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From: Roland Dreier <rdreier@cisco.com>
To: Randy Dunlap <randy.dunlap@oracle.com>
Cc: linux-kernel@vger.kernel.org, Roland Dreier <rolandd@cisco.com>,
       akpm@linux-foundation.org
Subject: Re: mmotm 2009-08-04-14-22 uploaded (ummunotify)
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Date: Tue, 04 Aug 2009 17:38:29 -0700
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 > ummunotify.c:(.text+0x8f217): undefined reference to `__get_user_X'
 > 
 > when building for i386.
 > 
 > The get_user() and put_user() in ummunotify_exchange_features()
 > are correctly converted to __get_user_4() and __put_user_4(),
 > but the get_user() in ummunotify_unregister_region() becomes
 > __get_user_X()  [as seen in objdump output].

Is 64-bit get_user() supposed to work portably?  Because it seems that
arch/x86/include/asm/uaccess.h intentionally makes get_user((__u64))
expand to __get_user_X() and then never defines __get_user_X().  And
arm, say, expands it to __get_user_bad().  But on the other hand,
powerpc and sparc seem to go to the trouble of defining a 64-bit
get_user() for 32-bit builds...

My fault for insufficient 32-bit compile testing.  Andrew, I'll send a
patch to change to copy_from_user() instead.

 - R.