linux-kernel - Re: [PATCH] tools/nolibc: align signature of ioctl() with POSIX

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Message-ID: <20250123131625.GD8580@1wt.eu>
Date: Thu, 23 Jan 2025 14:16:25 +0100
From: Willy Tarreau <w@....eu>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools/nolibc: align signature of ioctl() with POSIX

Hi Thomas,

On Thu, Jan 23, 2025 at 02:04:29PM +0100, Thomas Weißschuh wrote:
> POSIX defines the signature of ioctl() as follows,
> to allow passing a pointer or integer without casting:
> 	int ioctl(int fildes, int request, ... /* arg */);
> 
> Nolibc ioctl() expects a pointer, forcing the user to manually cast.
> Using va_arg to make the signature more flexible would work but seems to
> prevent inlining of the function. Instead use a macro. "fd" and "req"
> will still be typechecked through sys_ioctl().
> 
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  tools/include/nolibc/sys.h | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> index d4a5c2399a66b200ebf7ab249569cce2285481a5..5cb2c66cc8cccc4d4a1126acfd0b30a6efc886c3 100644
> --- a/tools/include/nolibc/sys.h
> +++ b/tools/include/nolibc/sys.h
> @@ -532,7 +532,7 @@ uid_t getuid(void)
>  
>  
>  /*
> - * int ioctl(int fd, unsigned long req, void *value);
> + * int ioctl(int fd, unsigned long req, ... value);
>   */
>  
>  static __attribute__((unused))
> @@ -541,11 +541,7 @@ int sys_ioctl(int fd, unsigned long req, void *value)
>  	return my_syscall3(__NR_ioctl, fd, req, value);
>  }
>  
> -static __attribute__((unused))
> -int ioctl(int fd, unsigned long req, void *value)
> -{
> -	return __sysret(sys_ioctl(fd, req, value));
> -}
> +#define ioctl(fd, req, value) __sysret(sys_ioctl(fd, req, (void *)(value)))

You risk to get a warning about casting a pointer from an integer of
a different size if you pass an int there. I think should should perform
a double cast instead:

  #define ioctl(fd, req, value) __sysret(sys_ioctl(fd, req, (void *)(uintptr_t)(value)))

That way any int should cast fine, and pointers should as well.

Willy