linux-kernel - Re: [PATCH 4/5] drivers: staging: erofs: Fix parentheses error in macro

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Date:   Tue, 11 Dec 2018 07:48:58 -0800
From:   Joe Perches <joe@...ches.com>
To:     Gao Xiang <gaoxiang25@...wei.com>,
        Aaron Strahlberger <aaron.strahlberger@...teo.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chao Yu <yuchao0@...wei.com>, linux-erofs@...ts.ozlabs.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        linux-kernel@...cs.fau.de,
        Julius Wiedmann <julius.wiedmann@....de>,
        Dominik Huber <domi250@....de>
Subject: Re: [PATCH 4/5] drivers: staging: erofs: Fix parentheses error in
 macro

On Tue, 2018-12-11 at 19:06 +0800, Gao Xiang wrote:
> Hi Aaron,
> 
> On 2018/12/11 18:54, Aaron Strahlberger wrote:
> > Fix of ERROR: Macros with complex values should be enclosed in parentheses
> > from checkpatch.pl
[]
> > diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
[]
> > @@ -38,9 +38,9 @@ struct erofs_super_block {
> >  /* 80 */__u8 reserved2[48];     /* 128 bytes */
> >  } __packed;
> >  
> > -#define __EROFS_BIT(_prefix, _cur, _pre)	enum {	\
> > +#define __EROFS_BIT(_prefix, _cur, _pre)	(enum { \
> >  	_prefix ## _cur ## _BIT = _prefix ## _pre ## _BIT + \
> > -		_prefix ## _pre ## _BITS }
> > +	_prefix ## _pre ## _BITS })
> 
> It seems not the valid C, here is the compiler error:
> 
> ...
> 
> In file included from drivers/staging/erofs/internal.h:25:0,
>                  from drivers/staging/erofs/xattr.h:16,
>                  from drivers/staging/erofs/xattr.c:14:
> drivers/staging/erofs/erofs_fs.h:41:43: error: expected identifier or ‘(’ before ‘enum’
>  #define __EROFS_BIT(_prefix, _cur, _pre) (enum { \
>                                            ^
> drivers/staging/erofs/erofs_fs.h:65:1: note: in expansion of macro ‘__EROFS_BIT’
>  __EROFS_BIT(EROFS_I_, DATA_MAPPING, VERSION);
>  ^~~~~~~~~~~
> make[3]: *** [scripts/Makefile.build:292: drivers/staging/erofs/xattr.o] Error 1
> 
> ...
> 
> 
> the __EROFS_BIT marco is used to define yyy_BIT according to xxx_BIT + xxx_BITS for cascade, eg.
> 
> __EROFS_BIT(EROFS_I_, DATA_MAPPING, VERSION);
> it will defines EROFS_I_DATA_MAPPING_BIT = EROFS_I_VERSION_BIT + EROFS_I_VERSION_BITS;
> 
> __EROFS_BIT(EROFS_I_, FEATURE2, DATA_MAPPING);
> it will defines EROFS_I_FEATURE2_BIT = EROFS_I_DATA_MAPPING_BIT + EROFS_I_DATA_MAPPING_BITS;

This macro is used only once and is merely obfuscation
for that one use.  Please remove the macro and expand
it in the one place it is used.