/* Frame object implementation */

#include "Python.h"
#include "pycore_ceval.h"         // _PyEval_BuiltinsFromGlobals()
#include "pycore_moduleobject.h"  // _PyModule_GetDict()
#include "pycore_object.h"        // _PyObject_GC_UNTRACK()

#include "frameobject.h"          // PyFrameObject
#include "pycore_frame.h"
#include "opcode.h"               // EXTENDED_ARG
#include "structmember.h"         // PyMemberDef

#define OFF(x) offsetof(PyFrameObject, x)

static PyMemberDef frame_memberlist[] = {
    {"f_back",          T_OBJECT,       OFF(f_back),      READONLY},
    {"f_trace_lines",   T_BOOL,         OFF(f_trace_lines), 0},
    {"f_trace_opcodes", T_BOOL,         OFF(f_trace_opcodes), 0},
    {NULL}      /* Sentinel */
};

static struct _Py_frame_state *
get_frame_state(void)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    return &interp->frame;
}


static PyObject *
frame_getlocals(PyFrameObject *f, void *closure)
{
    if (PyFrame_FastToLocalsWithError(f) < 0)
        return NULL;
    PyObject *locals = _PyFrame_Specials(f)[FRAME_SPECIALS_LOCALS_OFFSET];
    Py_INCREF(locals);
    return locals;
}

int
PyFrame_GetLineNumber(PyFrameObject *f)
{
    assert(f != NULL);
    if (f->f_lineno != 0) {
        return f->f_lineno;
    }
    else {
        return PyCode_Addr2Line(f->f_code, f->f_lasti*2);
    }
}

static PyObject *
frame_getlineno(PyFrameObject *f, void *closure)
{
    int lineno = PyFrame_GetLineNumber(f);
    if (lineno < 0) {
        Py_RETURN_NONE;
    }
    else {
        return PyLong_FromLong(lineno);
    }
}

static PyObject *
frame_getlasti(PyFrameObject *f, void *closure)
{
    if (f->f_lasti < 0) {
        return PyLong_FromLong(-1);
    }
    return PyLong_FromLong(f->f_lasti*2);
}

static PyObject *
frame_getglobals(PyFrameObject *f, void *closure)
{
    PyObject *globals = _PyFrame_GetGlobals(f);
    if (globals == NULL) {
        globals = Py_None;
    }
    Py_INCREF(globals);
    return globals;
}

static PyObject *
frame_getbuiltins(PyFrameObject *f, void *closure)
{
    PyObject *builtins = _PyFrame_GetBuiltins(f);
    if (builtins == NULL) {
        builtins = Py_None;
    }
    Py_INCREF(builtins);
    return builtins;
}

static PyObject *
frame_getcode(PyFrameObject *f, void *closure)
{
    if (PySys_Audit("object.__getattr__", "Os", f, "f_code") < 0) {
        return NULL;
    }
    return (PyObject *)PyFrame_GetCode(f);
}

/* Given the index of the effective opcode,
   scan back to construct the oparg with EXTENDED_ARG */
static unsigned int
get_arg(const _Py_CODEUNIT *codestr, Py_ssize_t i)
{
    _Py_CODEUNIT word;
    unsigned int oparg = _Py_OPARG(codestr[i]);
    if (i >= 1 && _Py_OPCODE(word = codestr[i-1]) == EXTENDED_ARG) {
        oparg |= _Py_OPARG(word) << 8;
        if (i >= 2 && _Py_OPCODE(word = codestr[i-2]) == EXTENDED_ARG) {
            oparg |= _Py_OPARG(word) << 16;
            if (i >= 3 && _Py_OPCODE(word = codestr[i-3]) == EXTENDED_ARG) {
                oparg |= _Py_OPARG(word) << 24;
            }
        }
    }
    return oparg;
}

/* Model the evaluation stack, to determine which jumps
 * are safe and how many values needs to be popped.
 * The stack is modelled by a 64 integer, treating any
 * stack that can't fit into 64 bits as "overflowed".
 */

typedef enum kind {
    Iterator = 1,
    Except = 2,
    Object = 3,
} Kind;

