initial work on guarded objects

CMakeLists.txt

@@ -26,6 +26,7 @@ option(MI_BUILD_OBJECT      "Build object library" ON)
 option(MI_BUILD_TESTS       "Build test executables" ON)
 option(MI_DEBUG_TSAN        "Build with thread sanitizer (needs clang)" OFF)
 option(MI_DEBUG_UBSAN       "Build with undefined-behavior sanitizer (needs clang++)" OFF)
+option(MI_DEBUG_GUARDED     "Build with guard pages behind certain object allocations (implies MI_NO_PADDING=ON)" OFF)
 option(MI_SKIP_COLLECT_ON_EXIT "Skip collecting memory on program exit" OFF)
 option(MI_NO_PADDING        "Force no use of padding even in DEBUG mode etc." OFF)
 option(MI_INSTALL_TOPLEVEL  "Install directly into $CMAKE_INSTALL_PREFIX instead of PREFIX/lib/mimalloc-version" OFF)
@@ -199,6 +200,15 @@ if(MI_TRACK_ETW)
   endif()
 endif()
 
+if(MI_DEBUG_GUARDED)
+  message(STATUS "Compile guard pages behind certain object allocations (MI_DEBUG_GUARDED=ON)")
+  list(APPEND mi_defines MI_DEBUG_GUARDED=1)
+  if(NOT MI_NO_PADDING)
+    message(STATUS "  Disabling padding due to guard pages (MI_NO_PADDING=ON)")
+    set(MI_NO_PADDING ON)
+  endif()
+endif()
+
 if(MI_SEE_ASM)
   message(STATUS "Generate assembly listings (MI_SEE_ASM=ON)")
   list(APPEND mi_cflags -save-temps)

include/mimalloc.h

@@ -366,6 +366,8 @@ typedef enum mi_option_e {
   mi_option_disallow_arena_alloc,       // 1 = do not use arena's for allocation (except if using specific arena id's)
   mi_option_retry_on_oom,               // retry on out-of-memory for N milli seconds (=400), set to 0 to disable retries. (only on windows)
   mi_option_visit_abandoned,            // allow visiting heap blocks from abandoned threads (=0)
+  mi_option_debug_guarded_min,          // only when build with MI_DEBUG_GUARDED: minimal rounded object size for guarded objects (=0)
+  mi_option_debug_guarded_max,          // only when build with MI_DEBUG_GUARDED: maximal rounded object size for guarded objects (=0)
   _mi_option_last,
   // legacy option names
   mi_option_large_os_pages = mi_option_allow_large_os_pages,

include/mimalloc/internal.h

@@ -61,6 +61,7 @@ void       _mi_warning_message(const char* fmt, ...);
 void       _mi_verbose_message(const char* fmt, ...);
 void       _mi_trace_message(const char* fmt, ...);
 void       _mi_options_init(void);
+long       _mi_option_get_fast(mi_option_t option);
 void       _mi_error_message(int err, const char* fmt, ...);
 
 // random.c

src/options.c

@@ -99,6 +99,8 @@ static mi_option_desc_t options[_mi_option_last] =
 #else
   { 0,   UNINIT, MI_OPTION(visit_abandoned) },          
 #endif
+  { 0,   UNINIT, MI_OPTION(debug_guarded_min) },        // only when build with MI_DEBUG_GUARDED: minimal rounded object size for guarded objects (=0)     
+  { 0,   UNINIT, MI_OPTION(debug_guarded_max) },        // only when build with MI_DEBUG_GUARDED: maximal rounded object size for guarded objects (=0)  
 };
 
 static void mi_option_init(mi_option_desc_t* desc);
@@ -124,6 +126,15 @@ void _mi_options_init(void) {
   mi_max_warning_count = mi_option_get(mi_option_max_warnings);
 }
 
+long _mi_option_get_fast(mi_option_t option) {
+  mi_assert(option >= 0 && option < _mi_option_last);
+  mi_option_desc_t* desc = &options[option]; 
+  mi_assert(desc->option == option);  // index should match the option
+  //mi_assert(desc->init != UNINIT);
+  return desc->value;
+}
+  
+
 mi_decl_nodiscard long mi_option_get(mi_option_t option) {
   mi_assert(option >= 0 && option < _mi_option_last);
   if (option < 0 || option >= _mi_option_last) return 0;
@@ -508,6 +519,9 @@ static void mi_option_init(mi_option_desc_t* desc) {
       if (*end == 0) {
         desc->value = value;
         desc->init = INITIALIZED;
+        if (desc->option == mi_option_debug_guarded_min && _mi_option_get_fast(mi_option_debug_guarded_max) < value) {
+          mi_option_set(mi_option_debug_guarded_max,value);
+        }
       }
       else {
         // set `init` first to avoid recursion through _mi_warning_message on mimalloc_verbose.