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Date: Fri, 23 May 2014 13:35:45 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/4] buildsys: Fix module build for
	block-iscsi.so
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To: Michael Tokarev <mjt@tls.msk.ru>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>, Stefan Weil <sw@weilnetz.de>, Michael Roth <mdroth@linux.vnet.ibm.com>, Christophe Fergeau <cfergeau@redhat.com>, Alon Levy <alevy@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, =?ISO-8859-1?Q?Alex_Benn=E9e?= <alex.bennee@linaro.org>, Richard Henderson <rth@twiddle.net>

Il 23/05/2014 11:59, Michael Tokarev ha scritto:
> 23.05.2014 07:02, Fam Zheng wrote:
>> We get:
>>
>>     $ qemu-img
>>     Failed to open module: /home/fam/build/master/block-iscsi.so: undefined symbol: bitmap_set
>>     qemu-img: Not enough arguments
>>     Try 'qemu-img --help' for more information
>>
>> Because since commit b03c38 (block/iscsi: speed up read for unallocated
>> sectors), block/iscsi.c calls utils/bitmap.c:bitmap_* functions, which is not
>> linked to qemu-img nor shared objects.
>
> Heh. This is a very fun situation.
>
> For the first time I've had it with postfix in about 2002,
> when I tried to make postfix modular, and it didn't work,
> because modules sometimes used symbols which are not present
> in all executables who used the modules.
>
> The solution is not link modules with missing symbols.  The
> solution is to make libpostfix.so with all ths support functions,
> and link all programs to it instead of using all support funcs
> statically.

Another solution is to turn libqemuutil.a into a libtool convenience 
library, which is a portable way to wrap it with 
--whole-archive/--no-whole-archive.  This will make libtool mandatory 
for compilation of QEMU.

Paolo