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

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Date:   Thu, 02 Dec 2021 19:10:52 -0500
From:   "Zack Weinberg" <zack@...folio.org>
To:     "Adhemerval Zanella" <adhemerval.zanella@...aro.org>,
        "Rich Felker" <dalias@...c.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 Thu, Dec 2, 2021, at 6:43 PM, Adhemerval Zanella via Libc-alpha wrote:
> 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.

As a general rule yes, but we could make a deal that some specific bits headers are permanent API for use by things like this. They probably should be less of a dumping ground than bits/types.h though.