#define BITS_PER_BLOCK 2

#define UNINITIALIZED -2
#define OVERFLOWED -1

#define MAX_STACK_ENTRIES (63/BITS_PER_BLOCK)
#define WILL_OVERFLOW (1ULL<<((MAX_STACK_ENTRIES-1)*BITS_PER_BLOCK))

static inline int64_t
push_value(int64_t stack, Kind kind)
{
    if (((uint64_t)stack) >= WILL_OVERFLOW) {
        return OVERFLOWED;
    }
    else {
        return (stack << BITS_PER_BLOCK) | kind;
    }
}

static inline int64_t
pop_value(int64_t stack)
{
    return Py_ARITHMETIC_RIGHT_SHIFT(int64_t, stack, BITS_PER_BLOCK);
}

static inline Kind
top_of_stack(int64_t stack)
{
    return stack & ((1<<BITS_PER_BLOCK)-1);
}

static int64_t *
mark_stacks(PyCodeObject *code_obj, int len)
{
    const _Py_CODEUNIT *code =
        (const _Py_CODEUNIT *)PyBytes_AS_STRING(code_obj->co_code);
    int64_t *stacks = PyMem_New(int64_t, len+1);
    int i, j, opcode;

    if (stacks == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    for (int i = 1; i <= len; i++) {
        stacks[i] = UNINITIALIZED;
    }
    stacks[0] = 0;
    int todo = 1;
    while (todo) {
        todo = 0;
        for (i = 0; i < len; i++) {
            int64_t next_stack = stacks[i];
            if (next_stack == UNINITIALIZED) {
                continue;
            }
            opcode = _Py_OPCODE(code[i]);
            switch (opcode) {
                case JUMP_IF_FALSE_OR_POP:
                case JUMP_IF_TRUE_OR_POP:
                case POP_JUMP_IF_FALSE:
                case POP_JUMP_IF_TRUE:
                case JUMP_IF_NOT_EXC_MATCH:
                {
                    int64_t target_stack;
                    int j = get_arg(code, i);
                    assert(j < len);
                    if (stacks[j] == UNINITIALIZED && j < i) {
                        todo = 1;
                    }
                    if (opcode == JUMP_IF_NOT_EXC_MATCH) {
                        next_stack = pop_value(pop_value(next_stack));
                        target_stack = next_stack;
                    }
                    else if (opcode == JUMP_IF_FALSE_OR_POP ||
                             opcode == JUMP_IF_TRUE_OR_POP)
                    {
                        target_stack = next_stack;
                        next_stack = pop_value(next_stack);
                    }
                    else {
                        next_stack = pop_value(next_stack);
                        target_stack = next_stack;
                    }
                    assert(stacks[j] == UNINITIALIZED || stacks[j] == target_stack);
                    stacks[j] = target_stack;
                    stacks[i+1] = next_stack;
                    break;
                }
                case JUMP_ABSOLUTE:
                    j = get_arg(code, i);
                    assert(j < len);
                    if (stacks[j] == UNINITIALIZED && j < i) {
                        todo = 1;
                    }
                    assert(stacks[j] == UNINITIALIZED || stacks[j] == next_stack);
                    stacks[j] = next_stack;
                    break;
                case POP_EXCEPT:
                    next_stack = pop_value(pop_value(pop_value(next_stack)));
                    stacks[i+1] = next_stack;
                    break;

                case JUMP_FORWARD:
                    j = get_arg(code, i) + i + 1;
                    assert(j < len);
                    assert(stacks[j] == UNINITIALIZED || stacks[j] == next_stack);
                    stacks[j] = next_stack;
                    break;
                case GET_ITER:
                case GET_AITER:
                    next_stack = push_value(pop_value(next_stack), Iterator);
                    stacks[i+1] = next_stack;
                    break;
                case FOR_ITER:
                {
                    int64_t target_stack = pop_value(next_stack);
                    stacks[i+1] = push_value(next_stack, Object);
                    j = get_arg(code, i) + i + 1;
                    assert(j < len);
                    assert(stacks[j] == UNINITIALIZED || stacks[j] == target_stack);
                    stacks[j] = target_stack;
                    break;
                }
                case END_ASYNC_FOR:
                    next_stack = pop_value(pop_value(pop_value(next_stack)));
                    stacks[i+1] = next_stack;
                    break;
                case PUSH_EXC_INFO:
                    next_stack = push_value(next_stack, Except);
                    next_stack = push_value(next_stack, Except);
                    next_stack = push_value(next_stack, Except);
                    stacks[i+1] = next_stack;
                case RETURN_VALUE:
                case RAISE_VARARGS:
                case RERAISE:
                case POP_EXCEPT_AND_RERAISE:
                    /* End of block */
                    break;
                case GEN_START:
                    stacks[i+1] = next_stack;
                    break;
                default:
                {
                    int delta = PyCompile_OpcodeStackEffect(opcode, _Py_OPARG(code[i]));
                    while (delta < 0) {
                        next_stack = pop_value(next_stack);
                        delta++;
                    }
                    while (delta > 0) {
                        next_stack = push_value(next_stack, Object);
                        delta--;
                    }
                    stacks[i+1] = next_stack;
                }
            }
        }
    }
    return stacks;
}

