Re: [lwip-users] Misalignment problems on PowerPC (little endian mode)

[address@hidden]

Hi Ikhwan,

Sorry I didn't answer for so long but I was out of town for quite a while.
I'm glad to hear you solved the problem. Still I cannot understand why 
your compiler (or rather its vendor) doesn't support structure packing 
which is a rather common element of C (even if it is not included in the 
C-standard, or is it?)

> I have solved this problem by copying the ip tcp and all the necessary 
> headers into a separate variable which will be processed during packet 
> reception. This has removed all my alignment problems.
While this works for you, it is really a workaround:
a) While structure packing is, of course, slower than accessing aligned 
data, copying is even slower!
b) You will have to work around this for every new part of the stack as 
well as every existing part (I don't know if receiving TCP/IP packets is 
the only problem: I imagine sending them wouldn't work as well?)
c) And this is the most critical to me: You will have the same problem 
with many third-party ethernet/network/socket software such as 
server/client implementations (ftp/http/tftp...) or event industrial 
ethernet stacks running on your target (if any).
> I have the source which can be compiled if the option 
> LWIP_MISALIGNMENT is set to 1. If anyone interested and have the same 
> problem, I am more than willing to share and help. If you guys want to 
> incorporate it to lwip as alternative solution to structure packing I 
> am glad I can help. This lowers the stack performance a bit though.

Not to offend you, but personally, I see this as a bug in the compiler 
you are using and we don't support broken compilers: structure packing 
_is_ a must for lwIP!

Hope you are still having fun with lwIP!

Simon