Re: [Qemu-devel] [PATCH] fcntl64 fix

[Stuart Anderson <anderson@netsweng.com>]

On Tue, 20 Mar 2007, Paul Brook wrote:

>> Now that the dust has settled, I see where the change is probably a
>> no-op anyway. A quick little test program indicates that on x86_64,
>> l_start will have an offset of 8 wether the structure is packed or not,
>> and wether the __pad member is present or not. The unsigned long long is
>> always going to be aligned to a 8 byte boundary.
>
> The __pad member is essential. Your logic is wrong is two ways:
>
> a) The struct is packed. This overrides normal alignment and ensures the
> structure contains no padding.

And in this case, it does remove some tail padding at the end of the
structure.

> b) long long has whatever alignment the host feels like giving it. There's no
> guarantee it's going to be 8 byte aligned.

No there isn't. This was just an observation of what occurs when
building a simple test case on x86_64.


                                  Stuart

Stuart R. Anderson                               anderson@netsweng.com
Network & Software Engineering                   http://www.netsweng.com/
1024D/37A79149:                                  0791 D3B8 9A4C 2CDC A31F
                                                   BD03 0A62 E534 37A7 9149