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Re: [Qemu-devel] [PATCH] fcntl64 fix

From: Stuart Anderson
Subject: Re: [Qemu-devel] [PATCH] fcntl64 fix
Date: Wed, 21 Mar 2007 09:50:43 -0400 (EDT)

On Tue, 20 Mar 2007, Paul Brook wrote:

Now that the dust has settled, I see where the change is probably a
no-op anyway. A quick little test program indicates that on x86_64,
l_start will have an offset of 8 wether the structure is packed or not,
and wether the __pad member is present or not. The unsigned long long is
always going to be aligned to a 8 byte boundary.

The __pad member is essential. Your logic is wrong is two ways:

a) The struct is packed. This overrides normal alignment and ensures the
structure contains no padding.

And in this case, it does remove some tail padding at the end of the

b) long long has whatever alignment the host feels like giving it. There's no
guarantee it's going to be 8 byte aligned.

No there isn't. This was just an observation of what occurs when
building a simple test case on x86_64.


Stuart R. Anderson                               address@hidden
Network & Software Engineering                   http://www.netsweng.com/
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