[WebAssembly] Support weak defined symbols

Model weakly defined symbols as symbols that are both
exports and imported and marked as weak. Local references
to the symbols refer to the import but the linker can
resolve this to the weak export if not strong symbol
is found at link time.

Differential Revision: https://reviews.llvm.org/D35029

llvm-svn: 307348

1 files changed, 20 insertions, 10 deletions

diff --git a/llvm/lib/Object/WasmObjectFile.cpp b/llvm/lib/Object/WasmObjectFile.cpp
index fff497ba556..3c675aa71b9 100644
--- a/llvm/lib/Object/WasmObjectFile.cpp
+++ b/llvm/lib/Object/WasmObjectFile.cpp
@@ -567,20 +567,16 @@ Error WasmObjectFile::parseExportSection(const uint8_t *Ptr, const uint8_t *End)
     Ex.Name = readString(Ptr);
     Ex.Kind = readUint8(Ptr);
     Ex.Index = readVaruint32(Ptr);
+    WasmSymbol::SymbolType ExportType;
+    bool MakeSymbol = false;
     switch (Ex.Kind) {
     case wasm::WASM_EXTERNAL_FUNCTION:
-      SymbolMap.try_emplace(Ex.Name, Symbols.size());
-      Symbols.emplace_back(Ex.Name, WasmSymbol::SymbolType::FUNCTION_EXPORT,
-                           Sections.size(), i);
-      DEBUG(dbgs() << "Adding export: " << Symbols.back()
-                   << " sym index:" << Symbols.size() << "\n");
+      ExportType = WasmSymbol::SymbolType::FUNCTION_EXPORT;
+      MakeSymbol = true;
       break;
     case wasm::WASM_EXTERNAL_GLOBAL:
-      SymbolMap.try_emplace(Ex.Name, Symbols.size());
-      Symbols.emplace_back(Ex.Name, WasmSymbol::SymbolType::GLOBAL_EXPORT,
-                           Sections.size(), i);
-      DEBUG(dbgs() << "Adding export: " << Symbols.back()
-                   << " sym index:" << Symbols.size() << "\n");
+      ExportType = WasmSymbol::SymbolType::GLOBAL_EXPORT;
+      MakeSymbol = true;
       break;
     case wasm::WASM_EXTERNAL_MEMORY:
     case wasm::WASM_EXTERNAL_TABLE:
@@ -589,6 +585,20 @@ Error WasmObjectFile::parseExportSection(const uint8_t *Ptr, const uint8_t *End)
       return make_error<GenericBinaryError>(
           "Unexpected export kind", object_error::parse_failed);
     }
+    if (MakeSymbol) {
+      auto Pair = SymbolMap.try_emplace(Ex.Name, Symbols.size());
+      if (Pair.second) {
+        Symbols.emplace_back(Ex.Name, ExportType,
+                             Sections.size(), i);
+        DEBUG(dbgs() << "Adding export: " << Symbols.back()
+                     << " sym index:" << Symbols.size() << "\n");
+      } else {
+        uint32_t SymIndex = Pair.first->second;
+        Symbols[SymIndex] = WasmSymbol(Ex.Name, ExportType, Sections.size(), i);
+        DEBUG(dbgs() << "Replacing existing symbol:  " << Symbols[SymIndex]
+                     << " sym index:" << SymIndex << "\n");
+      }
+    }
     Exports.push_back(Ex);
   }
   if (Ptr != End)