problem with -mstructure-size-boundary=8 and network stack

[JIANGJason]

HI all,
I am working on a porting of RTEMS 4.10.2(tried 4.9.4 also) to a S3C2440/CS8900 based SBC, and with problem to let the network stack to work.

(1) If  -mstructure-size-boundary=8 is used, data abort will be occur at ip_input.c:400 (the problem code is listed below) when there is a IP packet incoming, such as ICMP, or any other. The 

ip_input.c:400
if (IA_SIN(ia)->sin_addr.s_addr == ip->ip_dst.s_addr) goto ours;

(1) If  -mstructure-size-boundary=32 is used, any IP packet out send is in abnormal format. and wireshark told me that the packet it captured are all "Bogus IP header length (0, must be at least 20)".

I am not familiar with the IP stack itself, but it looks can not be easily solved by just change the compiling options. Anyone had the same problem before? 
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Best Regards, Jason