linux-kernel - Re: + uapi-fix-linux-sysctlh-userspace-compilation-errors.patch added to -mm tree

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Date:   Mon, 27 Feb 2017 12:38:16 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: + uapi-fix-linux-sysctlh-userspace-compilation-errors.patch added
 to -mm tree

On Sat, Feb 25, 2017 at 1:35 AM, Dmitry V. Levin <ldv@...linux.org> wrote:
> On Fri, Feb 24, 2017 at 05:35:33PM +0300, Alexey Dobriyan wrote:
>> On Thu, Feb 23, 2017 at 02:44:31PM -0800, akpm@...ux-foundation.org wrote:
>> > /usr/include/linux/sysctl.h:38:2: error: unknown type name 'size_t'
>> >   size_t *oldlenp;
>> > /usr/include/linux/sysctl.h:40:2: error: unknown type name 'size_t'
>> >   size_t newlen;
>>
>> > --- a/include/uapi/linux/sysctl.h~uapi-fix-linux-sysctlh-userspace-compilation-errors
>> > +++ a/include/uapi/linux/sysctl.h
>> > @@ -26,6 +26,10 @@
>> >  #include <linux/types.h>
>> >  #include <linux/compiler.h>
>> >
>> > +#ifndef __KERNEL__
>> > +#include <stddef.h>                /* For size_t. */
>> > +#endif
>>
>> There is __kernel_size_t for cases like this.
>
> No, __kernel_size_t is not for cases like this because size_t differs
> from __kernel_size_t on x32 and mips n32.
>
> Fortunately, there is no sysctl syscall entry on x32, but on mips m32
> it is there with number 6152, implemented using compat_sys_sysctl.
> The latter operates with argument of type struct compat_sysctl_args*
> where newlen is of type compat_size_t.
>
> If you change it from size_t to __kernel_size_t, you'll break mips n32.

You're gluing kernel interface to an userspace header
which kernel doesn't control. How can this fix anything?