[lld][WebAssembly] Fix malformed output with -pie + --shared-memory

The conditional guarding createInitMemoryFunction was incorrect and
didn't match that guarding the creation of the associated symbol.

Rather that reproduce the same conditions in multiple places we can
simply use the presence of the associated symbol.

Also, add an assertion that would have caught this bug.

Also, add a new test for this flag combination.

This is part of an ongoing effort to enable dynamic linking with
threads in emscripten.

See https://github.com/emscripten-core/emscripten/issues/3494

Differential Revision: https://reviews.llvm.org/D92520

lld/test/wasm/data-segments.ll

@@ -13,6 +13,10 @@
 ; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.wasm
 ; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefixes PASSIVE
 
+; Also test in combination with PIC/pie
+; RUN: llc -filetype=obj -relocation-model=pic %s -o %t.atomics.bulk-mem.pic.o -mattr=+atomics,+bulk-memory,+mutable-globals
+; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
+
 target triple = "wasm32-unknown-unknown"
 
 @a = hidden global [6 x i8] c"hello\00", align 1

lld/wasm/MarkLive.cpp

@@ -96,15 +96,13 @@ void MarkLive::run() {
     if (sym->isNoStrip() || sym->isExported())
       enqueue(sym);
 
-  // If we'll be calling the user's `__wasm_call_dtors` function, mark it live.
-  if (Symbol *callDtors = WasmSym::callDtors)
-    enqueue(callDtors);
+  if (WasmSym::callDtors)
+    enqueue(WasmSym::callDtors);
 
-  // In Emscripten-style PIC, `__wasm_call_ctors` calls `__wasm_apply_relocs`.
-  if (config->isPic)
+  if (WasmSym::applyRelocs)
     enqueue(WasmSym::applyRelocs);
 
-  if (config->sharedMemory && !config->shared)
+  if (WasmSym::initMemory)
     enqueue(WasmSym::initMemory);
 
   // Enqueue constructors in objects explicitly live from the command-line.

lld/wasm/OutputSections.cpp

@@ -90,6 +90,8 @@ void CodeSection::finalizeContents() {
     func->outputSec = this;
     func->outputOffset = bodySize;
     func->calculateSize();
+    // All functions should have a non-empty body at this point
+    assert(func->getSize());
     bodySize += func->getSize();
   }
 

lld/wasm/Writer.cpp

@@ -1214,11 +1214,12 @@ void Writer::run() {
   calculateInitFunctions();
 
   if (!config->relocatable) {
-    // Create linker synthesized functions
-    if (config->isPic)
+    if (WasmSym::applyRelocs)
       createApplyRelocationsFunction();
-    else if (config->sharedMemory)
+    if (WasmSym::initMemory)
       createInitMemoryFunction();
+
+    // Create linker synthesized functions
     createCallCtorsFunction();
 
     // Create export wrappers for commands if needed.