Include/pymacro.h - main - githubmirror/cpython

Include/pymacro.h
294 строки12 KB
Serhiy Storchaka
gh-141370: Fix undefined behavior when using Py_ABS() (GH-141548)
05 дек 2025, 17:24
05 дек 2025, 17:24706fdda
#ifndef Py_PYMACRO_H
#define Py_PYMACRO_H

// gh-91782: On FreeBSD 12, if the _POSIX_C_SOURCE and _XOPEN_SOURCE macros are
// defined, <sys/cdefs.h> disables C11 support and <assert.h> does not define
// the static_assert() macro.
// https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255290
//
// macOS <= 10.10 doesn't define static_assert in assert.h at all despite
// having C11 compiler support.
//
// static_assert is defined in glibc from version 2.16. Compiler support for
// the C11 _Static_assert keyword is in gcc >= 4.6.
//
// MSVC makes static_assert a keyword in C11-17, contrary to the standards.
//
// In C++11 and C2x, static_assert is a keyword, redefining is undefined
// behaviour. So only define if building as C, not C++ (if __cplusplus is
// not defined), and only for C11-17.
#if !defined(static_assert) && (defined(__GNUC__) || defined(__clang__)) \
     && !defined(__cplusplus) && defined(__STDC_VERSION__) \
     && __STDC_VERSION__ >= 201112L && __STDC_VERSION__ <= 201710L
#  define static_assert _Static_assert
#endif


// _Py_ALIGNED_DEF(N, T): Define a variable/member with increased alignment
//
// `N`: the desired minimum alignment, an integer literal, number of bytes
// `T`: the type of the defined variable
//      (or a type with at least the defined variable's alignment)
//
// May not be used on a struct definition.
//
// Standards/compiler support for `alignas` alternatives:
// - `alignas` is a keyword in C23 and C++11.
// - `_Alignas` is a keyword in C11
// - GCC & clang has __attribute__((aligned))
//   (use that for older standards in pedantic mode)
// - MSVC has __declspec(align)
// - `_Alignas` is common C compiler extension
// Older compilers may name `alignas` differently; to allow compilation on such
// unsupported platforms, we don't redefine _Py_ALIGNED_DEF if it's already
// defined. Note that defining it wrong (including defining it to nothing) will
// cause ABI incompatibilities.
//
// Behavior of `alignas` alternatives:
// - `alignas` & `_Alignas`:
//   - Can be used multiple times; the greatest alignment applies.
//   - It is an *error* if the combined effect of all `alignas` modifiers would
//     decrease the alignment.
//   - Takes types or numbers.
//   - May not be used on a struct definition, unless also defining a variable.
// - `__declspec(align)`:
//   - Has no effect if it would decrease alignment.
//   - Only takes an integer literal.
//   - May be used on struct or variable definitions.
//     However, when defining both the struct and the variable at once,
//     `declspec(aligned)` causes compiler warning 5274 and possible ABI
//     incompatibility.
// - ` __attribute__((aligned))`:
//   - Has no effect if it would decrease alignment.
//   - Takes types or numbers
//   - May be used on struct or variable definitions.
#ifndef _Py_ALIGNED_DEF
#    ifdef __cplusplus
#        if __cplusplus >= 201103L
#            define _Py_ALIGNED_DEF(N, T) alignas(N) alignas(T) T
#        elif defined(__GNUC__) || defined(__clang__)
#            define _Py_ALIGNED_DEF(N, T) __attribute__((aligned(N))) T
#        elif defined(_MSC_VER)
#            define _Py_ALIGNED_DEF(N, T) __declspec(align(N)) T
#        else
#            define _Py_ALIGNED_DEF(N, T) alignas(N) alignas(T) T
#        endif
#    elif defined(_MSC_VER)
#        define _Py_ALIGNED_DEF(N, T) __declspec(align(N)) T
#    elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
#        define _Py_ALIGNED_DEF(N, T) alignas(N) alignas(T) T
#    elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
#        define _Py_ALIGNED_DEF(N, T)  _Alignas(N) _Alignas(T) T
#    elif (defined(__GNUC__) || defined(__clang__))
#        define _Py_ALIGNED_DEF(N, T) __attribute__((aligned(N))) T
#    else
#        define _Py_ALIGNED_DEF(N, T) _Alignas(N) _Alignas(T) T
#    endif
#endif


