[llvm-objcopy] Don't apply --localize flags to common symbols

Summary:
--localize-symbol and --localize-hidden will currently localize common symbols. GNU objcopy will not localize these symbols even when explicitly requested, which seems reasonable; common symbols should always be global so they can be merged during linking.

See PR39461

Reviewers: jakehehrlich, jhenderson, alexshap, MaskRay, espindola

Reviewed By: jakehehrlich, jhenderson, alexshap, MaskRay

Subscribers: emaste, arichardson, alexshap, MaskRay, llvm-commits

Differential Revision: https://reviews.llvm.org/D53782

llvm-svn: 345856

llvm/test/tools/llvm-objcopy/localize-hidden.test

@@ -55,6 +55,12 @@ Symbols:
       Value:    0x2006
       Size:     2
       Visibility: STV_HIDDEN
+    - Name:     hiddenGlobalCommon
+      Type:     STT_OBJECT
+      Index:    SHN_COMMON
+      Value:    0x2006
+      Size:     2
+      Visibility: STV_HIDDEN
     - Name:     undefGlobal
       Type:     STT_FUNC
       Size:     8
@@ -142,6 +148,17 @@ Symbols:
 #CHECK-NEXT:    Section: .text
 #CHECK-NEXT:  }
 #CHECK-NEXT:  Symbol {
+#CHECK-NEXT:    Name: hiddenGlobalCommon
+#CHECK-NEXT:    Value: 0x2006
+#CHECK-NEXT:    Size: 2
+#CHECK-NEXT:    Binding: Global
+#CHECK-NEXT:    Type: Object
+#CHECK-NEXT:    Other [
+#CHECK-NEXT:      STV_HIDDEN
+#CHECK-NEXT:    ]
+#CHECK-NEXT:    Section: Common (0xF
+#CHECK-NEXT:  }
+#CHECK-NEXT:  Symbol {
 #CHECK-NEXT:    Name: undefGlobal
 #CHECK-NEXT:    Value: 0x0
 #CHECK-NEXT:    Size: 8

llvm/test/tools/llvm-objcopy/localize.test

@@ -1,5 +1,10 @@
 # RUN: yaml2obj %s > %t
-# RUN: llvm-objcopy --localize-symbol Global -L Local -L Weak %t %t2
+# RUN: llvm-objcopy \
+# RUN:     --localize-symbol Global \
+# RUN:     -L Local \
+# RUN:     -L Weak \
+# RUN:     -L GlobalCommon \
+# RUN:     %t %t2
 # RUN: llvm-readobj -symbols %t2 | FileCheck %s
 
 !ELF
@@ -40,6 +45,11 @@ Symbols:
       Size:     8
       Section:  .text
       Value:    0x1010
+    - Name:     GlobalCommon
+      Type:     STT_OBJECT
+      Index:    SHN_COMMON
+      Value:    0x2006
+      Size:     2
 
 #CHECK: Symbols [
 #CHECK-NEXT:  Symbol {
@@ -78,4 +88,13 @@ Symbols:
 #CHECK-NEXT:    Other: 0
 #CHECK-NEXT:    Section: .text
 #CHECK-NEXT:  }
+#CHECK-NEXT:  Symbol {
+#CHECK-NEXT:    Name: GlobalCommon
+#CHECK-NEXT:    Value: 0x2006
+#CHECK-NEXT:    Size: 2
+#CHECK-NEXT:    Binding: Global
+#CHECK-NEXT:    Type: Object
+#CHECK-NEXT:    Other: 0
+#CHECK-NEXT:    Section: Common (0xF
+#CHECK-NEXT:  }
 #CHECK-NEXT:]

llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp

@@ -213,10 +213,11 @@ static void handleArgs(const CopyConfig &Config, Object &Obj,
   // them.
   if (Obj.SymbolTable) {
     Obj.SymbolTable->updateSymbols([&](Symbol &Sym) {
-      if ((Config.LocalizeHidden &&
-           (Sym.Visibility == STV_HIDDEN || Sym.Visibility == STV_INTERNAL)) ||
-          (!Config.SymbolsToLocalize.empty() &&
-           is_contained(Config.SymbolsToLocalize, Sym.Name)))
+      if (!Sym.isCommon() &&
+          ((Config.LocalizeHidden &&
+            (Sym.Visibility == STV_HIDDEN || Sym.Visibility == STV_INTERNAL)) ||
+           (!Config.SymbolsToLocalize.empty() &&
+            is_contained(Config.SymbolsToLocalize, Sym.Name))))
         Sym.Binding = STB_LOCAL;
 
       // Note: these two globalize flags have very similar names but different

llvm/tools/llvm-objcopy/ELF/Object.cpp

@@ -332,6 +332,8 @@ uint16_t Symbol::getShndx() const {
   llvm_unreachable("Symbol with invalid ShndxType encountered");
 }
 
+bool Symbol::isCommon() const { return getShndx() == SHN_COMMON; }
+
 void SymbolTableSection::assignIndices() {
   uint32_t Index = 0;
   for (auto &Sym : Symbols)

llvm/tools/llvm-objcopy/ELF/Object.h

@@ -415,6 +415,7 @@ struct Symbol {
   bool Referenced = false;
 
   uint16_t getShndx() const;
+  bool isCommon() const;
 };
 
 class SectionIndexSection : public SectionBase {