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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] dummy field in CPUTLBEntry?
Date: Mon, 19 Apr 2010 23:43:26 +0100
References: <s2sfdaac4d51004160200ybd50cef7u949ab1625f889ac8@mail.gmail.com>
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To: qemu-devel@nongnu.org
Cc: Jun Koi <junkoi2004@gmail.com>

> I find the way we calculate the dummy field in CPUTLBEntry funny. What
> is the point of having:
> 
>                    ((-sizeof(target_ulong) * 3) & (sizeof(unsigned long) -
>  1))
> 
> in its size? Why shouldnt it be more simple, like below?
> 
>     uint8_t dummy[(1 << CPU_TLB_ENTRY_BITS) - (sizeof(target_ulong) *
> 3 + sizeof(unsigned long))];
> 

No, because of alignment.
Consider the case of 32-bit target_ulong and 64-bit unsigned long).

Paul