linux-kernel - Re: [PATCH 10/27] drivers/infiniband/core: Use memdup

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Message-ID: <adaaars0xy1.fsf@roland-alpha.cisco.com>
Date:	Sat, 22 May 2010 08:15:50 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	wharms@....de
Cc:	Julia Lawall <julia@...u.dk>, Roland Dreier <rolandd@...co.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 10/27] drivers/infiniband/core: Use memdup_user

 > > +	data = memdup_user((void __user *)(unsigned long)src, len);
 > > +	if (IS_ERR(data))
 > > +		return PTR_ERR(data);

 > This cast look strange, can it happen that (unsigned long)<(u64) ?
 > (is there a 32bit infiniband) ?

There is 32-bit infiniband.  Linux kernel assumes that unsigned long is
equivalent to uintptr_t -- in other words all pointers are the same size
as longs.  So when casting from integer to pointer we add a cast to
unsigned long to avoid a warning precisely in the 32-bit case -- we
would get a warning about cast to pointer from integer of different size
when casting from 64-bit integer to 32-bit pointer.
-- 
Roland Dreier <rolandd@...co.com> || For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/index.html
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