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

[Florian Weimer <fweimer@redhat.com>]

* Wilco Dijkstra:

> Hi Florian,
>
> Sure, something basic like this shows the issues:
>
> int x;
> int f(void) { return ++x; }
> int main(void) { return f(); }
>
> compile with -O2 -fPIC -flto -shared:
>
> 00000000000004f0 <f@plt>:
>  4f0:   b0000090        adrp    x16, 11000 <__cxa_finalize@GLIBC_2.17>
>  4f4:   f9400611        ldr     x17, [x16, #8]
>  4f8:   91002210        add     x16, x16, #0x8
>  4fc:   d61f0220        br      x17
>
> 0000000000000510 <main>:
>  510:   17fffff8        b       4f0 <f@plt>
>
> 0000000000000600 <f>:
>  600:   90000081        adrp    x1, 10000 <__FRAME_END__+0xf8f8>
>  604:   f947e821        ldr     x1, [x1, #4048]
>  608:   b9400020        ldr     w0, [x1]
>  60c:   11000400        add     w0, w0, #0x1
>  610:   b9000020        str     w0, [x1]
>  614:   d65f03c0        ret

Can you link with a version script?

{ local: *; global: main; };

Exporting symbols inhibits some optimizations even if interposition is
assumed not to happen because the behavior of public entry points needs
to be preserved.  With a version script, the set of entry points can be
greatly reduced, enabling further optimizations.

Thanks,
Florian