[lld][WebAssembly] Add --no-growable-memory

lld/docs/WebAssembly.rst

@@ -135,6 +135,10 @@ WebAssembly-specific options:
 
   Maximum size of the linear memory. Default: unlimited.
 
+.. option:: --no-growable-memory
+
+  Set maximum size of the linear memory to its initial size, disallowing memory growth.
+
 By default the function table is neither imported nor exported, but defined
 for internal use only.
 

lld/test/wasm/data-layout.s

@@ -103,6 +103,22 @@ local_struct_internal_ptr:
 # CHECK-MAX-NEXT:         Minimum:         0x2
 # CHECK-MAX-NEXT:         Maximum:         0x2
 
+# RUN: wasm-ld --no-entry --initial-memory=327680 --no-growable-memory \
+# RUN:     -o %t_max.wasm %t.hello32.o
+# RUN: obj2yaml %t_max.wasm | FileCheck %s -check-prefix=CHECK-NO-GROWTH
+
+# CHECK-NO-GROWTH:        - Type:            MEMORY
+# CHECK-NO-GROWTH-NEXT:     Memories:
+# CHECK-NO-GROWTH-NEXT:       - Flags:           [ HAS_MAX ]
+# CHECK-NO-GROWTH-NEXT:         Minimum:         0x5
+# CHECK-NO-GROWTH-NEXT:         Maximum:         0x5
+
+# RUN: not wasm-ld --max-memory=262144 --no-growable-memory \
+# RUN:     --no-entry -o %t_max.wasm %t.hello32.o 2>&1 \
+# RUN: | FileCheck %s --check-prefix CHECK-NO-GROWTH-COMPAT-ERROR
+
+# CHECK-NO-GROWTH-COMPAT-ERROR: --max-memory is incompatible with --no-growable-memory
+
 # RUN: wasm-ld -no-gc-sections --allow-undefined --no-entry --shared-memory \
 # RUN:     --features=atomics,bulk-memory --initial-memory=131072 \
 # RUN:     --max-memory=131072 -o %t_max.wasm %t32.o %t.hello32.o

lld/wasm/Config.h

@@ -78,6 +78,7 @@ struct Configuration {
   uint64_t initialHeap;
   uint64_t initialMemory;
   uint64_t maxMemory;
+  bool noGrowableMemory;
   // The table offset at which to place function addresses.  We reserve zero
   // for the null function pointer.  This gets set to 1 for executables and 0
   // for shared libraries (since they always added to a dynamic offset at

lld/wasm/Driver.cpp

@@ -542,9 +542,15 @@ static void readConfigs(opt::InputArgList &args) {
   config->initialHeap = args::getInteger(args, OPT_initial_heap, 0);
   config->initialMemory = args::getInteger(args, OPT_initial_memory, 0);
   config->maxMemory = args::getInteger(args, OPT_max_memory, 0);
+  config->noGrowableMemory = args.hasArg(OPT_no_growable_memory);
   config->zStackSize =
       args::getZOptionValue(args, OPT_z, "stack-size", WasmPageSize);
 
+  if (config->maxMemory != 0 && config->noGrowableMemory) {
+    // Erroring out here is simpler than defining precedence rules.
+    error("--max-memory is incompatible with --no-growable-memory");
+  }
+
   // Default value of exportDynamic depends on `-shared`
   config->exportDynamic =
       args.hasFlag(OPT_export_dynamic, OPT_no_export_dynamic, config->shared);

lld/wasm/Options.td

@@ -230,6 +230,9 @@ def initial_memory: JJ<"initial-memory=">,
 def max_memory: JJ<"max-memory=">,
   HelpText<"Maximum size of the linear memory">;
 
+def no_growable_memory: FF<"no-growable-memory">,
+  HelpText<"Set maximum size of the linear memory to its initial size">;
+
 def no_entry: FF<"no-entry">,
   HelpText<"Do not output any entry point">;
 

lld/wasm/Writer.cpp

@@ -473,6 +473,7 @@ void Writer::layoutMemory() {
     WasmSym::heapEnd->setVA(memoryPtr);
   }
 
+  uint64_t maxMemory = 0;
   if (config->maxMemory != 0) {
     if (config->maxMemory != alignTo(config->maxMemory, WasmPageSize))
       error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
@@ -481,20 +482,23 @@ void Writer::layoutMemory() {
     if (config->maxMemory > maxMemorySetting)
       error("maximum memory too large, cannot be greater than " +
             Twine(maxMemorySetting));
+
+    maxMemory = config->maxMemory;
+  } else if (config->noGrowableMemory) {
+    maxMemory = memoryPtr;
   }
 
-  // Check max if explicitly supplied or required by shared memory
-  if (config->maxMemory != 0 || config->sharedMemory) {
-    uint64_t max = config->maxMemory;
-    if (max == 0) {
-      // If no maxMemory config was supplied but we are building with
-      // shared memory, we need to pick a sensible upper limit.
-      if (ctx.isPic)
-        max = maxMemorySetting;
-      else
-        max = memoryPtr;
-    }
-    out.memorySec->maxMemoryPages = max / WasmPageSize;
+  // If no maxMemory config was supplied but we are building with
+  // shared memory, we need to pick a sensible upper limit.
+  if (config->sharedMemory && maxMemory == 0) {
+    if (ctx.isPic)
+      maxMemory = maxMemorySetting;
+    else
+      maxMemory = memoryPtr;
+  }
+
+  if (maxMemory != 0) {
+    out.memorySec->maxMemoryPages = maxMemory / WasmPageSize;
     log("mem: max pages   = " + Twine(out.memorySec->maxMemoryPages));
   }
 }