linux-kernel - Re: [PATCH 2/3] doc,vdso: Make vDSO examples more portable

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Message-ID: <539A071B.2080101@zytor.com>
Date:	Thu, 12 Jun 2014 13:01:31 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Kui Zhang <kuizhang@...il.com>
CC:	x86@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefani Seibold <stefani@...bold.net>
Subject: Re: [PATCH 2/3] doc,vdso: Make vDSO examples more portable

On 06/12/2014 11:47 AM, Andy Lutomirski wrote:
>  
> +#include <asm/bitsperlong.h>
> +

This isn't portable in any way.  This is probably not the right way to
do this.

The portable way to do this would be something like:

#include <limits.h>

#if ULONG_MAX > 0xffffffffUL
# define ELF_BITS 64
#else
# define ELF_BITS 32
#endif

There is also the option of looking for either __LP64__ or __ILP32__
which isn't 100% portable but works with all newer versions of gcc:

#ifndef ELF_BITS
# ifdef __LP64__
#  define ELF_BITS 64
# elif defined(__ILP32__)
#  define ELF_BITS 32
# else
#  error "Unknown size, please define ELF_BITS"
# endif
#endif

... or something like that.

	-hpa

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