Darren Rook wrote:
> On Fri, Jan 16, 2009 at 10:59 AM, Ian Lance Taylor <iant@xxxxxxxxxx> wrote:
>
>>> Then why is attribute((packed)) provided? I really don't see a use
>>> for it. Why not rename it to __attribute__((addressviolation))?
>> The potential address violation only occurs when you take the address
>> of a field and pass it to another function. There are many ways to
>> use structures without taking the address of a field.
>
> So my example
>
> handle(&t.field2);
>
> has the potential to create an address violation, but these
> assignments do not(?):
>
> t.field2 = <some value>
> t->field2 = <some value>
That's right. The important thing to realize is that the type of &field2
in
struct test
{
UINT8 field1;
UINT16 field2;
UINT8 field3;
} __attribute__((__packed__));
is not UINT16 *; the compiler knows that it's an element of a packed
struct, and generates code accordingly. The correct procedure is always
to pass the address of the whole struct.
Andrew.
