[PATCH] D91583: [LTO] Prevent devirtualization for symbols exported to dynamic linker

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


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Comment at: lld/ELF/LTO.cpp:252
+    r.VisibleToDynamicLinker =
+        sym->isExportDynamic(sym->kind(), sym->visibility) ||
+        sym->inDynamicList;
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tejohnson wrote:
> MaskRay wrote:
> > `sym->exportDynamic || sym->inDynamicList`
> > 
> > Then `isExportDynamic` does not need to be public.
> sym->exportDynamic is false for linkonce_odr vtables, that was what I was referencing in this comment (otherwise I could use includeInDynsym which checks that):
> 
> > Note that I couldn't use includeInDynsym in lld because that is not set for linkonce_odr symbols that were thus have canBeOmittedFromSymbolTable set (since any referencing module must have it's own copy) - we still want to block the LTO visibility upgrade for those symbols to avoid WPD. So I am using a slightly different interface that more directly checks whether export-dynamic is in effect.
Sorry, I don't understand the difference. If I replace this with `sym->exportDynamic`, I don't get a test failure...


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Comment at: llvm/include/llvm/LTO/LTO.h:466
+  /// by a shared library not visible to the linker.
+  unsigned VisibleToDynamicLinker : 1;
+
----------------
MaskRay wrote:
> tejohnson wrote:
> > MaskRay wrote:
> > > How about VisibleToOtherModules?
> > > 
> > > The name VisibleToDynamicLinker is too tied to the ELF binary format.
> > VisibleToOtherModules sounds to me like it means LLVM Modules that are being linked together statically. I wanted to note that these are symbols that may have dynamic references not seen by the static link. Is there anything like --export-dynamic for other binary formats? If not, then it is ELF specific anyway.
> @rnk for thoughts on COFF.
Perhaps another name is `Exported`.

For ELF, the does not seem to be restricted to shared objects seen as in the input file.


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  https://reviews.llvm.org/D91583/new/

https://reviews.llvm.org/D91583