[WebAssembly] Import __stack_pointer when building -pie binaries

[sbc100]

Summary

The -pie binary doesn't know that layout ahead of time so needs to
import the stack pointer from the embedder, just like we do already
for shared libraries.

This change is needed in order to address:
https://github.com/emscripten-core/emscripten/issues/8915

[sbc100]

• fix typo

[ruiu]

LGTM

[sbc100]

• rebase

lld/test/wasm/pie.ll

 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           __indirect_function_table
 ; CHECK-NEXT:         Kind:            TABLE
 ; CHECK-NEXT:         Table:
 ; CHECK-NEXT:           ElemType:        FUNCREF
 ; CHECK-NEXT:           Limits:
 ; CHECK-NEXT:             Initial:         0x00000001
 ; CHECK-NEXT:       - Module:          env
+; CHECK-NEXT:         Field:           __stack_pointer
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         GlobalType:      I32
+; CHECK-NEXT:         GlobalMutable:   true
+; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           __memory_base
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         GlobalType:      I32
 ; CHECK-NEXT:         GlobalMutable:   false
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           __table_base
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         GlobalType:      I32
 ; CHECK-NEXT:         GlobalMutable:   false
 
 

lld/wasm/Driver.cpp

if (config->isPic) {
       // For PIC code we create a synthetic function __wasm_apply_relocs which
       // is called from __wasm_call_ctors before the user-level constructors.
       WasmSym::applyRelocs = symtab->addSyntheticFunction(
           "__wasm_apply_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
           make<SyntheticFunction>(nullSignature, "__wasm_apply_relocs"));
     }
   }
 
-  // The __stack_pointer is imported in the shared library case, and exported
-  // in the non-shared (executable) case.
-  if (config->shared) {
+  if (!config->shared)
+    WasmSym::dataEnd = symtab->addOptionalDataSymbol("__data_end");
+
+  if (config->isPic) {
     WasmSym::stackPointer =
         createUndefinedGlobal("__stack_pointer", &mutableGlobalTypeI32);
+    // For PIC code, we import two global variables (__memory_base and
+    // __table_base) from the environment and use these as the offset at
+    // which to load our static data and function table.
+    // See:
+    // https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
+    WasmSym::memoryBase =
+        createUndefinedGlobal("__memory_base", &globalTypeI32);
+    WasmSym::tableBase = createUndefinedGlobal("__table_base", &globalTypeI32);
+    WasmSym::memoryBase->markLive();
+    WasmSym::tableBase->markLive();
   } else {
     llvm::wasm::WasmGlobal global;
     global.Type = {WASM_TYPE_I32, true};
     global.InitExpr.Value.Int32 = 0;
     global.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
     global.SymbolName = "__stack_pointer";
     auto *stackPointer = make<InputGlobal>(global, nullptr);
     stackPointer->live = true;
     // For non-PIC code
     // TODO(sbc): Remove WASM_SYMBOL_VISIBILITY_HIDDEN when the mutable global
     // spec proposal is implemented in all major browsers.
     // See: https://github.com/WebAssembly/mutable-global
     WasmSym::stackPointer = symtab->addSyntheticGlobal(
         "__stack_pointer", WASM_SYMBOL_VISIBILITY_HIDDEN, stackPointer);
-    WasmSym::dataEnd = symtab->addOptionalDataSymbol("__data_end");
     WasmSym::globalBase = symtab->addOptionalDataSymbol("__global_base");
     WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
   }
 
-  if (config->isPic) {
-    // For PIC code, we import two global variables (__memory_base and
-    // __table_base) from the environment and use these as the offset at
-    // which to load our static data and function table.
-    // See:
-    // https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
-    WasmSym::memoryBase =
-        createUndefinedGlobal("__memory_base", &globalTypeI32);
-    WasmSym::tableBase = createUndefinedGlobal("__table_base", &globalTypeI32);
-    WasmSym::memoryBase->markLive();
-    WasmSym::tableBase->markLive();
-  }
-
   WasmSym::dsoHandle = symtab->addSyntheticDataSymbol(
       "__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
 }
 
 // Reconstructs command line arguments so that so that you can re-run
 // the same command with the same inputs. This is for --reproduce.
 static std::string createResponseFile(const opt::InputArgList &args) {
   SmallString<0> data;

lld/wasm/Writer.cpp

 // The --stack-first option means that stack is placed before any static data.
 // This can be useful since it means that stack overflow traps immediately
 // rather than overwriting global data, but also increases code size since all
 // static data loads and stores requires larger offsets.
 void Writer::layoutMemory() {
   uint32_t memoryPtr = 0;
 
   auto placeStack = [&]() {
-    if (config->relocatable || config->shared)
+    if (config->relocatable || config->isPic)
       return;
     memoryPtr = alignTo(memoryPtr, stackAlignment);
     if (config->zStackSize != alignTo(config->zStackSize, stackAlignment))
       error("stack size must be " + Twine(stackAlignment) + "-byte aligned");
     log("mem: stack size  = " + Twine(config->zStackSize));
     log("mem: stack base  = " + Twine(memoryPtr));
     memoryPtr += config->zStackSize;
     auto *sp = cast<DefinedGlobal>(WasmSym::stackPointer);