static int
compatible_kind(Kind from, Kind to) {
    if (to == 0) {
        return 0;
    }
    if (to == Object) {
        return 1;
    }
    return from == to;
}

static int
compatible_stack(int64_t from_stack, int64_t to_stack)
{
    if (from_stack < 0 || to_stack < 0) {
        return 0;
    }
    while(from_stack > to_stack) {
        from_stack = pop_value(from_stack);
    }
    while(from_stack) {
        Kind from_top = top_of_stack(from_stack);
        Kind to_top = top_of_stack(to_stack);
        if (!compatible_kind(from_top, to_top)) {
            return 0;
        }
        from_stack = pop_value(from_stack);
        to_stack = pop_value(to_stack);
    }
    return to_stack == 0;
}

static const char *
explain_incompatible_stack(int64_t to_stack)
{
    assert(to_stack != 0);
    if (to_stack == OVERFLOWED) {
        return "stack is too deep to analyze";
    }
    if (to_stack == UNINITIALIZED) {
        return "can't jump into an exception handler, or code may be unreachable";
    }
    Kind target_kind = top_of_stack(to_stack);
    switch(target_kind) {
        case Except:
            return "can't jump into an 'except' block as there's no exception";
        case Object:
            return "differing stack depth";
        case Iterator:
            return "can't jump into the body of a for loop";
        default:
            Py_UNREACHABLE();
    }
}

static int *
marklines(PyCodeObject *code, int len)
{
    PyCodeAddressRange bounds;
    _PyCode_InitAddressRange(code, &bounds);
    assert (bounds.ar_end == 0);

    int *linestarts = PyMem_New(int, len);
    if (linestarts == NULL) {
        return NULL;
    }
    for (int i = 0; i < len; i++) {
        linestarts[i] = -1;
    }

    while (PyLineTable_NextAddressRange(&bounds)) {
        assert(bounds.ar_start/2 < len);
        linestarts[bounds.ar_start/2] = bounds.ar_line;
    }
    return linestarts;
}

static int
first_line_not_before(int *lines, int len, int line)
{
    int result = INT_MAX;
    for (int i = 0; i < len; i++) {
        if (lines[i] < result && lines[i] >= line) {
            result = lines[i];
        }
    }
    if (result == INT_MAX) {
        return -1;
    }
    return result;
}

static void
frame_stack_pop(PyFrameObject *f)
{
    assert(f->f_stackdepth > 0);
    f->f_stackdepth--;
    PyObject *v = f->f_valuestack[f->f_stackdepth];
    Py_DECREF(v);
}

/* Setter for f_lineno - you can set f_lineno from within a trace function in
 * order to jump to a given line of code, subject to some restrictions.  Most
 * lines are OK to jump to because they don't make any assumptions about the
 * state of the stack (obvious because you could remove the line and the code
 * would still work without any stack errors), but there are some constructs
 * that limit jumping:
 *
 *  o Any excpetion handlers.
 *  o 'for' and 'async for' loops can't be jumped into because the
 *    iterator needs to be on the stack.
 *  o Jumps cannot be made from within a trace function invoked with a
 *    'return' or 'exception' event since the eval loop has been exited at
 *    that time.
 */
static int
frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno, void *Py_UNUSED(ignored))
{
    if (p_new_lineno == NULL) {
        PyErr_SetString(PyExc_AttributeError, "cannot delete attribute");
        return -1;
    }
    /* f_lineno must be an integer. */
    if (!PyLong_CheckExact(p_new_lineno)) {
        PyErr_SetString(PyExc_ValueError,
                        "lineno must be an integer");
        return -1;
    }

    /*
     * This code preserves the historical restrictions on
     * setting the line number of a frame.
     * Jumps are forbidden on a 'return' trace event (except after a yield).
     * Jumps from 'call' trace events are also forbidden.
     * In addition, jumps are forbidden when not tracing,
     * as this is a debugging feature.
     */
    switch(f->f_state) {
        case FRAME_CREATED:
            PyErr_Format(PyExc_ValueError,
                     "can't jump from the 'call' trace event of a new frame");
            return -1;
        case FRAME_RETURNED:
        case FRAME_UNWINDING:
        case FRAME_RAISED:
        case FRAME_CLEARED:
            PyErr_SetString(PyExc_ValueError,
                "can only jump from a 'line' trace event");
            return -1;
        case FRAME_EXECUTING:
        case FRAME_SUSPENDED:
            /* You can only do this from within a trace function, not via
            * _getframe or similar hackery. */
            if (!f->f_trace) {
                PyErr_Format(PyExc_ValueError,
                            "f_lineno can only be set by a trace function");
                return -1;
            }
            break;
    }

    int new_lineno;

