Re: [lwip-users] [PATCH] fix warning for gcc and possible unaligned access

[Timmy Brolin]

Personally I had problems with Texas Instruments compiler and DSPs.
Unfortunately I worked with the Texas compiler at the local university, 
and I do not have access to the university any more.

There was a big discussion in the mailing list about alignment issues 
back then. I was not the only one who had alignment problems.
I suggest taking a look in the mailing list archive..

Regards,
Timmy Brolin

Curt McDowell wrote:

> More observations about structure packing:
>
> In gcc, it seems the __attribute__((packed)) is inherited by all
> sub-structures.  But in armcc, the compiler disallows normal structures from
> being members of __packed structures.  So simply making 'struct ipaddr'
> unpacked isn't going to work for all compilers.  Maybe there should be a packed
> and unpacked version of struct ipaddr, so that the compiler doesn't have to
> generate unaligned support code everywhere struct ipaddr is used.
>
> I think Pedro is right and just about any compiler that supports packed
> structures must support assigning, referencing or copying unaligned uint32
> members.  ip_addr2 first came into use in etharp.c:1.55 on 04/27/04 to fix bug
> #8708.  Leon or Timmy, do you happen to remember which was the offending
> compiler that couldn't generate the right code for this case?  Or was the code
> really doing something illegal like *(uint32 *)&ipaddr?
>
> Regards,
> Curt McDowell
> Broadcom Corp.
>
>
>
>
>
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