PR 18167, Relax PR 15228 protected visibility restriction

[Pedro Alves]

On 03/27/2015 04:54 PM, H.J. Lu wrote:
> On Fri, Mar 27, 2015 at 9:43 AM, Pedro Alves <palves@redhat.com> wrote:
>> On 03/27/2015 04:40 PM, H.J. Lu wrote:
>>> On Fri, Mar 27, 2015 at 9:38 AM, Pedro Alves <palves@redhat.com> wrote:
>>
>>>> Urgh.  The glibc issue sounds the most alarming.  If we can't keep
>>>> back compatibility, isn't there a new bit/attribute we can put
>>>> somewhere to tag new binaries with protected symbols in a
>>>> way that existing systems just error out when loading them?
>>>
>>>
>>> There is no backward compatibility to speak with since protected
>>> data symbol never worked before.
>>
>> OK, but when it's all fixed, programs and libraries will start
>> using the feature.  It'd be best if such programs/libraries just
>> failed to load in older systems, than crash or corrupt data at random.
>>
> 
> If one of gcc, glibc or binutils isn't fixed, the program may misbehave.
> I don't know how it be avoided at run-time with fixing all 3.

I'm not really worried about gcc or binutils.  Those are easy to
update.  The issue is picking a binary that was built against fixed
gcc and binutils, and then running it on an system that happens to
not have glibc fixed.  That just seems like ABI breakage.

How about emitting a reference to a symbol that only fixed glibc
provides?

Thanks,
Pedro Alves