[lld][WebAssembly] Fix static linking of -fPIC code with external undefined functions

[sbc100]

• fixes

[ruiu]

LGTM

lld/test/wasm/pic-static.ll

 ; Test that PIC code can be linked into static binaries.
 ; In this case the GOT entries will end up as internalized wasm globals with
 ; fixed values.
 ; RUN: llc -relocation-model=pic -filetype=obj %p/Inputs/ret32.ll -o %t.ret32.o
 ; RUN: llc -relocation-model=pic -filetype=obj %s -o %t.o
-; RUN: wasm-ld -o %t.wasm %t.o %t.ret32.o
+; RUN: wasm-ld --allow-undefined --export-all -o %t.wasm %t.o %t.ret32.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 target triple = "wasm32-unknown-emscripten"
 
 declare i32 @ret32(float)
+declare i32 @missing_function(float)
 @global_float = global float 1.0
 @hidden_float = hidden global float 2.0
 
 @ret32_ptr = global i32 (float)* @ret32, align 4
 
 define i32 (float)* @getaddr_external() {
   ret i32 (float)* @ret32;
 }
 
+define i32 (float)* @getaddr_missing_function() {
+  ret i32 (float)* @missing_function;
+}
+
 define i32 ()* @getaddr_hidden() {
   ret i32 ()* @hidden_func;
 }
 
 define hidden i32 @hidden_func() {
   ret i32 1
 }
 

 ; CHECK-NEXT:           Value:           66576
 
 ; GOT.func.ret32
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1
+
+; GOT.func.missing_function
+; CHECK-NEXT:       - Index:           2
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           2
 
 ; __table_base
-; CHECK-NEXT:       - Index:           2
+; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1
 
 ; GOT.mem.global_float
-; CHECK-NEXT:       - Index:           3
+; CHECK-NEXT:       - Index:           4
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024
 
 ; GOT.mem.ret32_ptr
-; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1032
 
 ; __memory_base
-; CHECK-NEXT:       - Index:           5
+; CHECK-NEXT:       - Index:           6
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024

lld/wasm/InputFiles.cpp

if (reloc.Type != R_WASM_TYPE_INDEX_LEB) {
     // in debug sections.
     if ((isa<FunctionSymbol>(sym) || isa<DataSymbol>(sym)) && !sym->isLive())
       return 0;
   }
 
   switch (reloc.Type) {
   case R_WASM_TABLE_INDEX_I32:
   case R_WASM_TABLE_INDEX_SLEB:
-  case R_WASM_TABLE_INDEX_REL_SLEB:
+  case R_WASM_TABLE_INDEX_REL_SLEB: {
     if (!getFunctionSymbol(reloc.Index)->hasTableIndex())
       return 0;
-    return getFunctionSymbol(reloc.Index)->getTableIndex();
+    uint32_t index = getFunctionSymbol(reloc.Index)->getTableIndex();
+    if (reloc.Type == R_WASM_TABLE_INDEX_REL_SLEB)
+      index -= config->tableBase;
+    return index;
+
+  }
   case R_WASM_MEMORY_ADDR_SLEB:
   case R_WASM_MEMORY_ADDR_I32:
   case R_WASM_MEMORY_ADDR_LEB:
   case R_WASM_MEMORY_ADDR_REL_SLEB:
     if (isa<UndefinedData>(sym))
       return 0;
     return cast<DefinedData>(sym)->getVirtualAddress() + reloc.Addend;
   case R_WASM_TYPE_INDEX_LEB:

lld/wasm/Relocations.cpp

static void addGOTEntry(Symbol *sym) {
   // In non-PIC mode (i.e. when code compiled as fPIC is linked into a static
   // binary) we create an internal wasm global with a fixed value that takes the
   // place of th GOT entry and effectivly acts as an i32 const. This can
   // potentially be optimized away at runtime or with a post-link tool.
   // TODO(sbc): Linker relaxation might also be able to optimize this away.
   if (config->isPic)
     out.importSec->addGOTEntry(sym);
   else
-    out.globalSec->addDummyGOTEntry(sym);
+    out.globalSec->addStaticGOTEntry(sym);
 }
 
 void lld::wasm::scanRelocations(InputChunk *chunk) {
   if (!chunk->live)
     return;
   ObjFile *file = chunk->file;
   ArrayRef<WasmSignature> types = file->getWasmObj()->types();
   for (const WasmRelocation &reloc : chunk->getRelocations()) {

lld/wasm/Symbols.h

public:
   uint32_t getOutputSymbolIndex() const;
   void setOutputSymbolIndex(uint32_t index);
 
