Re: ARM compiler misbehaves ?

[Grant Edwards <grante at visi dot com>]

On Thu, Apr 29, 2004 at 04:48:27PM +0100, Richard Earnshaw wrote:

> There seems to be some general confusion here.  The thing I
> was (trying) to say doesn't work is placing the address of a
> packed object into a pointer to an object of the same base
> type.

Right.  We all knew that.  Nobody said it did.

What I said worked was referencing the field directly:

>>>test_struct.test_short = 0x1234;
>>>printf("%04x\n", test_struct.test_short);
>>>
>>>_may_ work.  I don't think it's guaranteed to work, though.   
>

And then Bill said it was actually guaranteed to work, and
after I looked up a few things, I agreed:

>> Actually, I'm pretty sure it is guaranteed to work as long as
>> the compiler can see the "packed" attribute during compilation
>
>I believe you're right.  It's only when you use the "&"  
>operator to hide the actual structure from the compiler that
>things go wrong.

And then you stated not only isn't it guaranteed to work, it
doesn't:

> None of them.  I was referring to the statement:
> 
>> Actually, I'm pretty sure it is guaranteed to work as long as
>> the compiler can see the "packed" attribute during compilation
>> (if it couldn't, that would be a serious structural problem in
>> your source code!).
> 
> Which claimed it should work.  It doesn't, and isn't intended
> to.

The statement with which you are disagreeing was that
referencing the fields directly (not through a pointer) is
guaranteed to work.

-- 
Grant Edwards
grante@visi.com

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