[PATCH] D154198: [JITLink][PowerPC] Add TOC and relocations for ppc64

[Kai Luo via Phabricator via llvm-commits]

lkail added inline comments.


================
Comment at: llvm/include/llvm/ExecutionEngine/JITLink/ppc64.h:112-117
+    case RequestToBeGOTEntry: {
+      this->appendEntry(
+          E.getTarget(),
+          G.addAnonymousSymbol(*B, 0, G.getPointerSize(), false, false));
+      E.setKind(ppc64::Pointer64);
+      return true;
----------------
lhames wrote:
> Just to make sure I follow:
> 
> `ELFLinkGraphBuilder_ppc64` converts `R_PPC64_ADDR64` to `RequestToBeGOTEntry` when it's a relocation _from_ a preexisting GOT entry in the object file?
> 
> Rather than using a special edge kind, could we walk the `.toc` section in the `buildTables_ELF_ppc64` function to pre-register the entries before calling `visitExistingEdges`?  Would that allow us to drop the `RequestToBeGOTEntry` edge kind and use `Pointer64` unconditionally for `R_PPC64_ADDR64`?
> 
> I'm imagining something like:
> 
> ```
> template <support::endianness Endianness>
> Error buildTables_ELF_ppc64(LinkGraph &G) {
>   LLVM_DEBUG(dbgs() << "Visiting edges in graph:\n");
>   ppc64::TOCTableManager<Endianness> TOC;
> 
>   // Register preexisting GOT entries with TOC table manager.
>   if (auto *dotTOCSection = G.findSectionByName(".toc")) {
>     for (<each GOT entry>)
>       TOC.appendEntry(<entry target>, <entry symbol>);
>   }
> 
>   ppc64::PLTTableManager<Endianness> PLT(TOC);
>   createELFGOTHeader(G, TOC);
>   visitExistingEdges(G, TOC, PLT);
>   ...
> ```
> ELFLinkGraphBuilder_ppc64 converts R_PPC64_ADDR64 to RequestToBeGOTEntry when it's a relocation _from_ a preexisting GOT entry in the object file?

Yes, that's the case.

> Rather than using a special edge kind, could we walk the .toc section in the buildTables_ELF_ppc64 function to pre-register the entries before calling visitExistingEdges?

That sounds nice.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D154198/new/

https://reviews.llvm.org/D154198