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

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

[Masahiro Yamada]

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))
 
 /* generic data direction definitions */
 #define READ			0
-- 
2.7.4

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

[H. Peter Anvin]

[-- Attachment #1: Type: text/plain, Size: 1256 bytes --]

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 --]
[-- Type: text/plain, Size: 1602 bytes --]

/*
 * 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; })))))

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

[Masahiro Yamada]

Hi.

2017-03-30 6:24 GMT+09:00 H. Peter Anvin <hpa@zytor.com>:
> 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


Could you care to send a patch?

Perhaps, ALIGN and PTR_ALIGN can be merged as well?



-- 
Best Regards
Masahiro Yamada

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

[H. Peter Anvin]

On 03/29/17 18:57, Masahiro Yamada wrote:
> 
> Could you care to send a patch?
> 
> Perhaps, ALIGN and PTR_ALIGN can be merged as well?
> 

Can't promise when I'd get around to it...

	-hpa

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

[Masahiro Yamada]

Hi.

2017-03-30 12:29 GMT+09:00 H. Peter Anvin <hpa@zytor.com>:
> On 03/29/17 18:57, Masahiro Yamada wrote:
>>
>> Could you care to send a patch?
>>
>> Perhaps, ALIGN and PTR_ALIGN can be merged as well?
>>
>
> Can't promise when I'd get around to it...
>
>         -hpa

OK. No need to rush now.
Please take a look when you find some time.


Andrew,
Maybe, we should drop my patch for now,
and take our time for better implementation?





-- 
Best Regards
Masahiro Yamada

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

[Andrew Morton]

On Wed, 29 Mar 2017 19:22:10 +0900 Masahiro Yamada <yamada.masahiro@socionext.com> 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.
> 
> ...
>
> --- 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))
>  
>  /* generic data direction definitions */
>  #define READ			0

It would be nice to see some conversions which actually use this new
macro.