Reduce default stack size from 5Mb to 64Kb

See ChangeLog.md for rationale.

Author: sbc100

ChangeLog.md

@@ -31,6 +31,17 @@ See docs/process.md for more on how version tagging works.
   overflow will trap rather corrupting global data first).  This should not
   be a user-visible change (unless your program does something very odd such
   depending on the specific location of stack data in memory). (#18154)
+- Default value for `STACK_SIZE` (the size of the wasm shadow stack) was reduced
+  from 5Mb to 64Mb.  Project that use more that 64Kb of stack will now have to
+  start specifying `-sSTACK_SIZE` at link time.  To aid in debugging, as of
+  #18154, we now also place the stack first in memory in debug builds so that
+  overflows will be immediately detected, and result in runtime errors.
+  This change brings emscripten into line with wasm-ld and wasi-sdk defaults.
+  In general, WebAssembly stack usage should be lower than on other platforms
+  since a lot of state normally stores on the stack is hidden from the runtime
+  and doesn't use the shadow stack at all.
+  The default for `DEFAULT_PTHREAD_STACK_SIZE` was also reduced from 2Mb to 64Kb
+  to match.
 
 3.1.25 - 11/08/22
 -----------------

src/library.js

@@ -3142,12 +3142,14 @@ mergeInto(LibraryManager.library, {
 #if STACK_OVERFLOW_CHECK
   // Used by wasm-emscripten-finalize to implement STACK_OVERFLOW_CHECK
   __handle_stack_overflow__sig: 'vp',
-  __handle_stack_overflow__deps: ['emscripten_stack_get_base'],
+  __handle_stack_overflow__deps: ['emscripten_stack_get_base', 'emscripten_stack_get_end', '$ptrToString'],
   __handle_stack_overflow: function(requested) {
     requested = requested >>> 0;
+    var base = _emscripten_stack_get_base();
+    var end = _emscripten_stack_get_end();
     abort('stack overflow (Attempt to set SP to ' + ptrToString(requested) +
-          ', with stack limits [' + ptrToString(_emscripten_stack_get_end()) +
-          ' - ' + ptrToString(_emscripten_stack_get_base()) + '])');
+          ', with stack limits [' + ptrToString(end) + ' - ' + ptrToString(base) +
+          ']). If you require more stack space build with -sSTACK_SIZE=<bytes>');
   },
 #endif
 

src/settings.js

@@ -110,7 +110,7 @@ var MEM_INIT_METHOD = false;
 // assertions are on, we will assert on not exceeding this, otherwise,
 // it will fail silently.
 // [link]
-var STACK_SIZE = 5*1024*1024;
+var STACK_SIZE = 64*1024;
 
 // What malloc()/free() to use, out of
 //  * dlmalloc - a powerful general-purpose malloc
@@ -1592,7 +1592,7 @@ var PTHREAD_POOL_DELAY_LOAD = false;
 // those that have their addresses taken, or ones that are too large to fit as
 // local vars in wasm code.
 // [link]
-var DEFAULT_PTHREAD_STACK_SIZE = 2*1024*1024;
+var DEFAULT_PTHREAD_STACK_SIZE = 64*1024;
 
 // True when building with --threadprofiler
 // [link]

test/core/test_emmalloc_memory_statistics.cpp

@@ -2,30 +2,29 @@
 #include <emscripten/emmalloc.h>
 
 template<typename T>
-T round_to_4k(T val) {
-  return (T)(((size_t)val + 4095) & ~4095);
+T round_to_4k(T val){
+	return (T)(((size_t)val + 4095) & ~4095);
 }
 
