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

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Date:   Mon, 28 Feb 2022 12:02:38 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Guo Ren' <guoren@...nel.org>
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>,
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        "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

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.

	David

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