[WebAssembly] Set __tls_align to 1 when there is no TLS

[quantum]

Summary

We want the tool conventions to state that __tls_align will be a power of 2.
It makes sense to not have an exception for when there is no TLS.

[tlively]

lld/test/wasm/no-tls.test

1 ↗

(On Diff #211392)

Why not have the input in this file?

lld/wasm/Driver.cpp

532 ↗

(On Diff #211392)

May as well update these calls to explicitly pass zero as well, and make it nonoptional. I assume there are no other calls to this function elsewhere?

[quantum]

Switched to not using default arguments

[quantum]

lld/test/wasm/no-tls.test

1 ↗

(On Diff #211392)

I did a test like this before and @sbc100 asked for it to be made into a .test file that uses one of the existing input files.

lld/wasm/Driver.cpp

532 ↗

(On Diff #211392)

Done.

[tlively]

lld/test/wasm/no-tls.test

1 ↗

(On Diff #211392)

Please add a comment saying what this is meant to be testing. I don't think it will be clear just from the name and contents for future readers.

[quantum]

Add a comment to explain what the test is testing.

lld/trunk/test/wasm/no-tls.test

+; Testing that __tls_size and __tls_align are correctly emitted when there are
+; no thread_local variables.
+
+RUN: llc -mattr=+bulk-memory -filetype=obj %p/Inputs/start.ll -o %t.o
+
+RUN: wasm-ld -no-gc-sections --shared-memory --max-memory=131072 --allow-undefined -o %t.wasm %t.o
+RUN: obj2yaml %t.wasm | FileCheck %s
+CHECK:       - Type:            GLOBAL
+CHECK-NEXT:    Globals:
+
+; __stack_pointer
+CHECK-NEXT:      - Index:           0
+CHECK-NEXT:        Type:            I32
+CHECK-NEXT:        Mutable:         true
+CHECK-NEXT:        InitExpr:
+CHECK-NEXT:          Opcode:          I32_CONST
+CHECK-NEXT:          Value:           66560
+
+; __tls_base
+CHECK-NEXT:      - Index:           1
+CHECK-NEXT:        Type:            I32
+CHECK-NEXT:        Mutable:         true
+CHECK-NEXT:        InitExpr:
+CHECK-NEXT:          Opcode:          I32_CONST
+CHECK-NEXT:          Value:           0
+
+; __tls_size
+CHECK-NEXT:      - Index:           2
+CHECK-NEXT:        Type:            I32
+CHECK-NEXT:        Mutable:         false
+CHECK-NEXT:        InitExpr:
+CHECK-NEXT:          Opcode:          I32_CONST
+CHECK-NEXT:          Value:           0
+
+; __tls_align
+CHECK-NEXT:      - Index:           3
+CHECK-NEXT:        Type:            I32
+CHECK-NEXT:        Mutable:         false
+CHECK-NEXT:        InitExpr:
+CHECK-NEXT:          Opcode:          I32_CONST
+CHECK-NEXT:          Value:           1

lld/trunk/wasm/Driver.cpp

auto *sym =
       cast<UndefinedGlobal>(symtab->addUndefinedGlobal(name, name,
                                                        defaultModule, 0,
                                                        nullptr, type));
   config->allowUndefinedSymbols.insert(sym->getName());
   sym->isUsedInRegularObj = true;
   return sym;
 }
 
-static GlobalSymbol *createGlobalVariable(StringRef name, bool isMutable) {
+static GlobalSymbol *createGlobalVariable(StringRef name, bool isMutable,
+                                          int value) {
   llvm::wasm::WasmGlobal wasmGlobal;
   wasmGlobal.Type = {WASM_TYPE_I32, isMutable};
-  wasmGlobal.InitExpr.Value.Int32 = 0;
+  wasmGlobal.InitExpr.Value.Int32 = value;
   wasmGlobal.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
   wasmGlobal.SymbolName = name;
   return symtab->addSyntheticGlobal(name, WASM_SYMBOL_VISIBILITY_HIDDEN,
                                     make<InputGlobal>(wasmGlobal, nullptr));
 }
 
 // Create ABI-defined synthetic symbols
 static void createSyntheticSymbols() {
if (config->isPic) {
     // 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) {
-    WasmSym::tlsBase = createGlobalVariable("__tls_base", true);
-    WasmSym::tlsSize = createGlobalVariable("__tls_size", false);
-    WasmSym::tlsAlign = createGlobalVariable("__tls_align", false);
+    WasmSym::tlsBase = createGlobalVariable("__tls_base", true, 0);
+    WasmSym::tlsSize = createGlobalVariable("__tls_size", false, 0);
+    WasmSym::tlsAlign = createGlobalVariable("__tls_align", false, 1);
     WasmSym::initTLS = symtab->addSyntheticFunction(
         "__wasm_init_tls", WASM_SYMBOL_VISIBILITY_HIDDEN,
         make<SyntheticFunction>(i32ArgSignature, "__wasm_init_tls"));
   }
 
   WasmSym::dsoHandle = symtab->addSyntheticDataSymbol(
       "__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
 }