Re: [PATCH 1/4] makedumpfile: redefine numerical limitaction macros.

[Petr Tesarik <ptesarik@suse.cz>]

On Sat, 26 Apr 2014 12:07:06 +0800
Wang Nan <wangnan0@huawei.com> wrote:

> From: Wang Nan <pi3orama@gmail.com>
> 
> According to C standard, numerical limitations macros such as ULONG_MAX
> should be defined in <limits.h>, and must be defined as "constant
> expressions suitable for use in #if preprocessing directives." (see
> "Numerical limits" section in the standard).
> 
> Original definition in common.h breaks this rule:
> 
>  #define LONG_MAX ((long)(~0UL>>1))
> 
> which causes macros like following failure:
> 
>  #if LONG_MAX == 2147483647
>  # define LONG_BIT	32
>  #else
>  # define LONG_BIT	64
>  #endif
> 
> Unfortunately, the above code piece is taken from real glibc header
> (/usr/include/bits/xopen_lim.h), which is happen to be included by
> <limits.h> if _GNU_SOURCE is defined.
> 
> This patch include <limits.h> in common.h to use C standard numerical
> macros. For system without such macros defined by C, this patch also
> defines L(L)ONG_MAX in a standard compatible way. By checking wich
> 
> gcc -dM -E - <<<''
> 
> we know that __LONG_MAX__ and __LLONG_MAX__ macros should be defined by
> gcc by default. Definition of ULONG_MAX and ULLONG_MAX are taken from
> gcc standard include file (include-fixed/limits.h).
> 
> In addition, macro ULONGLONG_MAX is nonstandard, the standard way for
> defining max ulonglong is ULLONG_MAX.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
> Cc: Petr Tesarik <ptesarik@suse.cz>
> Cc: kexec@lists.infradead.org
> Cc: Geng Hui <hui.geng@huawei.com>
> Cc: Liu Hua <sdu.liu@huawei.com>
> 
> ---
>  common.h | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/common.h b/common.h
> index 6ad3ca7..124f107 100644
> --- a/common.h
> +++ b/common.h
> @@ -16,17 +16,29 @@
>  #ifndef _COMMON_H
>  #define _COMMON_H
>  
> +#include <limits.h>
> +
>  #define TRUE		(1)
>  #define FALSE		(0)
>  #define ERROR		(-1)
>  
>  #ifndef LONG_MAX
> -#define LONG_MAX	((long)(~0UL>>1))
> +# warning LONG_MAX should have been defined in <limits.h>
> +# define LONG_MAX	__LONG_MAX__
>  #endif
>  #ifndef ULONG_MAX
> -#define ULONG_MAX	(~0UL)
> +# warning ULONG_MAX should have been defined in <limits.h>
> +# define ULONG_MAX	(LONG_MAX * 2UL + 1UL)
> +#endif
> +#ifndef LLONG_MAX
> +# warning LLONG_MAX should have been defined in <limits.h>
> +# define LLONG_MAX __LONG_LONG_MAX__
> +#endif
> +#ifndef ULLONG_MAX
> +# warning ULLONG_MAX should have been defined in <limits.h>
> +# define ULLONG_MAX (LLONG_MAX * 2ULL + 1ULL)
>  #endif
> -#define ULONGLONG_MAX	(~0ULL)
> +#define ULONGLONG_MAX	ULLONG_MAX

Hi Wang Nan,

is this actually needed on some known platform? If not, then I'd rather
remove all these #ifndef stanzas and rely on <limits.h>. I mean, if you
can't rely on standard C constants, then why should be the gcc-specific
pre-defined macros (__LONG_MAX__ et al.) available?

It's probably better to put the burden on the person doing the
port, because they should know what is appropriate for their compiler
and/or libc.

Just my opinion,
Petr T

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