linux-kernel - Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

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Message-Id: <20160204105931.7422c17d0bd1b92a387d97c9@linux-foundation.org>
Date:	Thu, 4 Feb 2016 10:59:31 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Andrzej Hajda <a.hajda@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	open list <linux-kernel@...r.kernel.org>,
	Bob Peterson <rpeterso@...hat.com>
Subject: Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more
 types

On Thu, 04 Feb 2016 13:40:38 +0100 Arnd Bergmann <arnd@...db.de> wrote:

> diff --git a/include/linux/err.h b/include/linux/err.h
> index b7d4a9ff6342..bd4936a2c352 100644
> --- a/include/linux/err.h
> +++ b/include/linux/err.h
> @@ -18,9 +18,7 @@
>  
>  #ifndef __ASSEMBLY__
>  
> -#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \
> -				? unlikely((x) <= -1) \
> -				: unlikely((x) >= (typeof(x))-MAX_ERRNO))
> +#define IS_ERR_VALUE(x)	(unlikely((unsigned long long)(x) >= (unsigned long long)(typeof(x))-MAX_ERRNO))
>  
>  static inline void * __must_check ERR_PTR(long error)
>  {
> 
> 
> I'm not sure if the cast to 'unsigned long long' might cause less
> efficient code to be generated by gcc. I would hope that it is smart
> enough to not actually extend shorter variables to 64 bit before
> doing the comparison but I have not checked yet.

I did a quick test with i386 on drivers/nvmem/core.o.  The patch takes
the text size from 9098 bytes to 9133.  That file has 11 instances of
IS_ERR_VALUE().