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Date:   Wed, 23 Sep 2020 15:25:49 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 5/9] fs: remove various compat readv/writev helpers
Message-ID: <20200923142549.GK3421308@ZenIV.linux.org.uk>
References: <20200923060547.16903-1-hch@lst.de>
 <20200923060547.16903-6-hch@lst.de>
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On Wed, Sep 23, 2020 at 08:05:43AM +0200, Christoph Hellwig wrote:
>  COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
> -		const struct compat_iovec __user *,vec,
> +		const struct iovec __user *, vec,

Um...  Will it even compile?

>  #ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
>  COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
> -		const struct compat_iovec __user *,vec,
> +		const struct iovec __user *, vec,

Ditto.  Look into include/linux/compat.h and you'll see

asmlinkage long compat_sys_preadv64(unsigned long fd,
                const struct compat_iovec __user *vec,
                unsigned long vlen, loff_t pos);

How does that manage to avoid the compiler screaming bloody
murder?