[WebAssembly] Make __attribute__((used)) not imply export.

Add an WASM_SYMBOL_NO_STRIP flag, so that __attribute__((used)) doesn't need to imply exporting. When targeting Emscripten, have WASM_SYMBOL_NO_STRIP imply exporting. Differential Revision: https://reviews.llvm.org/D62542 llvm-svn: 370415
llvm · Aug 29, 2019 · da84b68 · da84b68
1 parent 452e564
commit da84b68
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Showing 12 changed files with 39 additions and 18 deletions.
diff --git a/llvm/include/llvm/BinaryFormat/Wasm.h b/llvm/include/llvm/BinaryFormat/Wasm.h
@@ -318,6 +318,7 @@ const unsigned WASM_SYMBOL_VISIBILITY_HIDDEN = 0x4;
 const unsigned WASM_SYMBOL_UNDEFINED = 0x10;
 const unsigned WASM_SYMBOL_EXPORTED = 0x20;
 const unsigned WASM_SYMBOL_EXPLICIT_NAME = 0x40;
+const unsigned WASM_SYMBOL_NO_STRIP = 0x80;
 
 #define WASM_RELOC(name, value) name = value,
 

diff --git a/llvm/include/llvm/MC/MCSymbolWasm.h b/llvm/include/llvm/MC/MCSymbolWasm.h
@@ -54,6 +54,13 @@ class MCSymbolWasm : public MCSymbol {
     modifyFlags(wasm::WASM_SYMBOL_EXPORTED, wasm::WASM_SYMBOL_EXPORTED);
   }
 
+  bool isNoStrip() const {
+    return getFlags() & wasm::WASM_SYMBOL_NO_STRIP;
+  }
+  void setNoStrip() const {
+    modifyFlags(wasm::WASM_SYMBOL_NO_STRIP, wasm::WASM_SYMBOL_NO_STRIP);
+  }
+
   bool isWeak() const { return IsWeak; }
   void setWeak(bool isWeak) { IsWeak = isWeak; }
 

diff --git a/llvm/include/llvm/MC/MCWasmObjectWriter.h b/llvm/include/llvm/MC/MCWasmObjectWriter.h
@@ -20,9 +20,10 @@ class raw_pwrite_stream;
 
 class MCWasmObjectTargetWriter : public MCObjectTargetWriter {
   const unsigned Is64Bit : 1;
+  const unsigned IsEmscripten : 1;
 
 protected:
-  explicit MCWasmObjectTargetWriter(bool Is64Bit_);
+  explicit MCWasmObjectTargetWriter(bool Is64Bit_, bool IsEmscripten);
 
 public:
   virtual ~MCWasmObjectTargetWriter();
@@ -38,6 +39,7 @@ class MCWasmObjectTargetWriter : public MCObjectTargetWriter {
   /// \name Accessors
   /// @{
   bool is64Bit() const { return Is64Bit; }
+  bool isEmscripten() const { return IsEmscripten; }
   /// @}
 };
 

diff --git a/llvm/lib/MC/MCWasmObjectTargetWriter.cpp b/llvm/lib/MC/MCWasmObjectTargetWriter.cpp
@@ -10,8 +10,9 @@
 
 using namespace llvm;
 
-MCWasmObjectTargetWriter::MCWasmObjectTargetWriter(bool Is64Bit)
-    : Is64Bit(Is64Bit) {}
+MCWasmObjectTargetWriter::MCWasmObjectTargetWriter(bool Is64Bit,
+                                                   bool IsEmscripten)
+    : Is64Bit(Is64Bit), IsEmscripten(IsEmscripten) {}
 
 // Pin the vtable to this object file
 MCWasmObjectTargetWriter::~MCWasmObjectTargetWriter() = default;
diff --git a/llvm/lib/MC/MCWasmStreamer.cpp b/llvm/lib/MC/MCWasmStreamer.cpp
@@ -122,7 +122,7 @@ bool MCWasmStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
     break;
 
   case MCSA_NoDeadStrip:
-    Symbol->setExported();
+    Symbol->setNoStrip();
     break;
 
   default:

diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -258,6 +258,7 @@ class WasmObjectWriter : public MCObjectWriter {
 
