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

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Message-Id: <c5993ee9-1b5d-4469-9c0e-8d4e0fbd575a@www.fastmail.com>
Date:   Mon, 22 Nov 2021 22:19:59 +0000
From:   "Zack Weinberg" <zack@...folio.org>
To:     "Cyril Hrubis" <chrubis@...e.cz>, linux-kernel@...r.kernel.org
Cc:     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 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.

zw