3 files changed, 29 insertions, 16 deletions

diff --git a/ext/wasm/common/emscripten.css b/ext/wasm/common/emscripten.css
index 7e3dc811d..d8f82c73b 100644
--- a/ext/wasm/common/emscripten.css
+++ b/ext/wasm/common/emscripten.css
@@ -1,4 +1,4 @@
-/* emcscript-related styling, used during the module load/intialization processes... */
+/* emscripten-related styling, used during the module load/intialization processes... */
 .emscripten { padding-right: 0; margin-left: auto; margin-right: auto; display: block; }
 div.emscripten { text-align: center; }
 div.emscripten_border { border: 1px solid black; }
diff --git a/ext/wasm/common/testing.css b/ext/wasm/common/testing.css
index 9438b330c..fb44f1d61 100644
--- a/ext/wasm/common/testing.css
+++ b/ext/wasm/common/testing.css
@@ -61,3 +61,9 @@ span.labeled-input {
   flex-direction: column-reverse;
 }
 label[for] { cursor: pointer }
+
+h1 {
+  border-radius: 0.25em;
+  padding: 0.15em 0.25em;
+}
+h1:first-of-type {margin: 0 0 0.5em 0;}
diff --git a/ext/wasm/common/whwasmutil.js b/ext/wasm/common/whwasmutil.js
index 8cb483324..9bce82f1a 100644
--- a/ext/wasm/common/whwasmutil.js
+++ b/ext/wasm/common/whwasmutil.js
@@ -725,11 +725,12 @@ self.WhWasmUtilInstaller = function(target){
      Expects ptr to be a pointer into the WASM heap memory which
      refers to a NUL-terminated C-style string encoded as UTF-8.
      Returns the length, in bytes, of the string, as for `strlen(3)`.
-     As a special case, if !ptr then it it returns `null`. Throws if
-     ptr is out of range for target.heap8u().
+     As a special case, if !ptr or if it's not a pointer then it
+     returns `null`. Throws if ptr is out of range for
+     target.heap8u().
   */
   target.cstrlen = function(ptr){
-    if(!ptr) return null;
+    if(!ptr || !target.isPtr(ptr)) return null;
     const h = heapWrappers().HEAP8U;
     let pos = ptr;
     for( ; h[pos] !== 0; ++pos ){}
@@ -753,7 +754,7 @@ self.WhWasmUtilInstaller = function(target){
      refers to a NUL-terminated C-style string encoded as UTF-8. This
      function counts its byte length using cstrlen() then returns a
      JS-format string representing its contents. As a special case, if
-     ptr is falsy, `null` is returned.
+     ptr is falsy or not a pointer, `null` is returned.
   */
   target.cstringToJs = function(ptr){
     const n = target.cstrlen(ptr);
@@ -1081,10 +1082,9 @@ self.WhWasmUtilInstaller = function(target){
 
   // impl for allocMainArgv() and scopedAllocMainArgv().
   const __allocMainArgv = function(isScoped, list){
-    if(!list.length) toss("Cannot allocate empty array.");
     const pList = target[
       isScoped ? 'scopedAlloc' : 'alloc'
-    ](list.length * target.ptrSizeof);
+    ]((list.length + 1) * target.ptrSizeof);
     let i = 0;
     list.forEach((e)=>{
       target.setPtrValue(pList + (target.ptrSizeof * i++),
@@ -1092,26 +1092,33 @@ self.WhWasmUtilInstaller = function(target){
                            isScoped ? 'scopedAllocCString' : 'allocCString'
                          ](""+e));
     });
+    target.setPtrValue(pList + (target.ptrSizeof * i), 0);
     return pList;
   };
 
   /**
      Creates an array, using scopedAlloc(), suitable for passing to a
      C-level main() routine. The input is a collection with a length
-     property and a forEach() method. A block of memory list.length
-     entries long is allocated and each pointer-sized block of that
-     memory is populated with a scopedAllocCString() conversion of the
-     (""+value) of each element. Returns a pointer to the start of the
-     list, suitable for passing as the 2nd argument to a C-style
-     main() function.
-
-     Throws if list.length is falsy or scopedAllocPush() is not active.
+     property and a forEach() method. A block of memory
+     (list.length+1) entries long is allocated and each pointer-sized
+     block of that memory is populated with a scopedAllocCString()
+     conversion of the (""+value) of each element, with the exception
+     that the final entry is a NULL pointer. Returns a pointer to the
+     start of the list, suitable for passing as the 2nd argument to a
+     C-style main() function.
+
+     Throws if scopedAllocPush() is not active.
+
+     Design note: the returned array is allocated with an extra NULL
+     pointer entry to accommodate certain APIs, but client code which
+     does not need that functionality should treat the returned array
+     as list.length entries long.
   */
   target.scopedAllocMainArgv = (list)=>__allocMainArgv(true, list);
 
   /**
      Identical to scopedAllocMainArgv() but uses alloc() instead of
-     scopedAllocMainArgv
+     scopedAlloc().
   */
   target.allocMainArgv = (list)=>__allocMainArgv(false, list);