Re: [lwip-users] cast increases required alignment of target type

[Simon Goldschmidt]

Joe Dupre wrote:
> I've had this warning since v1.3.1.  How can I make it go away?
> [..]
>   opts = (u32_t *)(seg->tcphdr + 1);  <----WARNING: cast increases required
> alignment of target type
> [..]
> This is with arm-elf-gcc (yagarto build 20091018).
> If I understand it correctly, the warning is because seg->tcp_hdr is not
> falling on a 32 bit boundary.
> But I don't know how to correct this.

The problem is that lwIP does not only rely on the compiler's automatic 
alignment but takes care of alignment itself. In this case, the tcphdr will 
always be aligned because the pbuf's payload pointer is aligned. I just spotted 
that warning, too (interesingly, nios2-elf-gcc v3.4.1 only gives me this 
warning when compiling as C++, not when compiling as C).

However, I'm curious: this warning should be issued when compiling other files, 
too (e.g. sockets.c, mem.c, memp.c), didn't you get those warnings?

Up to now, I think we said "turn off the alignment warning" when compiling the 
lwIP code, but at least for gcc, it seems to be enough to add a cast to (void*) 
in between. Maybe I'll add that to the code... That way, we are safe to still 
get alignement warnings where we didn't explicitly disable them.

Simon
-- 
Sicherer, schneller und einfacher. Die aktuellen Internet-Browser -
jetzt kostenlos herunterladen! http://portal.gmx.net/de/go/atbrowser