capabilities to detect half/full runtime header

lib/loader/index.js

@@ -54,7 +54,8 @@ function postInstantiate(baseModule, instance) {
   var memory_fill = rawExports["memory.fill"];
   var memory_free = rawExports["memory.free"];
   var table = rawExports.table;
-  var setargc = rawExports._setargc || function() {};
+  var capabilities = rawExports[".capabilities"] || 0;
+  var setargc = rawExports[".setargc"] || function() {};
 
   // Provide views for all sorts of basic values
   var buffer, I8, U8, I16, U16, I32, U32, F32, F64, I64, U64;
@@ -245,7 +246,7 @@ exports.instantiateStreaming = instantiateStreaming;
 /** Demangles an AssemblyScript module's exports to a friendly object structure. */
 function demangle(exports, baseModule) {
   var module = baseModule ? Object.create(baseModule) : {};
-  var setargc = exports._setargc || function() {};
+  var setargc = exports[".setargc"] || function() {};
   function hasOwnProperty(elem, prop) {
     return Object.prototype.hasOwnProperty.call(elem, prop);
   }

src/compiler.ts

@@ -252,6 +252,16 @@ export const enum Feature {
   THREADS = 1 << 4 // see: https://github.com/WebAssembly/threads
 }
 
+/** Indicates module capabilities. */
+export const enum Capability {
+  /** No specific capabilities. */
+  NONE = 0,
+  /** Uses WebAssembly with 64-bit pointers. */
+  WASM64 = 1 << 0,
+  /** Garbage collector is present (full runtime header). */
+  GC = 1 << 1
+}
+
 /** Indicates the desired kind of a conversion. */
 export const enum ConversionKind {
   /** No conversion. */
@@ -440,6 +450,14 @@ export class Compiler extends DiagnosticEmitter {
     // set up gc
     if (this.needsIterateRoots) compileIterateRoots(this);
 
+    // expose module capabilities
+    var capabilities = Capability.NONE;
+    if (program.options.isWasm64) capabilities |= Capability.WASM64;
+    if (program.gcImplemented) capabilities |= Capability.GC;
+    if (capabilities != 0) {
+      module.addGlobal(CompilerSymbols.capabilities, NativeType.I32, false, module.createI32(capabilities));
+      module.addGlobalExport(CompilerSymbols.capabilities, ".capabilities");
+    }
     return module;
   }
 
@@ -5758,7 +5776,7 @@ export class Compiler extends DiagnosticEmitter {
           module.createGetLocal(0, NativeType.I32)
         )
       );
-      module.addFunctionExport(internalName, "_setargc");
+      module.addFunctionExport(internalName, ".setargc");
     }
     return internalName;
   }
@@ -8088,4 +8106,6 @@ namespace CompilerSymbols {
   export const argc = "~lib/argc";
   /** Argument count setter. Exported for use by host calls. */
   export const setargc = "~lib/setargc";
+  /** Module capabilities. Exported for evaluation by the host. */
+  export const capabilities = "~lib/capabilities";
 }

tests/compiler/exports.optimized.wat

@@ -24,7 +24,7 @@
  (export "memory" (memory $0))
  (export "table" (table $0))
  (export "add" (func $exports/add))
- (export "_setargc" (func $~lib/setargc))
+ (export ".setargc" (func $~lib/setargc))
  (export "subOpt" (func $exports/subOpt|trampoline))
  (export "math.sub" (func $exports/subOpt))
  (export "Animal.CAT" (global $exports/Animal.CAT))

tests/compiler/exports.untouched.wat

@@ -29,7 +29,7 @@
  (export "memory" (memory $0))
  (export "table" (table $0))
  (export "add" (func $exports/add))
- (export "_setargc" (func $~lib/setargc))
+ (export ".setargc" (func $~lib/setargc))
  (export "subOpt" (func $exports/subOpt|trampoline))
  (export "math.sub" (func $exports/math.sub))
  (export "Animal.CAT" (global $exports/Animal.CAT))

tests/compiler/std/runtime.optimized.wat

@@ -38,8 +38,10 @@
  (global $std/runtime/ref4 (mut i32) (i32.const 0))
  (global $std/runtime/header4 (mut i32) (i32.const 0))
  (global $std/runtime/ref5 (mut i32) (i32.const 0))
+ (global $~lib/capabilities i32 (i32.const 2))
  (export "memory" (memory $0))
  (export "table" (table $0))
+ (export ".capabilities" (global $~lib/capabilities))
  (start $start)
  (func $~lib/allocator/tlsf/Root#setSLMap (; 2 ;) (type $FUNCSIG$viii) (param $0 i32) (param $1 i32) (param $2 i32)
   local.get $1

tests/compiler/std/runtime.untouched.wat

@@ -55,8 +55,10 @@
  (global $std/runtime/header4 (mut i32) (i32.const 0))
  (global $std/runtime/ref5 (mut i32) (i32.const 0))
  (global $~lib/memory/HEAP_BASE i32 (i32.const 264))
+ (global $~lib/capabilities i32 (i32.const 2))
  (export "memory" (memory $0))
  (export "table" (table $0))
+ (export ".capabilities" (global $~lib/capabilities))
  (start $start)
  (func $start:~lib/allocator/tlsf (; 2 ;) (type $FUNCSIG$v)
   i32.const 1