linux-kernel - Re: [PATCH v3 21/31] arm64: 32-bit (compat) applications support

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Date:	Thu, 13 Sep 2012 11:03:27 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 21/31] arm64: 32-bit (compat) applications support

On Thursday 13 September 2012, Catalin Marinas wrote:
> Here they are. For converting the other architectures, I'll post
> separate patches as I don't want to add an extra dependency to the
> arm64 series.

Ok, thanks!


> diff --git a/kernel/compat.c b/kernel/compat.c
> index c28a306..5f07388 100644
> --- a/kernel/compat.c
> +++ b/kernel/compat.c
> @@ -1215,6 +1215,50 @@ compat_sys_sysinfo(struct compat_sysinfo __user *info)
>         return 0;
>  }
>  
> +#ifdef __ARCH_WANT_COMPAT_SYS_SENDFILE
> +asmlinkage int compat_sys_sendfile(int out_fd, int in_fd,
> +                                  compat_off_t __user *offset, s32 count)
> +{
> +       mm_segment_t old_fs = get_fs();
> +       int ret;
> +       off_t of;
> +
> +       if (offset && get_user(of, offset))
> +               return -EFAULT;
> +
> +       set_fs(KERNEL_DS);
> +       ret = sys_sendfile(out_fd, in_fd,
> +                          offset ? (off_t __user *)&of : NULL, count);
> +       set_fs(old_fs);
> +
> +       if (offset && put_user(of, offset))
> +               return -EFAULT;
> +       return ret;
> +}
> +#endif /* __ARCH_WANT_COMPAT_SYS_SENDFILE */

Looking at this code in detail now, I think it's better to move the functions to
fs/read_write.c and get rid of the get_fs/set_fs hack, like

asmlinkage int compat_sys_sendfile(int out_fd, int in_fd,
                                   compat_off_t __user *offset, s32 count)
{       
        loff_t pos;
        compat_off_t off;
        ssize_t ret;
        
        if (offset) {
                if (unlikely(get_user(off, offset)))
                        return -EFAULT;
                pos = off;
                ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
                if (unlikely(put_user(pos, offset)))
                        return -EFAULT;
                return ret;
        }
        
        return do_sendfile(out_fd, in_fd, NULL, count, 0);
}

This implementation is smaller and more efficient than the common one.

Same for compat_sys_sendfile64, although I don't think there is ever
a case where loff_t is defined differently from compat_loff_t, so
you can probably just use the native sys_sendfile64 for the compat
case.

>  
> +#ifdef __ARCH_WANT_COMPAT_SYS_SCHED_RR_GET_INTERVAL
> +asmlinkage int compat_sys_sched_rr_get_interval(compat_pid_t pid,
> +                                               struct compat_timespec __user *interval)
> +{
> +       struct timespec t;
> +       int ret;
> +       mm_segment_t old_fs = get_fs();
> +
> +       set_fs(KERNEL_DS);
> +       ret = sys_sched_rr_get_interval(pid, (struct timespec __user *)&t);
> +       set_fs(old_fs);
> +       if (put_compat_timespec(&t, interval))
> +               return -EFAULT;
> +       return ret;
> +}
> +#endif /* __ARCH_WANT_COMPAT_SYS_SCHED_RR_GET_INTERVAL */
> +

This one looks reasonable. It would be nice to kill the get_fs/set_fs but here
it would just make the native code slower or duplicate a lot of it.

Acked-by: Arnd Bergmann <arnd@...db.de>
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