[cxx-abi-dev] Deleted virtual functions

[Mark Mitchell]

Lawrence Crowl wrote:

>> I do not think it would be a good idea to require that a compiler
>> put __cxa_pure_virtual into the virtual table.  For code-size
>> optimization, having a simple NULL pointer is better.
> 
> Why is this a concern?  The tables are in .rodata and bounded by
> the number of distinct classes, which is generally quite reasonable.

On small embedded systems, every byte counts.  Period.

For example, some of the new Luminary Micro ARM-based parts have 8K
flash.  And, yes, people want to use C++ on such systems.

> I am not convinced that a new compiler will be able to use an old
> library in general. 

It may not.  But, that's up to the compiler.  If the ABI mandates that
virtual table slots for deleted virtual functions *must* contain the
address of __cxa_deleted_virtual that prevents what might be a good
implementation choice on some systems.  For example, someone might want
to be able to use deleted virtual functions on an existing Linux
distribution, without having to upgrade libstdc++.

-- 
Mark Mitchell
CodeSourcery
mark at codesourcery.com
(650) 331-3385 x713