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Date:	Thu, 20 Jul 2006 17:18:39 +0100
To:	hemanth.venkatesh@wipro.com
Cc:	linux-mips@linux-mips.org
Subject: Re: Bit operations work differently on MIPS and IA32
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From:	Thiemo Seufer <ths@networkno.de>
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hemanth.venkatesh@wipro.com wrote:
> Hi All,
> 
>  
> 
> I ran the below program on an IA32 and AU1100 machine, both being little
> endian machines and got different results. Does anyone know what could
> be the cause of this behaviour. This problem is blocking us from booting
> the cramfs rootfs.
> 
>  
> 
> #include <stdio.h>
> 
> typedef unsigned int u32;
> 
> main()
> 
> {
> 
> struct tmp{
> 
> u32 namelen:6,offset:26;
> 
> }tmp1;
> 
> (*(int *)(&tmp1))=0x4c0;

This makes non-portable assumptions about the bitfield layout. The
results are platform-dependent (or rather ABI-dependent). Portable
code needs to avoid acessing bitfields via typecasts.


Thiemo