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From: David Leimbach <leimy2k@gmail.com>
Subject: Re: [9fans] 8c question
Date: Tue,  5 Jul 2005 08:35:01 -0700
To: Latchesar Ionkov <lucho@gmx.net>
Cc: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
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On Jul 5, 2005, at 8:27 AM, Latchesar Ionkov wrote:

> An example:
>
>     typedef struct {
>         ....
>         arch_vcpu_info_t arch;
>     } vcpu_info_t;
>
> For x86_32 and x86_64 arch_vcpu_info_t is defined as:
>
>     typedef struct {
>     } arch_vcpu_info_t;
>

That's undefined behavior by the C99 standard, as far as I can tell.

You are supposed to have a non-empty list of identifiers and types
in any given struct or union.

Definitely not good for portability.

Dave


>     Lucho
>
> On Mon, Jul 04, 2005 at 07:36:58PM -0700, David Leimbach said:
>
>> On 7/2/05, Charles Forsyth <forsyth@terzarima.net> wrote:
>>
>>>>> it cant be worked around without breaking the cross
>>>>> platform features of their headers.
>>>>>
>>>
>>> sounds brilliantly portable to me.
>>> what do they do?  insert 0-length padding areas
>>> to make these structures `portable'?
>>>
>>>
>>>
>> Yeah, it's undefined what happens if a struct is empty in C99.  
>> Seems a
>> really silly thing for someone to rely on.  What are they trying to
>> accomplish?  The only thing I can think of is some kind of type  
>> safety
>> based on a tag generated for a unique "struct".  They should probably
>> make it wrap a void * or something.
>