linux-kernel - Re: [RFC] clang: 'unused-function' warning on static inline functions

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Date:   Tue, 6 Jun 2017 17:28:40 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Steven Rostedt <rostedt@...dmis.org>,
        David Rientjes <rientjes@...gle.com>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Mark Brown <broonie@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [RFC] clang: 'unused-function' warning on static inline functions

El Tue, Jun 06, 2017 at 02:28:03PM -0700 Linus Torvalds ha dit:

> I applied the patch from David Rientjes to just make "inline"
> automatically mean "maybe unused" for clang.

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.