fix MI_GUARDED build

ide/vs2022/mimalloc.vcxproj

@@ -116,7 +116,7 @@
       <SDLCheck>true</SDLCheck>
       <ConformanceMode>Default</ConformanceMode>
       <AdditionalIncludeDirectories>../../include</AdditionalIncludeDirectories>
-      <PreprocessorDefinitions>MI_DEBUG=3;MI_GUARDED=0;%(PreprocessorDefinitions);</PreprocessorDefinitions>
+      <PreprocessorDefinitions>MI_DEBUG=3;%(PreprocessorDefinitions);</PreprocessorDefinitions>
       <CompileAs>CompileAsCpp</CompileAs>
       <SupportJustMyCode>false</SupportJustMyCode>
       <LanguageStandard>stdcpp20</LanguageStandard>

src/alloc.c

@@ -628,6 +628,9 @@ static void* mi_block_ptr_set_guarded(mi_block_t* block, size_t obj_size) {
     return NULL;
   }
   uint8_t* guard_page = (uint8_t*)block + block_size - os_page_size;
+  // note: the alignment of the guard page relies on blocks being os_page_size aligned which
+  // is ensured in `mi_arena_page_alloc_fresh`.
+  mi_assert_internal(_mi_is_aligned(block, os_page_size));
   mi_assert_internal(_mi_is_aligned(guard_page, os_page_size));
   if (!page->memid.is_pinned && _mi_is_aligned(guard_page, os_page_size)) {
     _mi_os_protect(guard_page, os_page_size);

src/arena.c

@@ -624,7 +624,23 @@ static mi_page_t* mi_arena_page_alloc_fresh(size_t slice_count, size_t block_siz
   if (MI_PAGE_INFO_SIZE < _mi_align_up(sizeof(*page), MI_PAGE_MIN_BLOCK_ALIGN)) {
     _mi_error_message(EFAULT, "fatal internal error: MI_PAGE_INFO_SIZE is too small.\n");
   };
-  const size_t block_start = (os_align ? MI_PAGE_ALIGN : MI_PAGE_INFO_SIZE);
+  size_t block_start;
+  #if MI_GUARDED
+  // in a guarded build, we aling pages with blocks a multiple of an OS page size, to the OS page size
+  // this ensures that all blocks in such pages are OS page size aligned (which is needed for the guard pages)
+  const size_t os_page_size = _mi_os_page_size();
+  mi_assert_internal(MI_PAGE_ALIGN >= os_page_size);
+  if (block_size % os_page_size == 0) {
+    block_start = _mi_align_up(MI_PAGE_INFO_SIZE, os_page_size);
+  }
+  else
+  #endif
+  if (os_align) {
+    block_start = MI_PAGE_ALIGN;
+  }
+  else {
+    block_start = MI_PAGE_INFO_SIZE;
+  }
   const size_t reserved    = (os_align ? 1 : (mi_size_of_slices(slice_count) - block_start) / block_size);
   mi_assert_internal(reserved > 0 && reserved <= UINT16_MAX);
   page->reserved = (uint16_t)reserved;

src/init.c

@@ -180,7 +180,7 @@ mi_decl_export void mi_heap_guarded_set_sample_rate(mi_heap_t* heap, size_t samp
   if (heap->guarded_sample_rate >= 1) {
     heap->guarded_sample_seed = heap->guarded_sample_seed % heap->guarded_sample_rate;
   }
-  heap->guarded_sample_count = heap->guarded_sample_seed;  // count down samples
+  heap->guarded_sample_count = 1 + heap->guarded_sample_seed;  // count down samples
 }
 
 mi_decl_export void mi_heap_guarded_set_size_bound(mi_heap_t* heap, size_t min, size_t max) {

src/libc.c

@@ -84,8 +84,8 @@ bool _mi_getenv(const char* name, char* result, size_t result_size) {
 // This is mostly to avoid calling these when libc is not yet
 // initialized (and to reduce dependencies)
 //
-// format:      d i, p x u, s
-// prec:        z l ll L
+// format:      d i, p, x, u, s
+// type:        z l ll L
 // width:       10
 // align-left:  -
 // fill:        0

test/main-override-static.c

@@ -233,8 +233,8 @@ static void test_heap_walk(void) {
 }
 
 static void test_canary_leak(void) {
-  char* p = mi_mallocn_tp(char, 23);
-  for (int i = 0; i < 23; i++) {
+  char* p = mi_mallocn_tp(char, 22);
+  for (int i = 0; i < 22; i++) {
     p[i] = '0'+i;
   }
   puts(p);

test/test-stress.c

@@ -42,7 +42,7 @@ static int SCALE   = 10;
 static int ITER    = 10;
 #elif 0
 static int THREADS = 4;
-static int SCALE   = 100;
+static int SCALE   = 10;
 static int ITER    = 10;
 #define ALLOW_LARGE false
 #elif 0