Re: [PATCH 2/3] Revert "[AArch64][BZ #17711] Fix extern protected data handling"

["maskray@google.com" <maskray@google.com>]

On 2022-05-24, Wilco Dijkstra wrote:
>Hi,

Hi Wilco,

>>> * Clang code generation treats STV_PROTECTED the same way as STV_HIDDEN:
>>>   no GOT-generating relocation in the first place.
>
>We should change GCC's behaviour to match this - is this something that
>applies to all targets?

I have a blog post on the topic about copy relocations and protected
symbols:
https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected

"The GCC pessimization applies to all ports with #define TARGET_BINDS_LOCAL_P default_binds_local_p_2."

The aarch64 pessimization was due to the side affect of a commit
attempting to fix another issue: commit
cbddf64c0243816b45e6680754a251c603245dbc (From-SVN: r222992)

>>> * gold and lld reject copy relocation on a STV_PROTECTED symbol.
>>> * Nowadays -fpie/-fpic modes are popular. GCC/Clang's codegen uses
>>>   GOT-generating relocation when accessing an default visibility
>>>   external symbol which avoids copy relocation.
>
>Would it be reasonable to add a way to override settings for binaries?
>For example if all imported symbols are marked with the correct visibility,
>PIE binaries could avoid using GOT for default visibility external symbols to
>get better performance. And non-PIE binaries could force GOT accesses for
>non-default visibility to avoid copy relocations and support protected visibility.

In Clang, -fno-direct-access-external-data is such an option:)

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Regarding function symbols, there is a bit which should be fixed:
"Protected function symbols and canonical PLT entries"