[PATCH] D73139: [LLD][COFF] Enable linking of __declspec(selectany) symbols from Clang and GCC

[Markus Böck via Phabricator via llvm-commits]

zero9178 created this revision.
zero9178 added reviewers: ruiu, pcc.
Herald added subscribers: llvm-commits, mstorsjo.
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zero9178 edited the summary of this revision.
zero9178 edited the summary of this revision.
zero9178 edited the summary of this revision.

When annotating a symbol with declspec(selectany), Clang assigns it comdat 2 while GCC assigns it comdat 3. This patch enables two object files that contain a declspec(selectany) symbol, one created by gcc and the other by clang, to be linked together instead of issuing a duplicate symbol error.

Would need someone to commit this for me if accepted.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D73139

Files:
  lld/COFF/InputFiles.cpp


Index: lld/COFF/InputFiles.cpp
===================================================================
--- lld/COFF/InputFiles.cpp
+++ lld/COFF/InputFiles.cpp
@@ -500,6 +500,17 @@
     leaderSelection = selection = IMAGE_COMDAT_SELECT_LARGEST;
   }
 
+  // GCCs __declspec(selectany) doesn't actually pick "any" but "same size as".
+  // Clang on the other hand picks "any". To be able to link two object files
+  // with a __declspec(selectany) declaration, one compiled with gcc and the other
+  // with clang, we merge them as proper "any"
+  if (config->mingw && ((selection == IMAGE_COMDAT_SELECT_ANY &&
+                         leaderSelection == IMAGE_COMDAT_SELECT_SAME_SIZE) ||
+                        (selection == IMAGE_COMDAT_SELECT_SAME_SIZE &&
+                         leaderSelection == IMAGE_COMDAT_SELECT_ANY))) {
+    leaderSelection = selection = IMAGE_COMDAT_SELECT_ANY;
+  }
+
   // Other than that, comdat selections must match.  This is a bit more
   // strict than link.exe which allows merging "any" and "largest" if "any"
   // is the first symbol the linker sees, and it allows merging "largest"


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