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Re: Preventing preemption of 'protected' symbols in GNU ld 2.26

On Tue, Mar 29, 2016 at 12:54 PM, H.J. Lu <> wrote:
> On Tue, Mar 29, 2016 at 12:51 PM, Joe Groff <> wrote:
>>> On Mar 29, 2016, at 12:43 PM, H.J. Lu <> wrote:
>>> The link-time shared library may be very different from the run-time
>>> shared library.  Since copy relocation works correctly against protected
>>> symbol with the current gcc, binutils and glibc, we can't simply disallow
>>> copy relocation against protected symbol at link-time.
>> However, protected doesn't work this way in older binutils, or with alternative tools like llvm or gold, and it sounds like protected was never intended to work this way either. Rather If gcc is interested in pursuing this optimization, it seems more responsible to me they could investigate introducing language-level annotations that let libraries opt into the optimization, instead of unilaterally breaking things for other binutils clients and introducing new complexity to get back to the original behavior.
> Protected symbol never worked correctly on x86 before.  My
> change closed a few long-standing bugs.  There is no going-back.

If you want to avoid copy relocation, you can do

1. Pass -z noextern-protected-data to build the shared object.
2. Use GOT to access external data in executable.


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