linux-kernel - Re: [PATCH] uapi: Make __{u,s}64 match {u,}int64

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Date:   Thu, 2 Dec 2021 20:43:19 -0300
From:   Adhemerval Zanella <adhemerval.zanella@...aro.org>
To:     Rich Felker <dalias@...c.org>, Zack Weinberg <zack@...folio.org>
Cc:     linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        libc-alpha@...rceware.org, linux-kernel@...r.kernel.org,
        ltp@...ts.linux.it
Subject: Re: [PATCH] uapi: Make __{u,s}64 match {u,}int64_t in userspace



On 02/12/2021 20:29, Rich Felker wrote:
> On Thu, Dec 02, 2021 at 10:34:23AM -0500, Rich Felker wrote:
>> On Mon, Nov 22, 2021 at 10:19:59PM +0000, Zack Weinberg via Libc-alpha wrote:
>>> On Mon, Nov 22, 2021, at 4:43 PM, Cyril Hrubis wrote:
>>>> This changes the __u64 and __s64 in userspace on 64bit platforms from
>>>> long long (unsigned) int to just long (unsigned) int in order to match
>>>> the uint64_t and int64_t size in userspace.
>>> ....
>>>> +
>>>> +#include <asm/bitsperlong.h>
>>>> +
>>>>  /*
>>>> - * int-ll64 is used everywhere now.
>>>> + * int-ll64 is used everywhere in kernel now.
>>>>   */
>>>> -#include <asm-generic/int-ll64.h>
>>>> +#if __BITS_PER_LONG == 64 && !defined(__KERNEL__)
>>>> +# include <asm-generic/int-l64.h>
>>>> +#else
>>>> +# include <asm-generic/int-ll64.h>
>>>> +#endif
>>>
>>> I am all for matching __uN / __sN to uintN_t / intN_t in userspace, but may I suggest the technically simpler and guaranteed-to-be-accurate
>>>
>>>  /*
>>> - * int-ll64 is used everywhere now.
>>> + * int-ll64 is used everywhere in kernel now.
>>> + * In user space match <stdint.h>.
>>>   */
>>> +#ifdef __KERNEL__
>>>  # include <asm-generic/int-ll64.h>
>>> +#elif __has_include (<bits/types.h>)
>>> +# include <bits/types.h>
>>> +typedef __int8_t __s8;
>>> +typedef __uint8_t __u8;
>>> +typedef __int16_t __s16;
>>> +typedef __uint16_t __u16;
>>> +typedef __int32_t __s32;
>>> +typedef __uint32_t __u32;
>>> +typedef __int64_t __s64;
>>> +typedef __uint64_t __u64;
>>> +#else
>>> +# include <stdint.h>
>>> +typedef int8_t __s8;
>>> +typedef uint8_t __u8;
>>> +typedef int16_t __s16;
>>> +typedef uint16_t __u16;
>>> +typedef int32_t __s32;
>>> +typedef uint32_t __u32;
>>> +typedef int64_t __s64;
>>> +typedef uint64_t __u64;
>>> +#endif
>>>
>>> The middle clause could be dropped if we are okay with all uapi
>>> headers potentially exposing the non-implementation-namespace names
>>> defined by <stdint.h>. I do not know what the musl libc equivalent
>>> of <bits/types.h> is.
>>
>> We (musl) don't have an equivalent header or __-prefixed versions of
>> these types.
>>
>> FWIW I don't think stdint.h exposes anything that would be problematic
>> alongside arbitrary use of kernel headers.
> 
> Also, per glibc's bits/types.h:
> 
> /*
>  * Never include this file directly; use <sys/types.h> instead.
>  */
> 
> it's not permitted (not supported usage) to #include <bits/types.h>.
> So I think the above patch is wrong for glibc too. As I understand it,
> this is general policy for bits/* -- they're only intended to work as
> included by the libc system headers, not directly by something else.

You are right, the idea is to allow glibc to create and remove internal headers.