// _Py_ANONYMOUS: modifier for declaring an anonymous union.
// Usage: _Py_ANONYMOUS union { ... };
// Standards/compiler support:
// - C++ allows anonymous unions, but not structs
// - C11 and above allows anonymous unions and structs
// - MSVC has warning(disable: 4201) "nonstandard extension used : nameless
//   struct/union". This is specific enough that we disable it for all of
//   Python.h.
// - GCC & clang needs __extension__ before C11
// To allow unsupported platforms which need other spellings, we use a
// predefined value of _Py_ANONYMOUS if it exists.
#ifndef _Py_ANONYMOUS
#   if (defined(__GNUC__) || defined(__clang__)) \
          && !(defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)
#       define _Py_ANONYMOUS __extension__
#   else
#       define _Py_ANONYMOUS
#   endif
#endif


/* Minimum value between x and y */
#define Py_MIN(x, y) (((x) > (y)) ? (y) : (x))

/* Maximum value between x and y */
#define Py_MAX(x, y) (((x) > (y)) ? (x) : (y))

/* Absolute value of the number x */
#define Py_ABS(x) ((x) < 0 ? -(x) : (x))
/* Safer implementation that avoids an undefined behavior for the minimal
   value of the signed integer type if its absolute value is larger than
   the maximal value of the signed integer type (in the two's complement
   representations, which is common).
 */
#define _Py_ABS_CAST(T, x) ((x) >= 0 ? ((T) (x)) : ((T) (((T) -((x) + 1)) + 1u)))

#define _Py_XSTRINGIFY(x) #x

/* Convert the argument to a string. For example, Py_STRINGIFY(123) is replaced
   with "123" by the preprocessor. Defines are also replaced by their value.
   For example Py_STRINGIFY(__LINE__) is replaced by the line number, not
   by "__LINE__". */
#define Py_STRINGIFY(x) _Py_XSTRINGIFY(x)

/* Get the size of a structure member in bytes */
#define Py_MEMBER_SIZE(type, member) sizeof(((type *)0)->member)

/* Argument must be a char or an int in [-128, 127] or [0, 255]. */
#define Py_CHARMASK(c) ((unsigned char)((c) & 0xff))

#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L \
     && !defined(__cplusplus) && !defined(_MSC_VER))
#  define Py_BUILD_ASSERT_EXPR(cond) \
    ((void)sizeof(struct { int dummy; _Static_assert(cond, #cond); }), \
     0)
#else
   /* Assert a build-time dependency, as an expression.
    *
    * Your compile will fail if the condition isn't true, or can't be evaluated
    * by the compiler. This can be used in an expression: its value is 0.
    *
    * Example:
    *
    * #define foo_to_char(foo)  \
    *     ((char *)(foo)        \
    *      + Py_BUILD_ASSERT_EXPR(offsetof(struct foo, string) == 0))
    *
    * Written by Rusty Russell, public domain, http://ccodearchive.net/
    */
#  define Py_BUILD_ASSERT_EXPR(cond) \
    (sizeof(char [1 - 2*!(cond)]) - 1)
#endif

#if ((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) \
     || (defined(__cplusplus) && __cplusplus >= 201103L))
   // Use static_assert() on C11 and newer
#  define Py_BUILD_ASSERT(cond) \
        do { \
            static_assert((cond), #cond); \
        } while (0)
#else
#  define Py_BUILD_ASSERT(cond)  \
        do { \
            (void)Py_BUILD_ASSERT_EXPR(cond); \
        } while(0)
#endif

/* Get the number of elements in a visible array

   This does not work on pointers, or arrays declared as [], or function
   parameters. With correct compiler support, such usage will cause a build
   error (see Py_BUILD_ASSERT_EXPR).

   Written by Rusty Russell, public domain, http://ccodearchive.net/

   Requires at GCC 3.1+ */
#if (defined(__GNUC__) && !defined(__STRICT_ANSI__) && \
    (((__GNUC__ == 3) && (__GNUC_MINOR__ >= 1)) || (__GNUC__ >= 4)))
/* Two gcc extensions.
   &a[0] degrades to a pointer: a different type from an array */
#define Py_ARRAY_LENGTH(array) \
    (sizeof(array) / sizeof((array)[0]) \
     + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
                                                          typeof(&(array)[0]))))
#else
#define Py_ARRAY_LENGTH(array) \
    (sizeof(array) / sizeof((array)[0]))
#endif


