gh-112529: Track if debug allocator is used as underlying allocator (#113747)

* gh-112529: Track if debug allocator is used as underlying allocator

The GC implementation for free-threaded builds will need to accurately
detect if the debug allocator is used because it affects the offset of
the Python object from the beginning of the memory allocation. The
current implementation of `_PyMem_DebugEnabled` only considers if the
debug allocator is the outer-most allocator; it doesn't handle the case
of "hooks" like tracemalloc being used on top of the debug allocator.

This change enables more accurate detection of the debug allocator by
tracking when debug hooks are enabled.

* Simplify _PyMem_DebugEnabled

4 files changed, 21 insertions, 6 deletions

diff --git a/Include/internal/pycore_pymem.h b/Include/internal/pycore_pymem.h
index c49742e..1a72d07 100644
--- a/Include/internal/pycore_pymem.h
+++ b/Include/internal/pycore_pymem.h
@@ -44,6 +44,7 @@ struct _pymem_allocators {
         debug_alloc_api_t mem;
         debug_alloc_api_t obj;
     } debug;
+    int is_debug_enabled;
     PyObjectArenaAllocator obj_arena;
 };
 
@@ -106,6 +107,8 @@ extern int _PyMem_GetAllocatorName(
    PYMEM_ALLOCATOR_NOT_SET does nothing. */
 extern int _PyMem_SetupAllocators(PyMemAllocatorName allocator);
 
+/* Is the debug allocator enabled? */
+extern int _PyMem_DebugEnabled(void);
 
 #ifdef __cplusplus
 }
diff --git a/Include/internal/pycore_pymem_init.h b/Include/internal/pycore_pymem_init.h
index 360fb92..96c49ed 100644
--- a/Include/internal/pycore_pymem_init.h
+++ b/Include/internal/pycore_pymem_init.h
@@ -70,6 +70,7 @@ extern void _PyMem_ArenaFree(void *, void *, size_t);
         PYDBGMEM_ALLOC(runtime), \
         PYDBGOBJ_ALLOC(runtime), \
     }
+# define _pymem_is_debug_enabled_INIT 1
 #else
 # define _pymem_allocators_standard_INIT(runtime) \
     { \
@@ -77,6 +78,7 @@ extern void _PyMem_ArenaFree(void *, void *, size_t);
         PYMEM_ALLOC, \
         PYOBJ_ALLOC, \
     }
+# define _pymem_is_debug_enabled_INIT 0
 #endif
 
 #define _pymem_allocators_debug_INIT \
diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h
index d324a94..5f47d60 100644
--- a/Include/internal/pycore_runtime_init.h
+++ b/Include/internal/pycore_runtime_init.h
@@ -86,6 +86,7 @@ extern PyTypeObject _PyExc_MemoryError;
             .standard = _pymem_allocators_standard_INIT(runtime), \
             .debug = _pymem_allocators_debug_INIT, \
             .obj_arena = _pymem_allocators_obj_arena_INIT, \
+            .is_debug_enabled = _pymem_is_debug_enabled_INIT, \
         }, \
         .obmalloc = _obmalloc_global_state_INIT, \
         .pyhash_state = pyhash_state_INIT, \
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 88ad305..16d5bcb 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -439,12 +439,14 @@ set_up_allocators_unlocked(PyMemAllocatorName allocator)
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_RAW, pydebug, NULL);
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_MEM, pydebug, NULL);
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_OBJ, pydebug, NULL);
+        _PyRuntime.allocators.is_debug_enabled = pydebug;
         break;
 
     case PYMEM_ALLOCATOR_DEBUG:
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_RAW, 1, NULL);
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_MEM, 1, NULL);
         (void)set_default_allocator_unlocked(PYMEM_DOMAIN_OBJ, 1, NULL);
+        _PyRuntime.allocators.is_debug_enabled = 1;
         break;
 
 #ifdef WITH_PYMALLOC
@@ -458,7 +460,9 @@ set_up_allocators_unlocked(PyMemAllocatorName allocator)
         set_allocator_unlocked(PYMEM_DOMAIN_MEM, &pymalloc);
         set_allocator_unlocked(PYMEM_DOMAIN_OBJ, &pymalloc);
 
-        if (allocator == PYMEM_ALLOCATOR_PYMALLOC_DEBUG) {
+        int is_debug = (allocator == PYMEM_ALLOCATOR_PYMALLOC_DEBUG);
+        _PyRuntime.allocators.is_debug_enabled = is_debug;
+        if (is_debug) {
             set_up_debug_hooks_unlocked();
         }
         break;
@@ -477,7 +481,9 @@ set_up_allocators_unlocked(PyMemAllocatorName allocator)
         PyMemAllocatorEx objmalloc = MIMALLOC_OBJALLOC;
         set_allocator_unlocked(PYMEM_DOMAIN_OBJ, &objmalloc);
 
-        if (allocator == PYMEM_ALLOCATOR_MIMALLOC_DEBUG) {
+        int is_debug = (allocator == PYMEM_ALLOCATOR_MIMALLOC_DEBUG);
+        _PyRuntime.allocators.is_debug_enabled = is_debug;
+        if (is_debug) {
             set_up_debug_hooks_unlocked();
         }
 
@@ -493,7 +499,9 @@ set_up_allocators_unlocked(PyMemAllocatorName allocator)
         set_allocator_unlocked(PYMEM_DOMAIN_MEM, &malloc_alloc);
         set_allocator_unlocked(PYMEM_DOMAIN_OBJ, &malloc_alloc);
 
-        if (allocator == PYMEM_ALLOCATOR_MALLOC_DEBUG) {
+        int is_debug = (allocator == PYMEM_ALLOCATOR_MALLOC_DEBUG);
+        _PyRuntime.allocators.is_debug_enabled = is_debug;
+        if (is_debug) {
             set_up_debug_hooks_unlocked();
         }
         break;
@@ -604,13 +612,13 @@ _PyMem_GetCurrentAllocatorName(void)
 }
 
 
-#ifdef WITH_PYMALLOC
-static int
+int
 _PyMem_DebugEnabled(void)
 {
-    return (_PyObject.malloc == _PyMem_DebugMalloc);
+    return _PyRuntime.allocators.is_debug_enabled;
 }
 
+#ifdef WITH_PYMALLOC
 static int
 _PyMem_PymallocEnabled(void)
 {
@@ -695,6 +703,7 @@ set_up_debug_hooks_unlocked(void)
     set_up_debug_hooks_domain_unlocked(PYMEM_DOMAIN_RAW);
     set_up_debug_hooks_domain_unlocked(PYMEM_DOMAIN_MEM);
     set_up_debug_hooks_domain_unlocked(PYMEM_DOMAIN_OBJ);
+    _PyRuntime.allocators.is_debug_enabled = 1;
 }
 
 void