From 4f78f7238179068530012aa51079e3c91f2a3ceb Mon Sep 17 00:00:00 2001 From: Victor Stinner Date: Tue, 30 Nov 2021 11:28:43 +0100 Subject: [PATCH] bpo-45476: Add _Py_RVALUE() macro Add a new _Py_RVALUE() macro to prevent using an expression as an l-value. Replace a "(void)" cast with the _Py_RVALUE() macro in the following macros: * PyCell_SET() * PyList_SET_ITEM() * PyTuple_SET_ITEM() * _PyGCHead_SET_FINALIZED() * _PyGCHead_SET_NEXT() * asdl_seq_SET() * asdl_seq_SET_UNTYPED() Add also parentheses around macro arguments in PyCell_SET() and PyTuple_SET_ITEM(). --- Include/cpython/cellobject.h | 2 +- Include/cpython/listobject.h | 2 +- Include/cpython/tupleobject.h | 2 +- Include/internal/pycore_asdl.h | 4 ++-- Include/internal/pycore_gc.h | 4 ++-- Include/pymacro.h | 4 ++++ 6 files changed, 11 insertions(+), 7 deletions(-) diff --git a/Include/cpython/cellobject.h b/Include/cpython/cellobject.h index 8dc7b8f4cf6f88..e07f9d1de79423 100644 --- a/Include/cpython/cellobject.h +++ b/Include/cpython/cellobject.h @@ -22,7 +22,7 @@ PyAPI_FUNC(PyObject *) PyCell_Get(PyObject *); PyAPI_FUNC(int) PyCell_Set(PyObject *, PyObject *); #define PyCell_GET(op) (((PyCellObject *)(op))->ob_ref) -#define PyCell_SET(op, v) ((void)(((PyCellObject *)(op))->ob_ref = v)) +#define PyCell_SET(op, v) _Py_RVALUE(((PyCellObject *)(op))->ob_ref = (v)) #ifdef __cplusplus } diff --git a/Include/cpython/listobject.h b/Include/cpython/listobject.h index e3239152c497c2..51687d866ce971 100644 --- a/Include/cpython/listobject.h +++ b/Include/cpython/listobject.h @@ -30,5 +30,5 @@ PyAPI_FUNC(void) _PyList_DebugMallocStats(FILE *out); #define _PyList_CAST(op) (assert(PyList_Check(op)), (PyListObject *)(op)) #define PyList_GET_ITEM(op, i) (_PyList_CAST(op)->ob_item[i]) -#define PyList_SET_ITEM(op, i, v) ((void)(_PyList_CAST(op)->ob_item[i] = (v))) +#define PyList_SET_ITEM(op, i, v) _Py_RVALUE(_PyList_CAST(op)->ob_item[i] = (v)) #define PyList_GET_SIZE(op) Py_SIZE(_PyList_CAST(op)) diff --git a/Include/cpython/tupleobject.h b/Include/cpython/tupleobject.h index 7cada8848c49fc..fc37c4e6de1cab 100644 --- a/Include/cpython/tupleobject.h +++ b/Include/cpython/tupleobject.h @@ -23,6 +23,6 @@ PyAPI_FUNC(void) _PyTuple_MaybeUntrack(PyObject *); #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i]) /* Macro, *only* to be used to fill in brand new tuples */ -#define PyTuple_SET_ITEM(op, i, v) ((void)(_PyTuple_CAST(op)->ob_item[i] = v)) +#define PyTuple_SET_ITEM(op, i, v) _Py_RVALUE(_PyTuple_CAST(op)->ob_item[i] = (v)) PyAPI_FUNC(void) _PyTuple_DebugMallocStats(FILE *out); diff --git a/Include/internal/pycore_asdl.h b/Include/internal/pycore_asdl.h index 2929e030872d94..d00a7f04e6d002 100644 --- a/Include/internal/pycore_asdl.h +++ b/Include/internal/pycore_asdl.h @@ -91,7 +91,7 @@ asdl_ ## NAME ## _seq *_Py_asdl_ ## NAME ## _seq_new(Py_ssize_t size, PyArena *a (S)->typed_elements[_asdl_i] = (V); \ } while (0) #else -# define asdl_seq_SET(S, I, V) ((void)((S)->typed_elements[I] = (V))) +# define asdl_seq_SET(S, I, V) _Py_RVALUE((S)->typed_elements[I] = (V)) #endif #ifdef Py_DEBUG @@ -103,7 +103,7 @@ asdl_ ## NAME ## _seq *_Py_asdl_ ## NAME ## _seq_new(Py_ssize_t size, PyArena *a (S)->elements[_asdl_i] = (V); \ } while (0) #else -# define asdl_seq_SET_UNTYPED(S, I, V) ((void)((S)->elements[I] = (V))) +# define asdl_seq_SET_UNTYPED(S, I, V) _Py_RVALUE((S)->elements[I] = (V)) #endif #ifdef __cplusplus diff --git a/Include/internal/pycore_gc.h b/Include/internal/pycore_gc.h index 129d53921dc49b..a23dca805491d0 100644 --- a/Include/internal/pycore_gc.h +++ b/Include/internal/pycore_gc.h @@ -43,7 +43,7 @@ typedef struct { // Lowest bit of _gc_next is used for flags only in GC. // But it is always 0 for normal code. #define _PyGCHead_NEXT(g) ((PyGC_Head*)(g)->_gc_next) -#define _PyGCHead_SET_NEXT(g, p) ((void)((g)->_gc_next = (uintptr_t)(p))) +#define _PyGCHead_SET_NEXT(g, p) _Py_RVALUE((g)->_gc_next = (uintptr_t)(p)) // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags. #define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK)) @@ -56,7 +56,7 @@ typedef struct { #define _PyGCHead_FINALIZED(g) \ (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0) #define _PyGCHead_SET_FINALIZED(g) \ - ((void)((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED)) + _Py_RVALUE((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED) #define _PyGC_FINALIZED(o) \ _PyGCHead_FINALIZED(_Py_AS_GC(o)) diff --git a/Include/pymacro.h b/Include/pymacro.h index 202b936d964f00..2728496976de7e 100644 --- a/Include/pymacro.h +++ b/Include/pymacro.h @@ -129,4 +129,8 @@ Py_FatalError("Unreachable C code path reached") #endif +// Prevent using an expression as a l-value. +// For example, "int x; _Py_RVALUE(x) = 1;" fails with a compiler error. +#define _Py_RVALUE(EXPR) ((void)0, (EXPR)) + #endif /* Py_PYMACRO_H */