/* Define macros for inline documentation. */
#define PyDoc_VAR(name) static const char name[]
#define PyDoc_STRVAR(name,str) PyDoc_VAR(name) = PyDoc_STR(str)
#ifdef WITH_DOC_STRINGS
#define PyDoc_STR(str) str
#else
#define PyDoc_STR(str) ""
#endif

/* Below "a" is a power of 2. */
/* Round down size "n" to be a multiple of "a". */
#define _Py_SIZE_ROUND_DOWN(n, a) ((size_t)(n) & ~(size_t)((a) - 1))
/* Round up size "n" to be a multiple of "a". */
#define _Py_SIZE_ROUND_UP(n, a) (((size_t)(n) + \
        (size_t)((a) - 1)) & ~(size_t)((a) - 1))
/* Round pointer "p" down to the closest "a"-aligned address <= "p". */
#define _Py_ALIGN_DOWN(p, a) ((void *)((uintptr_t)(p) & ~(uintptr_t)((a) - 1)))
/* Round pointer "p" up to the closest "a"-aligned address >= "p". */
#define _Py_ALIGN_UP(p, a) ((void *)(((uintptr_t)(p) + \
        (uintptr_t)((a) - 1)) & ~(uintptr_t)((a) - 1)))
/* Check if pointer "p" is aligned to "a"-bytes boundary. */
#define _Py_IS_ALIGNED(p, a) (!((uintptr_t)(p) & (uintptr_t)((a) - 1)))

/* Use this for unused arguments in a function definition to silence compiler
 * warnings. Example:
 *
 * int func(int a, int Py_UNUSED(b)) { return a; }
 */
#if defined(__GNUC__) || defined(__clang__)
#  define Py_UNUSED(name) _unused_ ## name __attribute__((unused))
#elif defined(_MSC_VER)
   // Disable warning C4100: unreferenced formal parameter,
   // declare the parameter,
   // restore old compiler warnings.
#  define Py_UNUSED(name) \
        __pragma(warning(push)) \
        __pragma(warning(suppress: 4100)) \
        _unused_ ## name \
        __pragma(warning(pop))
#else
#  define Py_UNUSED(name) _unused_ ## name
#endif

#if defined(RANDALL_WAS_HERE)
#  define Py_UNREACHABLE() \
    Py_FatalError( \
        "If you're seeing this, the code is in what I thought was\n" \
        "an unreachable state.\n\n" \
        "I could give you advice for what to do, but honestly, why\n" \
        "should you trust me?  I clearly screwed this up.  I'm writing\n" \
        "a message that should never appear, yet I know it will\n" \
        "probably appear someday.\n\n" \
        "On a deep level, I know I'm not up to this task.\n" \
        "I'm so sorry.\n" \
        "https://xkcd.com/2200")
#elif defined(Py_DEBUG)
#  define Py_UNREACHABLE() \
    Py_FatalError( \
        "We've reached an unreachable state. Anything is possible.\n" \
        "The limits were in our heads all along. Follow your dreams.\n" \
        "https://xkcd.com/2200")
#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5))
#  define Py_UNREACHABLE() __builtin_unreachable()
#elif defined(__clang__) || defined(__INTEL_COMPILER)
#  define Py_UNREACHABLE() __builtin_unreachable()
#elif defined(_MSC_VER)
#  define Py_UNREACHABLE() __assume(0)
#else
#  define Py_UNREACHABLE() \
    Py_FatalError("Unreachable C code path reached")
#endif

#define _Py_CONTAINER_OF(ptr, type, member) \
    (type*)((char*)ptr - offsetof(type, member))

// 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))

// Return non-zero if the type is signed, return zero if it's unsigned.
// Use "<= 0" rather than "< 0" to prevent the compiler warning:
// "comparison of unsigned expression in '< 0' is always false".
#define _Py_IS_TYPE_SIGNED(type) ((type)(-1) <= 0)

// Version helpers. These are primarily macros, but have exported equivalents.
#define _Py_PACK_VERSION(X, Y) _Py_PACK_FULL_VERSION(X, Y, 0, 0, 0)
#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= _Py_PACK_VERSION(3, 14)
PyAPI_FUNC(uint32_t) Py_PACK_FULL_VERSION(int x, int y, int z, int level, int serial);
PyAPI_FUNC(uint32_t) Py_PACK_VERSION(int x, int y);
#define Py_PACK_FULL_VERSION _Py_PACK_FULL_VERSION
#define Py_PACK_VERSION _Py_PACK_VERSION
#endif // Py_LIMITED_API < 3.14


#endif /* Py_PYMACRO_H */