   WasmSymbolType getWasmType() const;
   bool isExported() const;
 
   const WasmSignature* getSignature() const;
 
-  bool isInGOT() const { return gotIndex != INVALID_INDEX; }
-
   uint32_t getGOTIndex() const {
     assert(gotIndex != INVALID_INDEX);
     return gotIndex;
   }
 
   void setGOTIndex(uint32_t index);
   bool hasGOTIndex() const { return gotIndex != INVALID_INDEX; }
 
 protected:
   Symbol(StringRef name, Kind k, uint32_t flags, InputFile *f)
       : name(name), file(f), flags(flags), symbolKind(k),
-        referenced(!config->gcSections), isUsedInRegularObj(false),
-        forceExport(false), canInline(false), traced(false) {}
+        referenced(!config->gcSections), requiresGOT(false),
+        isUsedInRegularObj(false), forceExport(false), canInline(false),
+        traced(false) {}
 
   StringRef name;
   InputFile *file;
   uint32_t flags;
   uint32_t outputSymbolIndex = INVALID_INDEX;
   uint32_t gotIndex = INVALID_INDEX;
   Kind symbolKind;
 
 public:
   bool referenced : 1;
 
+  // True for data symbols that needs a dummy GOT entry.  Used for static
+  // linking of GOT accesses.
+  bool requiresGOT : 1;
+
   // True if the symbol was used for linking and thus need to be added to the
   // output file's symbol table. This is true for all symbols except for
   // unreferenced DSO symbols, lazy (archive) symbols, and bitcode symbols that
   // are unreferenced except by other bitcode objects.
   bool isUsedInRegularObj : 1;
 
   // True if ths symbol is explicity marked for export (i.e. via the -e/--export
   // command line flag)

lld/wasm/SyntheticSections.h

public:
 
   void writeBody() override;
 };
 
 class GlobalSection : public SyntheticSection {
 public:
   GlobalSection() : SyntheticSection(llvm::wasm::WASM_SEC_GLOBAL) {}
   uint32_t numGlobals() const {
-    return inputGlobals.size() + definedFakeGlobals.size() + gotSymbols.size();
+    return inputGlobals.size() + definedFakeGlobals.size() +
+           staticGotSymbols.size();
   }
   bool isNeeded() const override { return numGlobals() > 0; }
   void assignIndexes() override;
   void writeBody() override;
   void addGlobal(InputGlobal *global);
-  void addDummyGOTEntry(Symbol *sym);
+  void addStaticGOTEntry(Symbol *sym);
 
   std::vector<const DefinedData *> definedFakeGlobals;
   std::vector<InputGlobal *> inputGlobals;
-  std::vector<Symbol *> gotSymbols;
+  std::vector<Symbol *> staticGotSymbols;
 };
 
 // The event section contains a list of declared wasm events associated with the
 // module. Currently the only supported event kind is exceptions. A single event
 // entry represents a single event with an event tag. All C++ exceptions are
 // represented by a single event. An event entry in this section contains
 // information on what kind of event it is (e.g. exception) and the type of
 // values contained in a single event object. (In wasm, an event can contain

lld/wasm/SyntheticSections.cpp

if (config->importMemory)
     ++numImports;
   if (config->importTable)
     ++numImports;
   return numImports;
 }
 
 void ImportSection::addGOTEntry(Symbol *sym) {
   assert(!isSealed);
-  LLVM_DEBUG(dbgs() << "addGOTEntry: " << toString(*sym) << "\n");
   if (sym->hasGOTIndex())
     return;
+  LLVM_DEBUG(dbgs() << "addGOTEntry: " << toString(*sym) << "\n");
   sym->setGOTIndex(numImportedGlobals++);
   gotSymbols.push_back(sym);
 }
 
