Using __attribute((packed))__ on picky architectures

[Andrew Haley]

Darren Rook wrote:
> On Fri, Jan 16, 2009 at 10:59 AM, Ian Lance Taylor <iant@google.com> 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.