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

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Message-ID: <20211202153422.GH7074@brightrain.aerifal.cx>
Date:   Thu, 2 Dec 2021 10:34:23 -0500
From:   Rich Felker <dalias@...c.org>
To:     Zack Weinberg <zack@...folio.org>
Cc:     Cyril Hrubis <chrubis@...e.cz>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        libc-alpha@...rceware.org, ltp@...ts.linux.it
Subject: Re: [PATCH] uapi: Make __{u,s}64 match {u,}int64_t in userspace

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.

Rich