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Re: [Xen-devel] xen build error on gcc v4.5.0

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] xen build error on gcc v4.5.0
From: M A Young <m.a.young@xxxxxxxxxxxx>
Date: Wed, 18 Aug 2010 20:44:38 +0100 (BST)
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Masroor Vettuparambil <Masroor.Vettuparambil@xxxxxxxx>
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On Wed, 18 Aug 2010, Jeremy Fitzhardinge wrote:

On 08/18/2010 03:24 AM, Masroor Vettuparambil wrote:
I got the below error when I do a 'make world' in xen-testing.hg . The kernel 
is gcc version is 4.5.0.
It is working with gcc v4.3.0
Btw  I thought the default kernel in xen-testing.hg is 2.6.32.x, but it is 
still 2.6.31.x.


  LD      drivers/xen/blktap/blktap.o
  LD      drivers/xen/blktap/built-in.o
  CC      drivers/xen/netback/netback.o
/home/xen/xen-4.0-testing.hg/linux-2.6-pvops.git/drivers/xen/netback/netback.c: In 
function ânet_rx_actionâ:
/home/xen/xen-4.0-testing.hg/linux-2.6-pvops.git/drivers/xen/netback/netback.c:495:32: error: 
storage size of ârx_mclâ isnât constant

Looks like a gcc bug.  Older gccs can compute __RING_SIZE() as a
compile-time constant, but gcc 4.5.0 apparently isn't doing that.  It
is, admittedly, a very complex expression, but gcc shouldn't regress
like this.  I'm not sure how to work around it.

One option is to use __CONST_RING_SIZE instead of __RING_SIZE if that is available. I had a similar problem compiling xen with gcc 4.5 where this worked.

        Michael Young
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