Re: [PATCH] Don't check ABI for _nl_default_dirname

[David Miller <davem at davemloft dot net>]

From: Andi Kleen <ak@linux.intel.com>
Date: Sun, 9 Dec 2012 21:20:35 -0800

> On Sun, Dec 09, 2012 at 06:28:42PM -0800, Jonathan Nieder wrote:
>> Andreas Schwab wrote:
>> 
>> > The size is copied into the program by the COPY relocation.
>> 
>> Yep, that's why I didn't write a patch after reporting PR14664.
>> 
>> Are applications that use _nl_default_dirname buggy by definition
>> because its size can vary from machine to machine?  I'm inclined to
> 
> They are only buggy if they rely on a particular size or content
> (or rather length, as in strlen, as they cannot even know the true
> size)

But, as already mentioned, the size is encoded into the COPY reloc.

So the dynamic linker "notices" that your application linked with
a "different" instance of the symbol, since the size is different,
and it will signal an error.

This happens in the handling of R_*_COPY in every target's
dl-machine.h file.

It's therefore complete and utter garbage to just let this ABI check
pass as the symbol's size is encoded into, and checked, in every
application that references the symbol.