Re: [PATCH] kernel.h: add IS_PTR_ALIGNED() macro

["H. Peter Anvin" <hpa@zytor.com>]

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On 03/29/17 03:22, Masahiro Yamada wrote:
> We often check if a pointer has a specific alignment.  Because the
> '&' (bitwise AND) operator cannot take a pointer for the operand,
> so we need a cast like, IS_ALIGNED((unsigned long)p, a).
> 
> IS_PTR_ALIGNED will be useful as a shorthand.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
>  include/linux/kernel.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index e5edd55..a810e4b 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -50,6 +50,7 @@
>  #define __ALIGN_MASK(x, mask)	__ALIGN_KERNEL_MASK((x), (mask))
>  #define PTR_ALIGN(p, a)		((typeof(p))ALIGN((unsigned long)(p), (a)))
>  #define IS_ALIGNED(x, a)		(((x) & ((typeof(x))(a) - 1)) == 0)
> +#define IS_PTR_ALIGNED(p, a)		(IS_ALIGNED((unsigned long)p, a))
>  

No need for two macros; make one work for both.

You could move the __inttype() macro from arch/x86/include/asm/uaccess.h
into this file and replace typeof(x) with __inttype(x) in the above macro.

Attached is a set of slightly improved (safer and a bit more
generalized) versions of the same macro that might be more appropriate
to include in <linux/kernel.h>.

	-hpa

[-- Attachment #2: uinttype.c --]
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/*
 * These are types: corresponding to the smallest unsigned/signed
 * integer type no smaller than int or long, respectively, capable of
 * holding the argument (which can be anything that can be validly
 * passed to sizeof().)
 *
 * If the size is too large even for a long long, they return an
 * unnamed structure type with the right sizeof(), which if used for a
 * cast will generate the error message:
 *
 * error: conversion to non-scalar type requested
 */
#define __uinttype(x)							\
  __typeof__(__builtin_choose_expr(sizeof(x) <= sizeof(0U), 0U,		\
             __builtin_choose_expr(sizeof(x) <= sizeof(0UL), 0UL,	\
	     __builtin_choose_expr(sizeof(x) <= sizeof(0ULL), 0ULL,	\
	     ({ struct { unsigned char __bad[sizeof(x)]; } __bad = {{0}}; \
	        __bad; })))))
#define __sinttype(x)							\
  __typeof__(__builtin_choose_expr(sizeof(x) <= sizeof(0), 0,		\
             __builtin_choose_expr(sizeof(x) <= sizeof(0L), 0L,		\
	     __builtin_choose_expr(sizeof(x) <= sizeof(0LL), 0LL,	\
	     ({ struct { signed char __bad[sizeof(x)]; } __bad = {{0}}; \
	        __bad; })))))
#define __ulongtype(x)							\
  __typeof__(__builtin_choose_expr(sizeof(x) <= sizeof(0UL), 0UL,	\
	     __builtin_choose_expr(sizeof(x) <= sizeof(0ULL), 0ULL,	\
	     ({ struct { unsigned char __bad[sizeof(x)]; } __bad = {{0}}; \
	        __bad; }))))
#define __slongtype(x)							\
  __typeof__(__builtin_choose_expr(sizeof(x) <= sizeof(0L), 0L,		\
	     __builtin_choose_expr(sizeof(x) <= sizeof(0LL), 0LL,	\
	     ({ struct { signed char __bad[sizeof(x)]; } __bad = {{0}}; \
	        __bad; })))))