[PATCH] D65995: [ELF] Don't special case symbolic relocations with 0 addend to ifunc in writable locations

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D65995#1622445 <https://reviews.llvm.org/D65995#1622445>, @ruiu wrote:

> > Currently the following 3 relocation types do not trigger the creation of a canonical PLT:
> > 
> > - GOT-generating
> > - PLT-generating
> > - symbolic relocation with 0 addend in a writable location
>
> Is it a typo that a PLT-generating relocation do *not* trigger the creation a canonical PLT, or am I missing something?


It isn't a typo. The creation of a canonical PLT refers to this piece of code:

  } else if (!needsPlt(expr)) {
    // Make the ifunc's PLT entry canonical by changing the value of its
    // symbol to redirect all references to point to it.
    unsigned entryOffset = sym.pltIndex * target->pltEntrySize;
    if (config->zRetpolineplt)
      entryOffset += target->pltHeaderSize;
  
    auto &d = cast<Defined>(sym);
    d.section = in.iplt;
    d.value = entryOffset;
    d.size = 0;
    // It's important to set the symbol type here so that dynamic loaders
    // don't try to call the PLT as if it were an ifunc resolver.
    d.type = STT_FUNC;

It changes the type from STT_GNU_IFUNC to STT_FUNC.

If a non-preemptable ifunc just has PLT-generating and GOT-generating relocations. The type doesn't need a change.


Repository:
  rLLD LLVM Linker

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D65995/new/

https://reviews.llvm.org/D65995