linux-kernel - Re: [PATCH v2] powerpc/setup_64: fix -Wempty-body warnings

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Message-ID: <55dc85b3e405821baafe9d8868ef921f99b6d103.camel@perches.com>
Date:   Thu, 27 Jun 2019 13:08:19 -0700
From:   Joe Perches <joe@...ches.com>
To:     Qian Cai <cai@....pw>, mpe@...erman.id.au
Cc:     paulus@...ba.org, benh@...nel.crashing.org,
        tyreld@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/setup_64: fix -Wempty-body warnings

On Thu, 2019-06-27 at 15:52 -0400, Qian Cai wrote:
> On Wed, 2019-06-05 at 16:53 -0400, Qian Cai wrote:
> > At the beginning of setup_64.c, it has,
> > 
> >   #ifdef DEBUG
> >   #define DBG(fmt...) udbg_printf(fmt)
> >   #else
> >   #define DBG(fmt...)
> >   #endif
> > 
> > where DBG() could be compiled away, and generate warnings,
> > 
> > arch/powerpc/kernel/setup_64.c: In function 'initialize_cache_info':
> > arch/powerpc/kernel/setup_64.c:579:49: warning: suggest braces around
> > empty body in an 'if' statement [-Wempty-body]
> >     DBG("Argh, can't find dcache properties !\n");
> >                                                  ^
> > arch/powerpc/kernel/setup_64.c:582:49: warning: suggest braces around
> > empty body in an 'if' statement [-Wempty-body]
> >     DBG("Argh, can't find icache properties !\n");
[]
> > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
[]
> > @@ -71,7 +71,7 @@
> >  #ifdef DEBUG
> >  #define DBG(fmt...) udbg_printf(fmt)
> >  #else
> > -#define DBG(fmt...)
> > +#define DBG(fmt...) do { } while (0)

I suggest

#define DBG(fmt...) do { if (0) udbg_printf(fmt); } while (0)

so that format and argument are always verified by the compiler.

I would also prefer a more generic form using ##__VA_ARGS__

#ifdef DEBUG
#define DBG(fmt, ...) udbg_printf(fmt, ##__VA_ARGS__)
#else
#define DBG(fmt, ...) do { if (0) udbg_printf(fmt, ##__VA_ARGS__); } while (0)
#endif

or maybe use the no_printk macro like

#ifdef DEBUG
#define DBG(fmt, ...) udbg_printf(fmt, ##__VA_ARGS__)
#else
#define DBG(fmt, ...) no_printk(fmt, ##__VA_ARGS__)
#endif