Handle section vs global name conflict.

This is a fix for PR26941.

When there is both a section and a global definition with the same
name, the global wins.

Section symbols are not added to the symbol table; section references
are left undefined and fixed up in the object writer unless they've
been satisfied by some other definition.

llvm-svn: 264649

2 files changed, 23 insertions, 15 deletions

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 01b7148cea7..68c3cb13a1b 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -375,9 +375,24 @@ uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
 
 void ELFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
                                                const MCAsmLayout &Layout) {
+  // Section symbols are used as definitions for undefined symbols with matching
+  // names. If there are multiple sections with the same name, the first one is
+  // used.
+  for (const MCSection &Sec : Asm) {
+    const MCSymbol *Begin = Sec.getBeginSymbol();
+    if (!Begin)
+      continue;
+
+    const MCSymbol *Alias = Asm.getContext().lookupSymbol(Begin->getName());
+    if (!Alias || !Alias->isUndefined())
+      continue;
+
+    Renames.insert(
+        std::make_pair(cast<MCSymbolELF>(Alias), cast<MCSymbolELF>(Begin)));
+  }
+
   // The presence of symbol versions causes undefined symbols and
   // versions declared with @@@ to be renamed.
-
   for (const MCSymbol &A : Asm.symbols()) {
     const auto &Alias = cast<MCSymbolELF>(A);
     // Not an alias.
diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 96e24de6b4d..e326738325a 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -124,19 +124,9 @@ MCSymbolELF *MCContext::getOrCreateSectionSymbol(const MCSectionELF &Section) {
     return Sym;
 
   StringRef Name = Section.getSectionName();
-
-  MCSymbol *&OldSym = Symbols[Name];
-  if (OldSym && OldSym->isUndefined()) {
-    Sym = cast<MCSymbolELF>(OldSym);
-    return Sym;
-  }
-
-  auto NameIter = UsedNames.insert(std::make_pair(Name, true)).first;
+  auto NameIter = UsedNames.insert(std::make_pair(Name, false)).first;
   Sym = new (&*NameIter, *this) MCSymbolELF(&*NameIter, /*isTemporary*/ false);
 
-  if (!OldSym)
-    OldSym = Sym;
-
   return Sym;
 }
 
@@ -192,9 +182,12 @@ MCSymbol *MCContext::createSymbol(StringRef Name, bool AlwaysAddSuffix,
       raw_svector_ostream(NewName) << NextUniqueID++;
     }
     auto NameEntry = UsedNames.insert(std::make_pair(NewName, true));
-    if (NameEntry.second) {
-      // Ok, we found a name. Have the MCSymbol object itself refer to the copy
-      // of the string that is embedded in the UsedNames entry.
+    if (NameEntry.second || !NameEntry.first->second) {
+      // Ok, we found a name.
+      // Mark it as used for a non-section symbol.
+      NameEntry.first->second = true;
+      // Have the MCSymbol object itself refer to the copy of the string that is
+      // embedded in the UsedNames entry.
       return createSymbolImpl(&*NameEntry.first, IsTemporary);
     }
     assert(IsTemporary && "Cannot rename non-temporary symbols");