[WebAssembly] "atomics" feature requires shared memory

Summary:
Makes it a linker error if the "atomics" feature is used but the user
does not opt in to shared memory or if "atomics" is disallowed but the
user does opt in to shared memory. Also check that an appropriate max
memory size is supplied if shared memory is used.

Reviewers: sbc100, aheejin

Subscribers: dschuff, jgravelle-google, sunfish, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59281

llvm-svn: 357310

1 files changed, 11 insertions, 3 deletions

diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index 63e33d69962..50dc76f8e41 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -169,7 +169,7 @@ void Writer::createImportSection() {
     Import.Kind = WASM_EXTERNAL_MEMORY;
     Import.Memory.Flags = 0;
     Import.Memory.Initial = NumMemoryPages;
-    if (MaxMemoryPages != 0) {
+    if (MaxMemoryPages != 0 || Config->SharedMemory) {
       Import.Memory.Flags |= WASM_LIMITS_FLAG_HAS_MAX;
       Import.Memory.Maximum = MaxMemoryPages;
     }
@@ -257,7 +257,7 @@ void Writer::createMemorySection() {
   SyntheticSection *Section = createSyntheticSection(WASM_SEC_MEMORY);
   raw_ostream &OS = Section->getStream();
 
-  bool HasMax = MaxMemoryPages != 0;
+  bool HasMax = MaxMemoryPages != 0 || Config->SharedMemory;
   writeUleb128(OS, 1, "memory count");
   unsigned Flags = 0;
   if (HasMax)
@@ -831,7 +831,8 @@ void Writer::layoutMemory() {
   NumMemoryPages = alignTo(MemoryPtr, WasmPageSize) / WasmPageSize;
   log("mem: total pages = " + Twine(NumMemoryPages));
 
-  if (Config->MaxMemory != 0) {
+  // Check max if explicitly supplied or required by shared memory
+  if (Config->MaxMemory != 0 || Config->SharedMemory) {
     if (Config->MaxMemory != alignTo(Config->MaxMemory, WasmPageSize))
       error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
     if (MemoryPtr > Config->MaxMemory)
@@ -927,9 +928,16 @@ void Writer::calculateTargetFeatures() {
   if (InferFeatures)
     TargetFeatures.insert(Used.begin(), Used.end());
 
+  if (TargetFeatures.count("atomics") && !Config->SharedMemory)
+    error("'atomics' feature is used, so --shared-memory must be used");
+
   if (!Config->CheckFeatures)
     return;
 
+  if (Disallowed.count("atomics") && Config->SharedMemory)
+    error(
+        "'atomics' feature is disallowed, so --shared-memory must not be used");
+
   // Validate that used features are allowed in output
   if (!InferFeatures) {
     for (auto &Feature : Used) {