[Bug ld/26815] Unnecessary error on linking STV_PROTECTED library: relocation R_X86_64_PC32 against protected symbol `f' can not be used when making a shared object

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26815

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Thiago Macieira from comment #4)
> (In reply to H.J. Lu from comment #3)
> > GOT relocation is needed for function pointer comparison.
> > 
> > > Either way, the fact that gold and ld.bfd behave different is a problem. 
> > > And
> > > so is the fact that passing an empty --dynamic-list file causes it to 
> > > work.
> > 
> > An empty --dynamic-list file is the same as -Bsymbolic.
> 
> I see.
> 
> Then this is an incompatibility between compiler and linker: the compiler
> sees a protected symbol and emits a relocation assuming it doesn't need
> indirect access via the GOT to do a pointer comparison, but ld.bfd says it
> should.
> 
> Anyway, this is what I am asking to change: when a symbol is protected, the
> compiler optimisation should be allowed and pointer comparison still works
> provided ALL users use the GOT too. That includes the executable.

This is an ABI change.  We have 2 choices

1. Extend GNU_PROPERTY_NO_COPY_ON_PROTECTED to cover protected function
pointers.  We can rename it to GNU_PROPERTY_LOCAL_PROTECTED,  Or
2. Add a new property for protected function pointers.

Please raise the issue at

https://gitlab.com/x86-psABIs/Linux-ABI

This will require support in GCC, linker and ld.so.

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