-int main() {
-  void *ptr = malloc(32*1024*1024);
-  void *ptr2 = malloc(4*1024*1024);
-  void *ptr3 = malloc(64*1024*1024);
-  void *ptr4 = malloc(16*1024);
-  void *ptr5 = malloc(2*1024*1024);
-  printf("%ld\n", (long)(ptr && ptr2 && ptr3 && ptr4 && ptr5));
-  free(ptr2);
-  free(ptr4);
-  printf("validate_memory_regions: %d\n", emmalloc_validate_memory_regions());
-  printf("dynamic_heap_size: %zu\n", emmalloc_dynamic_heap_size());
-  printf("free_dynamic_memory: %zu\n", emmalloc_free_dynamic_memory());
-  size_t numFreeMemoryRegions = 0;
-  size_t freeMemorySizeMap[32];
-  numFreeMemoryRegions = emmalloc_compute_free_dynamic_memory_fragmentation_map(freeMemorySizeMap);
-  printf("numFreeMemoryRegions: %zu\n", numFreeMemoryRegions);
-  for (int i = 0; i < 32; ++i) {
-    printf("%zu ", freeMemorySizeMap[i]);
-  }
-  printf("\n");
-  printf("unclaimed_heap_memory: %zu\n", round_to_4k(emmalloc_unclaimed_heap_memory()));
-  return 0;
+int main()
+{
+	void *ptr = malloc(32*1024*1024);
+	void *ptr2 = malloc(4*1024*1024);
+	void *ptr3 = malloc(64*1024*1024);
+	void *ptr4 = malloc(16*1024);
+	void *ptr5 = malloc(2*1024*1024);
+	printf("valid allocs: %d\n", (int)(ptr && ptr2 && ptr3 && ptr4 && ptr5));
+	free(ptr2);
+	free(ptr4);
+	printf("emmalloc_validate_memory_regions: %d\n", emmalloc_validate_memory_regions());
+	printf("emmalloc_dynamic_heap_size      : %zu\n", emmalloc_dynamic_heap_size());
+	printf("emmalloc_free_dynamic_memory    : %zu\n", emmalloc_free_dynamic_memory());
+	size_t numFreeMemoryRegions = 0;
+	size_t freeMemorySizeMap[32];
+	numFreeMemoryRegions = emmalloc_compute_free_dynamic_memory_fragmentation_map(freeMemorySizeMap);
+	printf("numFreeMemoryRegions: %zu\n", numFreeMemoryRegions);
+	for(int i = 0; i < 32; ++i)
+		printf("%zu ", freeMemorySizeMap[i]);
+	printf("\n");
+	printf("emmalloc_unclaimed_heap_memory  : %zu\n", round_to_4k(emmalloc_unclaimed_heap_memory()));
 }

test/core/test_emmalloc_memory_statistics.out

@@ -1,7 +1,7 @@
-1
-validate_memory_regions: 0
-dynamic_heap_size: 106971424
-free_dynamic_memory: 4210892
+valid allocs: 1
+emmalloc_validate_memory_regions: 0
+emmalloc_dynamic_heap_size      : 106971424
+emmalloc_free_dynamic_memory    : 4210892
 numFreeMemoryRegions: 3
 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 
-unclaimed_heap_memory: 21999616
+emmalloc_unclaimed_heap_memory  : 27176960

test/core/test_memcpy3.c

@@ -26,7 +26,7 @@
 int main() {
   #define RUN(type) \
   { \
-    type buffer[TOTAL]; \
+    static type buffer[TOTAL]; \
     volatile int seed = 123; \
     TEST(1, type); \
     TEST(2, type); \

test/core/test_memorygrowth_geometric_step.out

@@ -1,2 +1,2 @@
 Heap size before allocation: 16777216
-Ptr: 1, value: 16843009, Heap size now: 101777408 (increase: 85000192 bytes)
+Ptr: 1, value: 16843009, Heap size now: 96600064 (increase: 79822848 bytes)

test/core/test_memset.c

@@ -26,7 +26,7 @@
 int main() {
   #define RUN(type) \
   { \
-    type buffer[TOTAL]; \
+    static type buffer[TOTAL]; \
     volatile int seed = 123; \
     TEST(1, type); \
     TEST(2, type); \

test/fs/test_mmap.c

@@ -180,11 +180,12 @@ void test_mmap_shared_with_offset() {
     assert(fd >= 0);
     size_t offset = sysconf(_SC_PAGE_SIZE) * 2;
 
-    char buffer[offset + 33];
-    memset(buffer, 0, offset + 33);
-    fread(buffer, 1, offset + 32, fd);
+    char buffer[33];
+    memset(buffer, 0, 33);
+    fseek(fd, offset, SEEK_SET);
+    fread(buffer, 1, 32, fd);
     // expect text written from mmap operation to appear at offset in the file
-    printf("yolo/sharedoffset.txt content=%s %zu\n", buffer + offset, offset);
+    printf("yolo/sharedoffset.txt content=%s %zu\n", buffer, offset);
     fclose(fd);
   }
 }

test/test_other.py

@@ -2620,6 +2620,8 @@ def test_embind(self, extra_args):
          '--pre-js', test_file('embind/test.pre.js'),
          '--post-js', test_file('embind/test.post.js'),
          '-sWASM_ASYNC_COMPILATION=0',
+         # The default stack size is not enough for these tests.
+         '-sTOTAL_STACK=2Mb',
          '-sIN_TEST_HARNESS'] + args)
 
       if '-sDYNAMIC_EXECUTION=0' in args:
@@ -5818,7 +5820,7 @@ def test_massive_alloc(self, wasm):
     # just care about message regarding allocating over 1GB of memory
     output = self.run_js('a.out.js')
     if not wasm:
-      self.assertContained('Warning: Enlarging memory arrays, this is not fast! 16777216,1473314816\n', output)
+      self.assertContained('Warning: Enlarging memory arrays, this is not fast! 16777216,1468137472\n', output)
 
   def test_failing_alloc(self):
     for pre_fail, post_fail, opts in [