    /* Fail if the line falls outside the code block and
        select first line with actual code. */
    int overflow;
    long l_new_lineno = PyLong_AsLongAndOverflow(p_new_lineno, &overflow);
    if (overflow
#if SIZEOF_LONG > SIZEOF_INT
        || l_new_lineno > INT_MAX
        || l_new_lineno < INT_MIN
#endif
    ) {
        PyErr_SetString(PyExc_ValueError,
                        "lineno out of range");
        return -1;
    }
    new_lineno = (int)l_new_lineno;

    if (new_lineno < f->f_code->co_firstlineno) {
        PyErr_Format(PyExc_ValueError,
                    "line %d comes before the current code block",
                    new_lineno);
        return -1;
    }

    /* PyCode_NewWithPosOnlyArgs limits co_code to be under INT_MAX so this
     * should never overflow. */
    int len = (int)(PyBytes_GET_SIZE(f->f_code->co_code) / sizeof(_Py_CODEUNIT));
    int *lines = marklines(f->f_code, len);
    if (lines == NULL) {
        return -1;
    }

    new_lineno = first_line_not_before(lines, len, new_lineno);
    if (new_lineno < 0) {
        PyErr_Format(PyExc_ValueError,
                    "line %d comes after the current code block",
                    (int)l_new_lineno);
        PyMem_Free(lines);
        return -1;
    }

    int64_t *stacks = mark_stacks(f->f_code, len);
    if (stacks == NULL) {
        PyMem_Free(lines);
        return -1;
    }

    int64_t best_stack = OVERFLOWED;
    int best_addr = -1;
    int64_t start_stack = stacks[f->f_lasti];
    int err = -1;
    const char *msg = "cannot find bytecode for specified line";
    for (int i = 0; i < len; i++) {
        if (lines[i] == new_lineno) {
            int64_t target_stack = stacks[i];
            if (compatible_stack(start_stack, target_stack)) {
                err = 0;
                if (target_stack > best_stack) {
                    best_stack = target_stack;
                    best_addr = i;
                }
            }
            else if (err < 0) {
                if (start_stack == OVERFLOWED) {
                    msg = "stack to deep to analyze";
                }
                else if (start_stack == UNINITIALIZED) {
                    msg = "can't jump from within an exception handler";
                }
                else {
                    msg = explain_incompatible_stack(target_stack);
                    err = 1;
                }
            }
        }
    }
    PyMem_Free(stacks);
    PyMem_Free(lines);
    if (err) {
        PyErr_SetString(PyExc_ValueError, msg);
        return -1;
    }
    /* Unwind block stack. */
    if (f->f_state == FRAME_SUSPENDED) {
        /* Account for value popped by yield */
        start_stack = pop_value(start_stack);
    }
    while (start_stack > best_stack) {
        frame_stack_pop(f);
        start_stack = pop_value(start_stack);
    }
    /* Finally set the new f_lasti and return OK. */
    f->f_lineno = 0;
    f->f_lasti = best_addr;
    return 0;
}

static PyObject *
frame_gettrace(PyFrameObject *f, void *closure)
{
    PyObject* trace = f->f_trace;

    if (trace == NULL)
        trace = Py_None;

    Py_INCREF(trace);

    return trace;
}

static int
frame_settrace(PyFrameObject *f, PyObject* v, void *closure)
{
    if (v == Py_None) {
        v = NULL;
    }
    Py_XINCREF(v);
    Py_XSETREF(f->f_trace, v);

    return 0;
}


static PyGetSetDef frame_getsetlist[] = {
    {"f_locals",        (getter)frame_getlocals, NULL, NULL},
    {"f_lineno",        (getter)frame_getlineno,
                    (setter)frame_setlineno, NULL},
    {"f_trace",         (getter)frame_gettrace, (setter)frame_settrace, NULL},
    {"f_lasti",         (getter)frame_getlasti, NULL, NULL},
    {"f_globals",       (getter)frame_getglobals, NULL, NULL},
    {"f_builtins",      (getter)frame_getbuiltins, NULL, NULL},
    {"f_code",          (getter)frame_getcode, NULL, NULL},
    {0}
};

/* Stack frames are allocated and deallocated at a considerable rate.
   In an attempt to improve the speed of function calls, we maintain
   a separate free list of stack frames (just like floats are
   allocated in a special way -- see floatobject.c).  When a stack
   frame is on the free list, only the following members have a meaning:
    ob_type             == &Frametype
    f_back              next item on free list, or NULL
*/

/* max value for numfree */
#define PyFrame_MAXFREELIST 200

static void _Py_HOT_FUNCTION
frame_dealloc(PyFrameObject *f)
{
    if (_PyObject_GC_IS_TRACKED(f)) {
        _PyObject_GC_UNTRACK(f);
    }

