add MI_PADDING flag to cmake to supress use of padding in debug mode

CMakeLists.txt

@@ -14,6 +14,7 @@ option(MI_OSX_ZONE          "Use malloc zone to override standard malloc on macO
 option(MI_LOCAL_DYNAMIC_TLS "Use slightly slower, dlopen-compatible TLS mechanism (Unix)" OFF)
 option(MI_BUILD_TESTS       "Build test executables" ON)
 option(MI_CHECK_FULL        "Use full internal invariant checking in DEBUG mode (deprecated, use MI_DEBUG_FULL instead)" OFF)
+option(MI_PADDING           "Enable padding to detect heap block overflow (only in debug mode)" ON)
 
 include("cmake/mimalloc-config-version.cmake")
 
@@ -99,6 +100,11 @@ if(MI_DEBUG_FULL MATCHES "ON")
   list(APPEND mi_defines MI_DEBUG=3)   # full invariant checking
 endif()
 
+if(MI_PADDING MATCHES "OFF")
+  message(STATUS "Disable padding of heap blocks in debug mode (MI_PADDING=OFF)")
+  list(APPEND mi_defines MI_PADDING=0)
+endif()
+
 if(MI_USE_CXX MATCHES "ON")
   message(STATUS "Use the C++ compiler to compile (MI_USE_CXX=ON)")
   set_source_files_properties(${mi_sources} PROPERTIES LANGUAGE CXX )

include/mimalloc-types.h

@@ -57,7 +57,7 @@ terms of the MIT license. A copy of the license can be found in the file
 
 // Encoded free lists allow detection of corrupted free lists
 // and can detect buffer overflows, modify after free, and double `free`s.
-#if (MI_SECURE>=3 || MI_DEBUG>=1 || defined(MI_PADDING))
+#if (MI_SECURE>=3 || MI_DEBUG>=1 || MI_PADDING > 0)
 #define MI_ENCODE_FREELIST  1
 #endif
 
@@ -303,7 +303,7 @@ typedef struct mi_random_cxt_s {
 
 
 // In debug mode there is a padding stucture at the end of the blocks to check for buffer overflows
-#if defined(MI_PADDING)
+#if (MI_PADDING)
 typedef struct mi_padding_s {
   uint32_t canary; // encoded block value to check validity of the padding (in case of overflow)
   uint32_t delta;  // padding bytes before the block. (mi_usable_size(p) - delta == exact allocated bytes)

src/alloc.c

@@ -44,7 +44,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
     mi_heap_stat_increase(heap, normal[bin], 1);
   }
 #endif
-#if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
+#if (MI_PADDING > 0) && defined(MI_ENCODE_FREELIST)
   mi_padding_t* const padding = (mi_padding_t*)((uint8_t*)block + mi_page_usable_block_size(page));
   ptrdiff_t delta = ((uint8_t*)padding - (uint8_t*)block - (size - MI_PADDING_SIZE));
   mi_assert_internal(delta >= 0 && mi_page_usable_block_size(page) >= (size - MI_PADDING_SIZE + delta));
@@ -203,7 +203,7 @@ static inline bool mi_check_is_double_free(const mi_page_t* page, const mi_block
 // Check for heap block overflow by setting up padding at the end of the block
 // ---------------------------------------------------------------------------
 
-#if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
+#if (MI_PADDING>0) && defined(MI_ENCODE_FREELIST)
 static bool mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* delta, size_t* bsize) {
   *bsize = mi_page_usable_block_size(page);
   const mi_padding_t* const padding = (mi_padding_t*)((uint8_t*)block + *bsize);

src/init.c

@@ -32,9 +32,9 @@ const mi_page_t _mi_page_empty = {
 
 #define MI_PAGE_EMPTY() ((mi_page_t*)&_mi_page_empty)
 
-#if defined(MI_PADDING) && (MI_INTPTR_SIZE >= 8)
+#if (MI_PADDING>0) && (MI_INTPTR_SIZE >= 8)
 #define MI_SMALL_PAGES_EMPTY  { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY(), MI_PAGE_EMPTY() }
-#elif defined(MI_PADDING)
+#elif (MI_PADDING>0)
 #define MI_SMALL_PAGES_EMPTY  { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY(), MI_PAGE_EMPTY(), MI_PAGE_EMPTY() }
 #else
 #define MI_SMALL_PAGES_EMPTY  { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY() }

test/main-override-static.c

@@ -19,7 +19,7 @@ int main() {
   // double_free1();
   // double_free2();
   // corrupt_free();
-  // block_overflow1();
+  block_overflow1();
 
   void* p1 = malloc(78);
   void* p2 = malloc(24);

test/main-override.cpp

@@ -29,12 +29,10 @@ void various_tests();
 int main() {
   mi_stats_reset();  // ignore earlier allocations
   heap_thread_free_large();
-  /*
   heap_no_delete();  
   heap_late_free();  
   padding_shrink();  
   various_tests();
-  */
   mi_stats_print(NULL);
   return 0;
 }