linux-kernel - Re: [PATCH V7 03/20] compat: consolidate the compat

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Date:   Mon, 28 Feb 2022 20:13:22 +0800
From:   Guo Ren <guoren@...nel.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     "palmer@...belt.com" <palmer@...belt.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "anup@...infault.org" <anup@...infault.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "liush@...winnertech.com" <liush@...winnertech.com>,
        "wefu@...hat.com" <wefu@...hat.com>,
        "drew@...gleboard.org" <drew@...gleboard.org>,
        "wangjunqiang@...as.ac.cn" <wangjunqiang@...as.ac.cn>,
        "hch@....de" <hch@....de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH V7 03/20] compat: consolidate the compat_flock{,64} definition

On Mon, Feb 28, 2022 at 8:02 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Guo Ren
> > Sent: 28 February 2022 11:52
> >
> > On Mon, Feb 28, 2022 at 2:40 PM David Laight <David.Laight@...lab.com> wrote:
> > >
> > > From: guoren@...nel.org
> > > > Sent: 27 February 2022 16:28
> > > >
> > > > From: Christoph Hellwig <hch@....de>
> > > >
> > > > Provide a single common definition for the compat_flock and
> > > > compat_flock64 structures using the same tricks as for the native
> > > > variants.  Another extra define is added for the packing required on
> > > > x86.
> > > ...
> > > > diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
> > > ...
> > > >  /*
> > > > - * IA32 uses 4 byte alignment for 64 bit quantities,
> > > > - * so we need to pack this structure.
> > > > + * IA32 uses 4 byte alignment for 64 bit quantities, so we need to pack the
> > > > + * compat flock64 structure.
> > > >   */
> > > ...
> > > > +#define __ARCH_NEED_COMPAT_FLOCK64_PACKED
> > > >
> > > >  struct compat_statfs {
> > > >       int             f_type;
> > > > diff --git a/include/linux/compat.h b/include/linux/compat.h
> > > > index 1c758b0e0359..a0481fe6c5d5 100644
> > > > --- a/include/linux/compat.h
> > > > +++ b/include/linux/compat.h
> > > > @@ -258,6 +258,37 @@ struct compat_rlimit {
> > > >       compat_ulong_t  rlim_max;
> > > >  };
> > > >
> > > > +#ifdef __ARCH_NEED_COMPAT_FLOCK64_PACKED
> > > > +#define __ARCH_COMPAT_FLOCK64_PACK   __attribute__((packed))
> > > > +#else
> > > > +#define __ARCH_COMPAT_FLOCK64_PACK
> > > > +#endif
> > > ...
> > > > +struct compat_flock64 {
> > > > +     short           l_type;
> > > > +     short           l_whence;
> > > > +     compat_loff_t   l_start;
> > > > +     compat_loff_t   l_len;
> > > > +     compat_pid_t    l_pid;
> > > > +#ifdef __ARCH_COMPAT_FLOCK64_PAD
> > > > +     __ARCH_COMPAT_FLOCK64_PAD
> > > > +#endif
> > > > +} __ARCH_COMPAT_FLOCK64_PACK;
> > > > +
> > >
> > > Provided compat_loff_t are correctly defined with __aligned__(4)
> > See include/asm-generic/compat.h
> >
> > typedef s64 compat_loff_t;
> >
> > Only:
> > #ifdef CONFIG_COMPAT_FOR_U64_ALIGNMENT
> > typedef s64 __attribute__((aligned(4))) compat_s64;
> >
> > So how do you think compat_loff_t could be defined with __aligned__(4)?
>
> compat_loff_t should be compat_s64 not s64.
>
> The same should be done for all 64bit 'compat' types.
Changing
typedef s64 compat_loff_t;
to
typedef compat_s64 compat_loff_t;

should be another patch and it affects all architectures, I don't
think we should involve it in this series.

look at kernel/power/user.c:
struct compat_resume_swap_area {
        compat_loff_t offset;
        u32 dev;
} __packed;

I thnk keep "typedef s64 compat_loff_t;" is a sensible choice for
COMPAT support patchset series.

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/