    Py_TRASHCAN_SAFE_BEGIN(f)
    PyCodeObject *co = f->f_code;

    /* Kill all local variables */
    if (f->f_localsptr) {
        for (int i = 0; i < co->co_nlocalsplus+FRAME_SPECIALS_SIZE; i++) {
            Py_CLEAR(f->f_localsptr[i]);
        }
        /* Free items on stack */
        for (int i = 0; i < f->f_stackdepth; i++) {
            Py_XDECREF(f->f_valuestack[i]);
        }
        if (f->f_own_locals_memory) {
            PyMem_Free(f->f_localsptr);
            f->f_own_locals_memory = 0;
        }
    }
    f->f_stackdepth = 0;
    Py_XDECREF(f->f_back);
    Py_CLEAR(f->f_trace);
    struct _Py_frame_state *state = get_frame_state();
#ifdef Py_DEBUG
    // frame_dealloc() must not be called after _PyFrame_Fini()
    assert(state->numfree != -1);
#endif
    if (state->numfree < PyFrame_MAXFREELIST) {
        ++state->numfree;
        f->f_back = state->free_list;
        state->free_list = f;
    }
    else {
        PyObject_GC_Del(f);
    }

    Py_DECREF(co);
    Py_TRASHCAN_SAFE_END(f)
}

static inline Py_ssize_t
frame_nslots(PyFrameObject *frame)
{
    return frame->f_valuestack - frame->f_localsptr;
}

static int
frame_traverse(PyFrameObject *f, visitproc visit, void *arg)
{
    Py_VISIT(f->f_back);
    Py_VISIT(f->f_trace);

    /* locals */
    PyObject **fastlocals = f->f_localsptr;
    for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++fastlocals) {
        Py_VISIT(*fastlocals);
    }

    /* stack */
    for (int i = 0; i < f->f_stackdepth; i++) {
        Py_VISIT(f->f_valuestack[i]);
    }
    return 0;
}

static int
frame_tp_clear(PyFrameObject *f)
{
    /* Before anything else, make sure that this frame is clearly marked
     * as being defunct!  Else, e.g., a generator reachable from this
     * frame may also point to this frame, believe itself to still be
     * active, and try cleaning up this frame again.
     */
    f->f_state = FRAME_CLEARED;

    Py_CLEAR(f->f_trace);

    /* locals */
    PyObject **fastlocals = f->f_localsptr;
    for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++fastlocals) {
        Py_CLEAR(*fastlocals);
    }

    /* stack */
    for (int i = 0; i < f->f_stackdepth; i++) {
        Py_CLEAR(f->f_valuestack[i]);
    }
    f->f_stackdepth = 0;
    return 0;
}

static PyObject *
frame_clear(PyFrameObject *f, PyObject *Py_UNUSED(ignored))
{
    if (_PyFrame_IsExecuting(f)) {
        PyErr_SetString(PyExc_RuntimeError,
                        "cannot clear an executing frame");
        return NULL;
    }
    if (f->f_gen) {
        _PyGen_Finalize(f->f_gen);
        assert(f->f_gen == NULL);
    }
    (void)frame_tp_clear(f);
    Py_RETURN_NONE;
}

PyDoc_STRVAR(clear__doc__,
"F.clear(): clear most references held by the frame");

static PyObject *
frame_sizeof(PyFrameObject *f, PyObject *Py_UNUSED(ignored))
{
    Py_ssize_t res;
    res = sizeof(PyFrameObject);
    if (f->f_own_locals_memory) {
        PyCodeObject *code = f->f_code;
        res += (code->co_nlocalsplus+code->co_stacksize) * sizeof(PyObject *);
    }
    return PyLong_FromSsize_t(res);
}

PyDoc_STRVAR(sizeof__doc__,
"F.__sizeof__() -> size of F in memory, in bytes");

static PyObject *
frame_repr(PyFrameObject *f)
{
    int lineno = PyFrame_GetLineNumber(f);
    PyCodeObject *code = f->f_code;
    return PyUnicode_FromFormat(
        "<frame at %p, file %R, line %d, code %S>",
        f, code->co_filename, lineno, code->co_name);
}

static PyMethodDef frame_methods[] = {
    {"clear",           (PyCFunction)frame_clear,       METH_NOARGS,
     clear__doc__},
    {"__sizeof__",      (PyCFunction)frame_sizeof,      METH_NOARGS,
     sizeof__doc__},
    {NULL,              NULL}   /* sentinel */
};

