unsigned char race

python · colesbury · Dec 3, 2024 · Aug 21, 2024 · Aug 21, 2024 · Aug 22, 2024
commit d9614b743743c1ebbd34f9b145dbdfb40b64d2c3
diff --git a/Include/cpython/pyatomic.h b/Include/cpython/pyatomic.h
@@ -324,6 +324,9 @@ _Py_atomic_load_int_relaxed(const int *obj);
 static inline char
 _Py_atomic_load_char_relaxed(const char *obj);
 
+static inline unsigned char
+_Py_atomic_load_uchar_relaxed(const unsigned char *obj);
+
 static inline int8_t
 _Py_atomic_load_int8_relaxed(const int8_t *obj);
 
@@ -487,6 +490,9 @@ _Py_atomic_store_int_release(int *obj, int value);
 static inline void
 _Py_atomic_store_char_release(char *obj, char value);
 
+static inline void
+_Py_atomic_store_uchar_release(unsigned char *obj, unsigned char value);
+
 static inline int
 _Py_atomic_load_int_acquire(const int *obj);
 

diff --git a/Include/cpython/pyatomic_gcc.h b/Include/cpython/pyatomic_gcc.h
@@ -310,6 +310,10 @@ static inline char
 _Py_atomic_load_char_relaxed(const char *obj)
 { return __atomic_load_n(obj, __ATOMIC_RELAXED); }
 
+static inline unsigned char
+_Py_atomic_load_uchar_relaxed(const unsigned char *obj)
+{ return __atomic_load_n(obj, __ATOMIC_RELAXED); }
+
 static inline int8_t
 _Py_atomic_load_int8_relaxed(const int8_t *obj)
 { return __atomic_load_n(obj, __ATOMIC_RELAXED); }
@@ -516,6 +520,10 @@ static inline void
 _Py_atomic_store_char_release(char *obj, char value)
 { __atomic_store_n(obj, value, __ATOMIC_RELEASE); }
 
+static inline void
+_Py_atomic_store_uchar_release(unsigned char *obj, unsigned char value)
+{ __atomic_store_n(obj, value, __ATOMIC_RELEASE); }
+
 static inline void
 _Py_atomic_store_ssize_release(Py_ssize_t *obj, Py_ssize_t value)
 { __atomic_store_n(obj, value, __ATOMIC_RELEASE); }

diff --git a/Include/cpython/pyatomic_msc.h b/Include/cpython/pyatomic_msc.h
@@ -983,6 +983,19 @@ _Py_atomic_store_char_release(char *obj, char value)
 #endif
 }
 
+static inline void
+_Py_atomic_store_uchar_release(unsigned char *obj, unsigned char value)
+{
+#if defined(_M_X64) || defined(_M_IX86)
+    *(unsigned char volatile *)obj = value;
+#elif defined(_M_ARM64)
+    _Py_atomic_ASSERT_ARG_TYPE(unsigned __int8);
+    __stlr8((unsigned __int8 volatile *)obj, (unsigned __int8)value);
+#else
+#  error "no implementation of _Py_atomic_store_uchar_release"
+#endif
+}
+
 static inline void
 _Py_atomic_store_ssize_release(Py_ssize_t *obj, Py_ssize_t value)
 {

diff --git a/Include/cpython/pyatomic_std.h b/Include/cpython/pyatomic_std.h
@@ -523,6 +523,14 @@ _Py_atomic_load_char_relaxed(const char *obj)
                                 memory_order_relaxed);
 }
 
+static inline unsigned char
+_Py_atomic_load_uchar_relaxed(const unsigned char *obj)
+{
+    _Py_USING_STD;
+    return atomic_load_explicit((const _Atomic(unsigned char)*)obj,
+                                memory_order_relaxed);
+}
+
 static inline int8_t
 _Py_atomic_load_int8_relaxed(const int8_t *obj)
 {
@@ -911,6 +919,14 @@ _Py_atomic_store_char_release(char *obj, char value)
                           memory_order_release);
 }
 
+static inline void
+_Py_atomic_store_uchar_release(unsigned char *obj, unsigned char value)
+{
+    _Py_USING_STD;
+    atomic_store_explicit((_Atomic(unsigned char)*)obj, value,
+                          memory_order_release);
+}
+
 static inline void
 _Py_atomic_store_ssize_release(Py_ssize_t *obj, Py_ssize_t value)
 {

diff --git a/Include/internal/pycore_pyatomic_ft_wrappers.h b/Include/internal/pycore_pyatomic_ft_wrappers.h
@@ -65,6 +65,10 @@ extern "C" {
     _Py_atomic_store_char_release(&value, new_value)
 #define FT_ATOMIC_LOAD_CHAR_RELAXED(value) \
     _Py_atomic_load_char_relaxed(&value)
+#define FT_ATOMIC_STORE_UCHAR_RELEASE(value, new_value) \
+    _Py_atomic_store_uchar_release(&value, new_value)
+#define FT_ATOMIC_LOAD_UCHAR_RELAXED(value) \
+    _Py_atomic_load_uchar_relaxed(&value)
 
 #else
 #define FT_ATOMIC_LOAD_PTR(value) value
@@ -90,6 +94,8 @@ extern "C" {
 #define FT_ATOMIC_STORE_UINT32_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_LOAD_CHAR_RELAXED(value) value
 #define FT_ATOMIC_STORE_CHAR_RELEASE(value, new_value) value = new_value
+#define FT_ATOMIC_LOAD_UCHAR_RELAXED(value) value
+#define FT_ATOMIC_STORE_UCHAR_RELEASE(value, new_value) value = new_value
 
 #endif
 

diff --git a/Python/structmember.c b/Python/structmember.c
@@ -40,7 +40,7 @@ PyMember_GetOne(const char *obj_addr, PyMemberDef *l)
         v = PyLong_FromLong(FT_ATOMIC_LOAD_CHAR_RELAXED(*(char*)addr));
        break;
     case Py_T_UBYTE:
-        v = PyLong_FromUnsignedLong(*(unsigned char*)addr);
+        v = PyLong_FromUnsignedLong(FT_ATOMIC_LOAD_UCHAR_RELAXED(*(unsigned char*)addr));
         break;
     case Py_T_SHORT:
         v = PyLong_FromLong(*(short*)addr);
@@ -189,7 +189,7 @@ PyMember_SetOne(char *addr, PyMemberDef *l, PyObject *v)
         long long_val = PyLong_AsLong(v);
         if ((long_val == -1) && PyErr_Occurred())
             return -1;
-        *(unsigned char*)addr = (unsigned char)long_val;
+        FT_ATOMIC_STORE_UCHAR_RELEASE(*(unsigned char*)addr, (unsigned char)long_val);
         if ((long_val > UCHAR_MAX) || (long_val < 0))
             WARN("Truncation of value to unsigned char");
         break;