml/2017/5/24/878)
> first undefines 'inline' before redefining it:
> 
> #ifdef inline
> #undef inline
> #define inline inline __attribute__((unused))
> #endif
> 
> This works at least in the sense of not causing compiler errors. I
> couldn't validate if it actually still indicates the compiler to
> inline a function, since in any case 'inline' is only a
> recommendation. In the few experiments I did without the patch clang
> didn't make a difference between static inline and non-inline
> functions.
> 
> The redefinition above could be used to fix the build error, however
> it would imply to lose the extra attributes from compiler-gcc.h.
> 

I've followed up with a patch that handles this behavior in compiler-gcc.h 
since clang defines __GNUC__ as well, so clang gets both compiler-gcc.h 
and compiler-clang.h behavior.

I've tested it, but please feel free to add your Tested-by for more 
confidence in the change.

Linus, who currently maintains include/linux/compiler*.h changes?  I see 
only an entry for a sparse maintainer.  I'd happily manage a cross 
compiler setup if it would be helpful to prevent this type of issue in the 
future.  First question would be if there is a minimum gcc major version 
intended to be supported?