Merging r368310:

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r368310 | sbc | 2019-08-08 09:58:36 -0700 (Thu, 08 Aug 2019) | 11 lines

[lld][WebAssembly] Add optional symbols after input file handling

This allows undefined references in input files be resolved by the
optional symbols.  Previously we were doing this before input file
reading which means it was working only for command line symbols
references (i.e. -u or --export).

Also use addOptionalDataSymbol for __dso_handle and make all optional
symbols hidden by default.

Differential Revision: https://reviews.llvm.org/D65920
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lld/test/wasm/global-base.test

@@ -24,11 +24,7 @@ CHECK-1024-NEXT:          Opcode:          I32_CONST
 CHECK-1024-NEXT:          Value:           1024
 
 CHECK-1024:       - Type:            EXPORT
-CHECK-1024-NEXT:    Exports:
-CHECK-1024-NEXT:      - Name:            memory
-CHECK-1024-NEXT:        Kind:            MEMORY
-CHECK-1024-NEXT:        Index:           0
-CHECK-1024-NEXT:      - Name:            __data_end
+CHECK-1024:           - Name:            __data_end
 CHECK-1024-NEXT:        Kind:            GLOBAL
 CHECK-1024-NEXT:        Index:           1
 CHECK-1024-NEXT:      - Name:            __global_base
@@ -59,11 +55,7 @@ CHECK-16777216-NEXT:          Opcode:          I32_CONST
 CHECK-16777216-NEXT:          Value:           16777216
 
 CHECK-16777216:       - Type:            EXPORT
-CHECK-16777216-NEXT:    Exports:
-CHECK-16777216-NEXT:      - Name:            memory
-CHECK-16777216-NEXT:        Kind:            MEMORY
-CHECK-16777216-NEXT:        Index:           0
-CHECK-16777216-NEXT:      - Name:            __data_end
+CHECK-16777216:           - Name:            __data_end
 CHECK-16777216-NEXT:        Kind:            GLOBAL
 CHECK-16777216-NEXT:        Index:           1
 CHECK-16777216-NEXT:      - Name:            __global_base

lld/test/wasm/optional-symbol.ll

@@ -0,0 +1,14 @@
+; RUN: llc -filetype=obj -o %t.o %s
+; RUN: wasm-ld --export=get_handle %t.o -o %t.wasm
+
+target triple = "wasm32-unknown-unknown"
+
+@__dso_handle = external global i8*
+
+define i8** @get_handle() {
+  ret i8** @__dso_handle
+}
+
+define void @_start() {
+  ret void
+}

lld/test/wasm/stack-first.test

@@ -32,12 +32,12 @@ CHECK-NEXT:     Exports:
 CHECK-NEXT:       - Name:            memory
 CHECK-NEXT:         Kind:            MEMORY
 CHECK-NEXT:         Index:           0
+CHECK-NEXT:       - Name:            _start
+CHECK-NEXT:         Kind:            FUNCTION
+CHECK-NEXT:         Index:           0
 CHECK-NEXT:       - Name:            __data_end
 CHECK-NEXT:         Kind:            GLOBAL
 CHECK-NEXT:         Index:           1
 CHECK-NEXT:       - Name:            __heap_base
 CHECK-NEXT:         Kind:            GLOBAL
 CHECK-NEXT:         Index:           2
-CHECK-NEXT:       - Name:            _start
-CHECK-NEXT:         Kind:            FUNCTION
-CHECK-NEXT:         Index:           0

lld/wasm/Driver.cpp

@@ -482,8 +482,6 @@ static void createSyntheticSymbols() {
     }
   }
 
-  if (!config->shared)
-    WasmSym::dataEnd = symtab->addOptionalDataSymbol("__data_end");
 
   if (config->isPic) {
     WasmSym::stackPointer =
@@ -512,8 +510,6 @@ static void createSyntheticSymbols() {
     // See: https://github.com/WebAssembly/mutable-global
     WasmSym::stackPointer = symtab->addSyntheticGlobal(
         "__stack_pointer", WASM_SYMBOL_VISIBILITY_HIDDEN, stackPointer);
-    WasmSym::globalBase = symtab->addOptionalDataSymbol("__global_base");
-    WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
   }
 
   if (config->sharedMemory && !config->shared) {
@@ -539,9 +535,17 @@ static void createSyntheticSymbols() {
         "__wasm_init_tls", WASM_SYMBOL_VISIBILITY_HIDDEN,
         make<SyntheticFunction>(i32ArgSignature, "__wasm_init_tls"));
   }
+}
+
+static void createOptionalSymbols() {
+  if (!config->relocatable)
+    WasmSym::dsoHandle = symtab->addOptionalDataSymbol("__dso_handle");
 
-  WasmSym::dsoHandle = symtab->addSyntheticDataSymbol(
-      "__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
+  if (!config->isPic) {
+    WasmSym::dataEnd = symtab->addOptionalDataSymbol("__data_end");
+    WasmSym::globalBase = symtab->addOptionalDataSymbol("__global_base");
+    WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
+  }
 }
 
 // Reconstructs command line arguments so that so that you can re-run
@@ -724,6 +728,8 @@ void LinkerDriver::link(ArrayRef<const char *> argsArr) {
   if (errorCount())
     return;
 
+  createOptionalSymbols();
+
   // Handle the `--undefined <sym>` options.
   for (auto *arg : args.filtered(OPT_undefined))
     handleUndefined(arg->getValue());

lld/wasm/SymbolTable.cpp

@@ -205,15 +205,15 @@ DefinedFunction *SymbolTable::addSyntheticFunction(StringRef name,
 // Adds an optional, linker generated, data symbols.  The symbol will only be
 // added if there is an undefine reference to it, or if it is explictly exported
 // via the --export flag.  Otherwise we don't add the symbol and return nullptr.
-DefinedData *SymbolTable::addOptionalDataSymbol(StringRef name, uint32_t value,
-                                                uint32_t flags) {
+DefinedData *SymbolTable::addOptionalDataSymbol(StringRef name,
+                                                uint32_t value) {
   Symbol *s = find(name);
   if (!s && (config->exportAll || config->exportedSymbols.count(name) != 0))
     s = insertName(name).first;
   else if (!s || s->isDefined())
     return nullptr;
   LLVM_DEBUG(dbgs() << "addOptionalDataSymbol: " << name << "\n");
-  auto *rtn = replaceSymbol<DefinedData>(s, name, flags);
+  auto *rtn = replaceSymbol<DefinedData>(s, name, WASM_SYMBOL_VISIBILITY_HIDDEN);
   rtn->setVirtualAddress(value);
   rtn->referenced = true;
   return rtn;

lld/wasm/SymbolTable.h

@@ -77,8 +77,7 @@ class SymbolTable {
                                     InputGlobal *global);
   DefinedFunction *addSyntheticFunction(StringRef name, uint32_t flags,
                                         InputFunction *function);
-  DefinedData *addOptionalDataSymbol(StringRef name, uint32_t value = 0,
-                                     uint32_t flags = 0);
+  DefinedData *addOptionalDataSymbol(StringRef name, uint32_t value = 0);
 
   void handleSymbolVariants();
   void handleWeakUndefines();