On Fri, Nov 7, 2008 at 10:52 PM, Marcus Tangermann
<Marcus.Tangermann@xxxxxx> wrote:
> Hi,
>
> we use an XScale 422 (ARM) with a big endian Linux system based on the buildroot environment. It seems there is an alignment problem we have. I've tracked down the problem to the following.
> 1. The data received via a netlink communication from the kernel is stored into a buffer buf. The data is correct.
> 2. The address of the buffer is converted to a pointer to nlmsghdr:
> struct nlmsghdr *h;
> h = (struct nlmsghdr*) buf;
> printf("IPSECTOOLS: Length %04d\n", h->nlmsg_len);
> printf("IPSECTOOLS: Type %02d\n", h->nlmsg_type);
> The results of printf are nonsens. The first fields seem to have an offset of 2 bytes, at the end there also seem to be swapped bytes.
> 3. To test what might happen, I've created an own struct
> struct aligntest{
> __u32 first;
> __u32 int second;
> __u32 third;
> __u32 fourth;
> };
> When you now set a point to a buffer, again the values are wrong:
> s1 = (struct aligntest*) buf;
> printf("1: %08X\n", s1->first);
> printf("2: %08X\n", s1->second);
> printf("3: %08X\n", s1->third);
> printf("4: %08X\n", s1->fourth);
>
> It seems, that there is a problem with the unsigned int values. When you add the attribute "packed" to the definition of struct aligntest ( __attribute__(__packed__) ), all values are displayed correctly.
> So, any hints what the problem can be?
I'm not sure what the problem is? You can't generally misalign a
struct pointer safely.
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