linux-kernel - Re: [PATCH v3] uapi: Make __{u,s}64 match {u,}int64

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Date:   Tue, 21 Jun 2022 15:01:24 +0200
From:   Alejandro Colomar <alx.manpages@...il.com>
To:     Cyril Hrubis <chrubis@...e.cz>, linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, libc-alpha@...rceware.org,
        linux-api@...r.kernel.org, dhowells@...hat.com,
        David.Laight@...lab.com, zack@...folio.org, ltp@...ts.linux.it,
        linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH v3] uapi: Make __{u,s}64 match {u,}int64_t in userspace

On 6/21/22 14:03, 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 for C code.
> 
> We cannot make the change for C++ since that would be non-backwards
> compatible change and may cause possible regressions and even
> compilation failures, e.g. overloaded function may no longer find a
> correct match.
> 
> This allows us to use the kernel structure definitions in userspace in C
> code. For example we can use PRIu64 and PRId64 modifiers in printf() to
> print structure membere. Morever with this there would be no need to
> redefine these structures in an libc implementations as it is done now.
> 
> Consider for example the newly added statx() syscall. If we use the
> header from uapi we will get warnings when attempting to print it's
> members as:
> 
> 	printf("%" PRIu64 "\n", stx.stx_size);
> 
> We get:
> 
> 	warning: format '%lu' expects argument of type 'long unsigned int',
> 	         but argument 5 has type '__u64' {aka 'long long unsigned int'}
> 
> Signed-off-by: Cyril Hrubis <chrubis@...e.cz>

Acked-by: Alejandro Colomar <alx.manpages@...il.com>

> ---
>   include/uapi/asm-generic/types.h | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> v2: Make sure we do not break C++ applications
> v3: Update commit message to explain C++ exclusion
> 
> diff --git a/include/uapi/asm-generic/types.h b/include/uapi/asm-generic/types.h
> index dfaa50d99d8f..11e468a39d1e 100644