[PATCH] D30458: [ELF] - Make Bss and BssRelRo sections to be synthetic by nature.

[Rafael Avila de Espindola via llvm-commits]

>    // Dynamic section must be the last one in this list and dynamic
>    // symbol table section (DynSymTab) must be the first one.
>    finalizeSynthetic<ELFT>(
> -      {In<ELFT>::DynSymTab, In<ELFT>::GnuHashTab, In<ELFT>::HashTab,
> -       In<ELFT>::SymTab,    In<ELFT>::ShStrTab,   In<ELFT>::StrTab,
> -       In<ELFT>::VerDef,    In<ELFT>::DynStrTab,  In<ELFT>::GdbIndex,
> -       In<ELFT>::Got,       In<ELFT>::MipsGot,    In<ELFT>::IgotPlt,
> -       In<ELFT>::GotPlt,    In<ELFT>::RelaDyn,    In<ELFT>::RelaIplt,
> -       In<ELFT>::RelaPlt,   In<ELFT>::Plt,        In<ELFT>::Iplt,
> -       In<ELFT>::Plt,       In<ELFT>::EhFrameHdr, In<ELFT>::VerSym,
> -       In<ELFT>::VerNeed,   In<ELFT>::Dynamic});
> +      {In<ELFT>::Bss,        In<ELFT>::BssRelRo, In<ELFT>::DynSymTab,
> +       In<ELFT>::GnuHashTab, In<ELFT>::HashTab,  In<ELFT>::SymTab,
> +       In<ELFT>::ShStrTab,   In<ELFT>::StrTab,   In<ELFT>::VerDef,
> +       In<ELFT>::DynStrTab,  In<ELFT>::GdbIndex, In<ELFT>::Got,
> +       In<ELFT>::MipsGot,    In<ELFT>::IgotPlt,  In<ELFT>::GotPlt,
> +       In<ELFT>::RelaDyn,    In<ELFT>::RelaIplt, In<ELFT>::RelaPlt,
> +       In<ELFT>::Plt,        In<ELFT>::Iplt,     In<ELFT>::Plt,
> +       In<ELFT>::EhFrameHdr, In<ELFT>::VerSym,   In<ELFT>::VerNeed,
> +       In<ELFT>::Dynamic});

The comment is now out of date.

> Index: ELF/Relocations.cpp
> ===================================================================
> --- ELF/Relocations.cpp
> +++ ELF/Relocations.cpp
> @@ -479,8 +479,8 @@
>    // See if this symbol is in a read-only segment. If so, preserve the symbol's
>    // memory protection by reserving space in the .bss.rel.ro section.
>    bool IsReadOnly = isReadOnly<ELFT>(SS);
> -  OutputSection *OSec = IsReadOnly ? Out::BssRelRo : Out::Bss;
> -
> +  OutputSection *OSec =
> +      IsReadOnly ? In<ELFT>::BssRelRo->OutSec : In<ELFT>::Bss->OutSec;

This is a bit odd. We create the In<ELFT>::BssRelRo and In<ELFT>::Bss,
but they never hold anything. They are just a placeholder for output
sections.

I guess that instead of CopyRelSection it could be another
SyntheticSection type that is explicitly just a placeholder for an
output section.

Not sure if that is worth it, but it should at least have a comment if
we are to use CopyRelSection. Rui, what do you think?

Cheers,
Rafael