[cxx-abi-dev] Re: C++ ABI: Reuse of tail padding

[Kerch Holt]

Mark Mitchell wrote:
> 
> 
> --On Wednesday, August 14, 2002 10:15:07 PM +0100 Nathan Sidwell 
> <nathan at codesourcery.com> wrote:
> 
>> Mark Mitchell wrote:
>>
>>> We have a problem here.
>>
>>
>>> Intel's compiler does not pack things into the tail padding.
>>> Neither, I expect, does HP's.
>>
>> I would like to get hard data from more than the two compilers
>> you've verified.

Looks like the HP compiler does make use of the tail padding.
For example it reports "sizeof(S2)" to be 12. I think c2
is placed in the "tail padding".

So this would favor g++'s implementation.

Kerch

> 
> 
> There aren't many more to find.  HP, Intel, and GCC are the compilers
> that have implemented the ABI to date.
> 
> Others are in the process, which is part of why this is important.
> 
>>> I think I would prefer to change G++, and drop this idea from the spec,
>>> even though it is an optimization.
>>
>>
>> Although using tail padding is neat, how many bytes would it
>> save in real programs? You only get it with structs of the form
>>     int i;
>>     char c;
>> or (on some non-i86 machines)
>>     double d;
>>     int i;
> 
> 
> Exactly.
> 
> Well, that sounds like two votes for changing G++ (and clarifying the
> spec to drop any hint of using tail padding).
>