linux-kernel - Re: [PATCH v2 2/4] linux/const.h: move UL() macro to include/linux/const.h

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Date:   Fri, 06 Jan 2017 10:45:55 +0000
From:   David Howells <dhowells@...hat.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     dhowells@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Olof Johansson <olof@...om.net>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Alexander Popov <alex.popov@...ux.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        James Morse <james.morse@....com>,
        linux-kernel@...r.kernel.org,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Laura Abbott <labbott@...hat.com>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Pratyush Anand <panand@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH v2 2/4] linux/const.h: move UL() macro to include/linux/const.h

Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> diff --git a/include/uapi/linux/const.h b/include/uapi/linux/const.h
> index c872bfd..76fb0f9 100644
> --- a/include/uapi/linux/const.h
> +++ b/include/uapi/linux/const.h
> @@ -1,7 +1,7 @@
>  /* const.h: Macros for dealing with constants.  */
>  
> -#ifndef _LINUX_CONST_H
> -#define _LINUX_CONST_H
> +#ifndef _UAPI_LINUX_CONST_H
> +#define _UAPI_LINUX_CONST_H

You need to be very careful doing this.  Some userspace stuff depends on the
guard macro names on the kernel header files.

>  /* Some constant macros are used in both assembler and
>   * C code.  Therefore we cannot annotate them always with
> @@ -21,7 +21,10 @@
>  #define _AT(T,X)	((T)(X))
>  #endif
>  
> +#define _UL(x)		(_AC(x, UL))
> +#define _ULL(x)		(_AC(x, ULL))

How likely is this to collide with existing userspace code somewhere?  It
looks like the sort of thing that could collide with a C library.

David