check for segfaults in SAFE_HEAP

2 files changed, 6 insertions, 2 deletions

diff --git a/src/preamble.js b/src/preamble.js
index a8f19d64..bbb9d684 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -24,6 +24,8 @@ var ACCEPTABLE_SAFE_HEAP_ERRORS = 0;
 function SAFE_HEAP_ACCESS(dest, type, store, ignore) {
   //if (dest === A_NUMBER) Module.print ([dest, type, store] + ' ' + new Error().stack); // Something like this may be useful, in debugging
 
+  assert(dest >= STACK_ROOT, 'segmentation fault: null pointer, or below normal memory');
+
 #if USE_TYPED_ARRAYS
   // When using typed arrays, reads over the top of TOTAL_MEMORY will fail silently, so we must
   // correct that by growing TOTAL_MEMORY as needed. Without typed arrays, memory is a normal
@@ -643,7 +645,7 @@ var base = intArrayFromString('(null)'); // So printing %s of NULL gives '(null)
                                          // Also this ensures we leave 0 as an invalid address, 'NULL'
 STATICTOP = base.length;
 for (var i = 0; i < base.length; i++) {
-  {{{ makeSetValue(0, 'i', 'base[i]', 'i8') }}}
+  {{{ makeSetValue(0, 'i', 'base[i]', 'i8', null, null, null, 1) }}}
 }
 
 Module['HEAP'] = HEAP;
diff --git a/src/settings.js b/src/settings.js
index 9f63622d..fe532bda 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -104,7 +104,9 @@ var CATCH_EXIT_CODE = 0; // If set, causes exit() to throw an exception object w
                          // terminated with an error message.
 
 // Generated code debugging options
-var SAFE_HEAP = 0; // Check each write to the heap against a list of blocked addresses
+var SAFE_HEAP = 0; // Check each write to the heap, for example, this will give a clear
+                   // error on what would be segfaults in a native build (like deferencing
+                   // 0). See preamble.js for the actual checks performed.
                    // If equal to 2, done on a line-by-line basis according to
                    // SAFE_HEAP_LINES, checking only the specified lines.
                    // If equal to 3, checking all *but* the specified lines. Note