 void ImportSection::addImport(Symbol *sym) {
   assert(!isSealed);
   importedSymbols.emplace_back(sym);
   if (auto *f = dyn_cast<FunctionSymbol>(sym))
void MemorySection::writeBody() {
   if (hasMax)
     writeUleb128(os, maxMemoryPages, "max pages");
 }
 
 void GlobalSection::assignIndexes() {
   uint32_t globalIndex = out.importSec->getNumImportedGlobals();
   for (InputGlobal *g : inputGlobals)
     g->setGlobalIndex(globalIndex++);
-  for (Symbol *sym : gotSymbols)
+  for (Symbol *sym : staticGotSymbols)
     sym->setGOTIndex(globalIndex++);
 }
 
-void GlobalSection::addDummyGOTEntry(Symbol *sym) {
-  LLVM_DEBUG(dbgs() << "addDummyGOTEntry: " << toString(*sym) << "\n");
-  if (sym->hasGOTIndex())
+void GlobalSection::addStaticGOTEntry(Symbol *sym) {
+  if (sym->requiresGOT)
     return;
-  gotSymbols.push_back(sym);
+  LLVM_DEBUG(dbgs() << "addStaticGOTEntry: " << sym->getName() << " "
+                    << toString(sym->kind()) << "\n");
+  sym->requiresGOT = true;
+  if (auto *F = dyn_cast<FunctionSymbol>(sym))
+    out.elemSec->addEntry(F);
+  staticGotSymbols.push_back(sym);
 }
 
 void GlobalSection::writeBody() {
   raw_ostream &os = bodyOutputStream;
 
   writeUleb128(os, numGlobals(), "global count");
   for (InputGlobal *g : inputGlobals)
     writeGlobal(os, g->global);
-  for (const DefinedData *sym : definedFakeGlobals) {
+  for (const Symbol *sym : staticGotSymbols) {
     WasmGlobal global;
     global.Type = {WASM_TYPE_I32, false};
     global.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
-    global.InitExpr.Value.Int32 = sym->getVirtualAddress();
+    if (auto *d = dyn_cast<DefinedData>(sym))
+      global.InitExpr.Value.Int32 = d->getVirtualAddress();
+    else if (auto *f = cast<FunctionSymbol>(sym))
+      global.InitExpr.Value.Int32 = f->getTableIndex();
     writeGlobal(os, global);
   }
-  for (const Symbol *sym : gotSymbols) {
+  for (const DefinedData *sym : definedFakeGlobals) {
     WasmGlobal global;
     global.Type = {WASM_TYPE_I32, false};
     global.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
-    if (auto *d = dyn_cast<DefinedData>(sym))
-      global.InitExpr.Value.Int32 = d->getVirtualAddress();
-    else if (auto *f = cast<DefinedFunction>(sym))
-      global.InitExpr.Value.Int32 = f->getTableIndex();
+    global.InitExpr.Value.Int32 = sym->getVirtualAddress();
     writeGlobal(os, global);
   }
 }
 
 void GlobalSection::addGlobal(InputGlobal *global) {
   if (!global->live)
     return;
   inputGlobals.push_back(global);

lld/wasm/Writer.cpp

void Writer::calculateExports() {
   if (!config->relocatable && !config->importMemory)
     out.exportSec->exports.push_back(
         WasmExport{"memory", WASM_EXTERNAL_MEMORY, 0});
 
   if (!config->relocatable && config->exportTable)
     out.exportSec->exports.push_back(
         WasmExport{functionTableName, WASM_EXTERNAL_TABLE, 0});
 
-  unsigned fakeGlobalIndex = out.importSec->getNumImportedGlobals() +
-                             out.globalSec->inputGlobals.size();
+  unsigned fakeGlobalIndex = out.globalSec->numGlobals();
 
   for (Symbol *sym : symtab->getSymbols()) {
     if (!sym->isExported())
       continue;
     if (!sym->isLive())
       continue;
 
     StringRef name = sym->getName();