   // TargetObjectWriter wrappers.
   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
+  bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); }
 
   void startSection(SectionBookkeeping &Section, unsigned SectionId);
   void startCustomSection(SectionBookkeeping &Section, StringRef Name);
@@ -1443,8 +1444,12 @@ uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
       Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
     if (WS.isUndefined())
       Flags |= wasm::WASM_SYMBOL_UNDEFINED;
-    if (WS.isExported())
-      Flags |= wasm::WASM_SYMBOL_EXPORTED;
+    if (WS.isNoStrip()) {
+      Flags |= wasm::WASM_SYMBOL_NO_STRIP;
+      if (isEmscripten()) {
+        Flags |= wasm::WASM_SYMBOL_EXPORTED;
+      }
+    }
     if (WS.getName() != WS.getImportName())
       Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
 

diff --git a/llvm/lib/ObjectYAML/WasmYAML.cpp b/llvm/lib/ObjectYAML/WasmYAML.cpp
@@ -535,6 +535,7 @@ void ScalarBitSetTraits<WasmYAML::SymbolFlags>::bitset(
   BCaseMask(UNDEFINED, UNDEFINED);
   BCaseMask(EXPORTED, EXPORTED);
   BCaseMask(EXPLICIT_NAME, EXPLICIT_NAME);
+  BCaseMask(NO_STRIP, NO_STRIP);
 #undef BCaseMask
 }
 

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp
@@ -31,10 +31,12 @@ namespace {
 
 class WebAssemblyAsmBackend final : public MCAsmBackend {
   bool Is64Bit;
+  bool IsEmscripten;
 
 public:
-  explicit WebAssemblyAsmBackend(bool Is64Bit)
-      : MCAsmBackend(support::little), Is64Bit(Is64Bit) {}
+  explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
+      : MCAsmBackend(support::little), Is64Bit(Is64Bit),
+        IsEmscripten(IsEmscripten) {}
 
   unsigned getNumFixupKinds() const override {
     return WebAssembly::NumTargetFixupKinds;
@@ -123,11 +125,11 @@ void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
 
 std::unique_ptr<MCObjectTargetWriter>
 WebAssemblyAsmBackend::createObjectTargetWriter() const {
-  return createWebAssemblyWasmObjectWriter(Is64Bit);
+  return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
 }
 
 } // end anonymous namespace
 
 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
-  return new WebAssemblyAsmBackend(TT.isArch64Bit());
+  return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
 }
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
@@ -38,7 +38,7 @@ MCCodeEmitter *createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII);
 MCAsmBackend *createWebAssemblyAsmBackend(const Triple &TT);
 
 std::unique_ptr<MCObjectTargetWriter>
-createWebAssemblyWasmObjectWriter(bool Is64Bit);
+createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten);
 
 namespace WebAssembly {
 enum OperandType {

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp
@@ -31,16 +31,17 @@ using namespace llvm;
 namespace {
 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter {
 public:
-  explicit WebAssemblyWasmObjectWriter(bool Is64Bit);
+  explicit WebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten);
 
 private:
   unsigned getRelocType(const MCValue &Target,
                         const MCFixup &Fixup) const override;
 };
 } // end anonymous namespace
 
-WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit)
-    : MCWasmObjectTargetWriter(Is64Bit) {}
+WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit,
+                                                         bool IsEmscripten)
+    : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {}
 
 static const MCSection *getFixupSection(const MCExpr *Expr) {
   if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
@@ -116,6 +117,6 @@ unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
 }
 
 std::unique_ptr<MCObjectTargetWriter>
-llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) {
-  return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit);
+llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
+  return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
 }
diff --git a/llvm/test/MC/WebAssembly/no-dead-strip.ll b/llvm/test/MC/WebAssembly/no-dead-strip.ll
@@ -13,8 +13,8 @@ entry:
 ; CHECK-NEXT:   Symbol {
 ; CHECK-NEXT:     Name: foo
 ; CHECK-NEXT:     Type: FUNCTION (0x0)
-; CHECK-NEXT:     Flags [ (0x20)
-; CHECK-NEXT:       EXPORTED (0x20)
+; CHECK-NEXT:     Flags [ (0x80)
+; CHECK-NEXT:       NO_STRIP (0x80)
 ; CHECK-NEXT:     ]
 ; CHECK-NEXT:     ElementIndex: 0x0
 ; CHECK-NEXT:   }

diff --git a/llvm/tools/llvm-readobj/WasmDumper.cpp b/llvm/tools/llvm-readobj/WasmDumper.cpp
@@ -51,6 +51,7 @@ static const EnumEntry<unsigned> WasmSymbolFlags[] = {
   ENUM_ENTRY(UNDEFINED),
   ENUM_ENTRY(EXPORTED),
   ENUM_ENTRY(EXPLICIT_NAME),
+  ENUM_ENTRY(NO_STRIP),
 #undef ENUM_ENTRY
 };