PyTypeObject PyFrame_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "frame",
    sizeof(PyFrameObject),
    sizeof(PyObject *),
    (destructor)frame_dealloc,                  /* tp_dealloc */
    0,                                          /* tp_vectorcall_offset */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_as_async */
    (reprfunc)frame_repr,                       /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    PyObject_GenericSetAttr,                    /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)frame_traverse,               /* tp_traverse */
    (inquiry)frame_tp_clear,                    /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    0,                                          /* tp_iter */
    0,                                          /* tp_iternext */
    frame_methods,                              /* tp_methods */
    frame_memberlist,                           /* tp_members */
    frame_getsetlist,                           /* tp_getset */
    0,                                          /* tp_base */
    0,                                          /* tp_dict */
};

_Py_IDENTIFIER(__builtins__);

static inline PyFrameObject*
frame_alloc(PyCodeObject *code, PyObject **localsarray)
{
    int owns;
    PyFrameObject *f;
    if (localsarray == NULL) {
        int size = code->co_nlocalsplus+code->co_stacksize + FRAME_SPECIALS_SIZE;
        localsarray = PyMem_Malloc(sizeof(PyObject *)*size);
        if (localsarray == NULL) {
            PyErr_NoMemory();
            return NULL;
        }
        for (Py_ssize_t i=0; i < code->co_nlocalsplus; i++) {
            localsarray[i] = NULL;
        }
        owns = 1;
    }
    else {
        owns = 0;
    }
    struct _Py_frame_state *state = get_frame_state();
    if (state->free_list == NULL)
    {
        f = PyObject_GC_New(PyFrameObject, &PyFrame_Type);
        if (f == NULL) {
            if (owns) {
                PyMem_Free(localsarray);
            }
            return NULL;
        }
    }
    else {
#ifdef Py_DEBUG
        // frame_alloc() must not be called after _PyFrame_Fini()
        assert(state->numfree != -1);
#endif
        assert(state->numfree > 0);
        --state->numfree;
        f = state->free_list;
        state->free_list = state->free_list->f_back;
        _Py_NewReference((PyObject *)f);
    }
    f->f_localsptr = localsarray;
    f->f_own_locals_memory = owns;
    return f;
}

int
_PyFrame_TakeLocals(PyFrameObject *f)
{
    assert(f->f_own_locals_memory == 0);
    assert(f->f_stackdepth == 0);
    Py_ssize_t size = frame_nslots(f);
    PyObject **copy = PyMem_Malloc(sizeof(PyObject *)*size);
    if (copy == NULL) {
        for (int i = 0; i < size; i++) {
            PyObject *o = f->f_localsptr[i];
            Py_XDECREF(o);
        }
        PyErr_NoMemory();
        return -1;
    }
    for (int i = 0; i < size; i++) {
        PyObject *o = f->f_localsptr[i];
        copy[i] = o;
    }
    f->f_own_locals_memory = 1;
    f->f_localsptr = copy;
    f->f_valuestack = copy + size;
    return 0;
}

PyFrameObject* _Py_HOT_FUNCTION
_PyFrame_New_NoTrack(PyThreadState *tstate, PyFrameConstructor *con, PyObject *locals, PyObject **localsarray)
{
    assert(con != NULL);
    assert(con->fc_globals != NULL);
    assert(con->fc_builtins != NULL);
    assert(con->fc_code != NULL);
    assert(locals == NULL || PyMapping_Check(locals));
    PyCodeObject *code = (PyCodeObject *)con->fc_code;

    PyFrameObject *f = frame_alloc(code, localsarray);
    if (f == NULL) {
        return NULL;
    }

    PyObject **specials = f->f_localsptr + code->co_nlocalsplus;
    f->f_valuestack = specials + FRAME_SPECIALS_SIZE;
    f->f_back = (PyFrameObject*)Py_XNewRef(tstate->frame);
    f->f_code = (PyCodeObject *)Py_NewRef(con->fc_code);
    specials[FRAME_SPECIALS_BUILTINS_OFFSET] = Py_NewRef(con->fc_builtins);
    specials[FRAME_SPECIALS_GLOBALS_OFFSET] = Py_NewRef(con->fc_globals);
    specials[FRAME_SPECIALS_LOCALS_OFFSET] = Py_XNewRef(locals);
    f->f_trace = NULL;
    f->f_stackdepth = 0;
    f->f_trace_lines = 1;
    f->f_trace_opcodes = 0;
    f->f_gen = NULL;
    f->f_lasti = -1;
    f->f_lineno = 0;
    f->f_state = FRAME_CREATED;
    return f;
}

