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From: Arnd Bergmann <arnd@arndb.de>
To: "H.J. Lu" <hjl.tools@gmail.com>
Subject: Re: RFD: x32 ABI system call numbers
Date: Mon, 5 Sep 2011 19:21:59 +0200
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On Monday 05 September 2011, H.J. Lu wrote:
> I added MSG_CMSG_COMPAT64 and new compat system calls with
> 64bit timespec/val to support it.  See the enclosed patch.

Yes, looks good. Maybe there should be an #ifdef in there though,
so the other compat architectures don't get the extra code.

> BTW, I also added
> 
> compat_sys_preadv64(unsigned long fd, const struct compat_iovec __user *vec,
>          unsigned long vlen, loff_t pos)
> compat_sys_pwritev64(unsigned long fd, const struct compat_iovec __user *vec,
>          unsigned long vlen, loff_t pos)
> 
> to support 32bit compat_iovec * and 64bit offset.

Does that make much of a difference? I would guess that it's just as
easy to do in libc by splitting the pos argument and calling the
existing compat_sys_preadv. Alternatively, you could make glibc
copy the iovec array to the 64 bit format and call the native syscall,
because compat_rw_copy_check_uvector() otherwise just ends up doing that
in kernel space. Or you just define the x32 libc iovec to 

struct iovec {
	void *iov_base;
	unsigned int __pad; /* gets cleared by libc */
	__u64 iov_len;
}

	Arnd