/* Legacy API */
PyFrameObject*
PyFrame_New(PyThreadState *tstate, PyCodeObject *code,
            PyObject *globals, PyObject *locals)
{
    PyObject *builtins = _PyEval_BuiltinsFromGlobals(tstate, globals); // borrowed ref
    if (builtins == NULL) {
        return NULL;
    }
    PyFrameConstructor desc = {
        .fc_globals = globals,
        .fc_builtins = builtins,
        .fc_name = code->co_name,
        .fc_qualname = code->co_name,
        .fc_code = (PyObject *)code,
        .fc_defaults = NULL,
        .fc_kwdefaults = NULL,
        .fc_closure = NULL
    };
    PyFrameObject *f = _PyFrame_New_NoTrack(tstate, &desc, locals, NULL);
    if (f) {
        _PyObject_GC_TRACK(f);
    }
    return f;
}

/* Convert between "fast" version of locals and dictionary version.

   map and values are input arguments.  map is a tuple of strings.
   values is an array of PyObject*.  At index i, map[i] is the name of
   the variable with value values[i].  The function copies the first
   nmap variable from map/values into dict.  If values[i] is NULL,
   the variable is deleted from dict.

   If deref is true, then the values being copied are cell variables
   and the value is extracted from the cell variable before being put
   in dict.
 */

static int
map_to_dict(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
            int deref)
{
    Py_ssize_t j;
    assert(PyTuple_Check(map));
    assert(PyDict_Check(dict));
    assert(PyTuple_Size(map) >= nmap);
    for (j=0; j < nmap; j++) {
        PyObject *key = PyTuple_GET_ITEM(map, j);
        PyObject *value = values[j];
        assert(PyUnicode_Check(key));
        if (deref && value != NULL) {
            assert(PyCell_Check(value));
            value = PyCell_GET(value);
        }
        if (value == NULL) {
            if (PyObject_DelItem(dict, key) != 0) {
                if (PyErr_ExceptionMatches(PyExc_KeyError))
                    PyErr_Clear();
                else
                    return -1;
            }
        }
        else {
            if (PyObject_SetItem(dict, key, value) != 0)
                return -1;
        }
    }
    return 0;
}

/* Copy values from the "locals" dict into the fast locals.

   dict is an input argument containing string keys representing
   variables names and arbitrary PyObject* as values.

   map and values are input arguments.  map is a tuple of strings.
   values is an array of PyObject*.  At index i, map[i] is the name of
   the variable with value values[i].  The function copies the first
   nmap variable from map/values into dict.  If values[i] is NULL,
   the variable is deleted from dict.

   If deref is true, then the values being copied are cell variables
   and the value is extracted from the cell variable before being put
   in dict.  If clear is true, then variables in map but not in dict
   are set to NULL in map; if clear is false, variables missing in
   dict are ignored.

   Exceptions raised while modifying the dict are silently ignored,
   because there is no good way to report them.
*/

static void
dict_to_map(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
            int deref, int clear)
{
    Py_ssize_t j;
    assert(PyTuple_Check(map));
    assert(PyDict_Check(dict));
    assert(PyTuple_Size(map) >= nmap);
    for (j=0; j < nmap; j++) {
        PyObject *key = PyTuple_GET_ITEM(map, j);
        PyObject *value = PyObject_GetItem(dict, key);
        assert(PyUnicode_Check(key));
        /* We only care about NULLs if clear is true. */
        if (value == NULL) {
            PyErr_Clear();
            if (!clear)
                continue;
        }
        if (deref) {
            assert(PyCell_Check(values[j]));
            if (PyCell_GET(values[j]) != value) {
                if (PyCell_Set(values[j], value) < 0)
                    PyErr_Clear();
            }
        } else if (values[j] != value) {
            Py_XINCREF(value);
            Py_XSETREF(values[j], value);
        }
        Py_XDECREF(value);
    }
}

int
PyFrame_FastToLocalsWithError(PyFrameObject *f)
{
    /* Merge fast locals into f->f_locals */
    PyObject *locals, *map;
    PyObject **fast;
    PyCodeObject *co;
    Py_ssize_t j;

    if (f == NULL) {
        PyErr_BadInternalCall();
        return -1;
    }
    locals = _PyFrame_Specials(f)[FRAME_SPECIALS_LOCALS_OFFSET];
    if (locals == NULL) {
        locals = _PyFrame_Specials(f)[FRAME_SPECIALS_LOCALS_OFFSET] = PyDict_New();
        if (locals == NULL)
            return -1;
    }
    co = f->f_code;
    map = co->co_varnames;
    if (!PyTuple_Check(map)) {
        PyErr_Format(PyExc_SystemError,
                     "co_varnames must be a tuple, not %s",
                     Py_TYPE(map)->tp_name);
        return -1;
    }
    fast = f->f_localsptr;
    j = PyTuple_GET_SIZE(map);
    if (j > co->co_nlocals)
        j = co->co_nlocals;
    if (co->co_nlocals) {
        if (map_to_dict(map, j, locals, fast, 0) < 0)
            return -1;
    }
    if (co->co_ncellvars || co->co_nfreevars) {
        if (map_to_dict(co->co_cellvars, co->co_ncellvars,
                        locals, fast + co->co_nlocals, 1))
            return -1;

        /* If the namespace is unoptimized, then one of the
           following cases applies:
           1. It does not contain free variables, because it
              uses import * or is a top-level namespace.
           2. It is a class namespace.
           We don't want to accidentally copy free variables
           into the locals dict used by the class.
        */
        if (co->co_flags & CO_OPTIMIZED) {
            if (map_to_dict(co->co_freevars, co->co_nfreevars, locals,
                            fast + co->co_nlocals + co->co_ncellvars, 1) < 0)
                return -1;
        }
    }
    return 0;
}

void
PyFrame_FastToLocals(PyFrameObject *f)
{
    int res;

    assert(!PyErr_Occurred());

    res = PyFrame_FastToLocalsWithError(f);
    if (res < 0)
        PyErr_Clear();
}

void
PyFrame_LocalsToFast(PyFrameObject *f, int clear)
{
    /* Merge locals into fast locals */
    PyObject *locals, *map;
    PyObject **fast;
    PyObject *error_type, *error_value, *error_traceback;
    PyCodeObject *co;
    Py_ssize_t j;
    if (f == NULL)
        return;
    locals = _PyFrame_Specials(f)[FRAME_SPECIALS_LOCALS_OFFSET];
    co = f->f_code;
    map = co->co_varnames;
    if (locals == NULL)
        return;
    if (!PyTuple_Check(map))
        return;
    PyErr_Fetch(&error_type, &error_value, &error_traceback);
    fast = f->f_localsptr;
    j = PyTuple_GET_SIZE(map);
    if (j > co->co_nlocals)
        j = co->co_nlocals;
    if (co->co_nlocals)
        dict_to_map(co->co_varnames, j, locals, fast, 0, clear);
    if (co->co_ncellvars || co->co_nfreevars) {
        dict_to_map(co->co_cellvars, co->co_ncellvars,
                    locals, fast + co->co_nlocals, 1, clear);
        /* Same test as in PyFrame_FastToLocals() above. */
        if (co->co_flags & CO_OPTIMIZED) {
            dict_to_map(co->co_freevars, co->co_nfreevars, locals,
                        fast + co->co_nlocals + co->co_ncellvars, 1,
                        clear);
        }
    }
    PyErr_Restore(error_type, error_value, error_traceback);
}

/* Clear out the free list */
void
_PyFrame_ClearFreeList(PyInterpreterState *interp)
{
    struct _Py_frame_state *state = &interp->frame;
    while (state->free_list != NULL) {
        PyFrameObject *f = state->free_list;
        state->free_list = state->free_list->f_back;
        PyObject_GC_Del(f);
        --state->numfree;
    }
    assert(state->numfree == 0);
}

void
_PyFrame_Fini(PyInterpreterState *interp)
{
    _PyFrame_ClearFreeList(interp);
#ifdef Py_DEBUG
    struct _Py_frame_state *state = &interp->frame;
    state->numfree = -1;
#endif
}

/* Print summary info about the state of the optimized allocator */
void
_PyFrame_DebugMallocStats(FILE *out)
{
    struct _Py_frame_state *state = get_frame_state();
    _PyDebugAllocatorStats(out,
                           "free PyFrameObject",
                           state->numfree, sizeof(PyFrameObject));
}


PyCodeObject *
PyFrame_GetCode(PyFrameObject *frame)
{
    assert(frame != NULL);
    PyCodeObject *code = frame->f_code;
    assert(code != NULL);
    Py_INCREF(code);
    return code;
}


PyFrameObject*
PyFrame_GetBack(PyFrameObject *frame)
{
    assert(frame != NULL);
    PyFrameObject *back = frame->f_back;
    Py_XINCREF(back);
    return back;
}

PyObject*
_PyEval_BuiltinsFromGlobals(PyThreadState *tstate, PyObject *globals)
{
    PyObject *builtins = _PyDict_GetItemIdWithError(globals, &PyId___builtins__);
    if (builtins) {
        if (PyModule_Check(builtins)) {
            builtins = _PyModule_GetDict(builtins);
            assert(builtins != NULL);
        }
        return builtins;
    }
    if (PyErr_Occurred()) {
        return NULL;
    }

    return _PyEval_GetBuiltins(tstate);
}