ceval.c

/* Execute compiled code */

/* XXX TO DO:
   XXX speed up searching for keywords by using a dictionary
   XXX document it!
   */

/* enable more aggressive intra-module optimizations, where available */
#define PY_LOCAL_AGGRESSIVE

#include "Python.h"

#include "code.h"
#include "frameobject.h"
#include "eval.h"
#include "opcode.h"
#include "structmember.h"

#include <ctype.h>

#ifndef WITH_TSC

#define READ_TIMESTAMP(var)

#else

typedef unsigned long long uint64;

#if defined(__ppc__) /* <- Don't know if this is the correct symbol; this
                           section should work for GCC on any PowerPC
                           platform, irrespective of OS.
                           POWER?  Who knows :-) */

#define READ_TIMESTAMP(var) ppc_getcounter(&var)

static void
ppc_getcounter(uint64 *v)
{
    register unsigned long tbu, tb, tbu2;

  loop:
    asm volatile ("mftbu %0" : "=r" (tbu) );
    asm volatile ("mftb  %0" : "=r" (tb)  );
    asm volatile ("mftbu %0" : "=r" (tbu2));
    if (__builtin_expect(tbu != tbu2, 0)) goto loop;

    /* The slightly peculiar way of writing the next lines is
       compiled better by GCC than any other way I tried. */
    ((long*)(v))[0] = tbu;
    ((long*)(v))[1] = tb;
}

#elif defined(__i386__)

/* this is for linux/x86 (and probably any other GCC/x86 combo) */

#define READ_TIMESTAMP(val) \
     __asm__ __volatile__("rdtsc" : "=A" (val))

#elif defined(__x86_64__)

/* for gcc/x86_64, the "A" constraint in DI mode means *either* rax *or* rdx;
   not edx:eax as it does for i386.  Since rdtsc puts its result in edx:eax
   even in 64-bit mode, we need to use "a" and "d" for the lower and upper
   32-bit pieces of the result. */

#define READ_TIMESTAMP(val) \
    __asm__ __volatile__("rdtsc" : \
                         "=a" (((int*)&(val))[0]), "=d" (((int*)&(val))[1]));


#else

#error "Don't know how to implement timestamp counter for this architecture"

#endif

void dump_tsc(int opcode, int ticked, uint64 inst0, uint64 inst1,
              uint64 loop0, uint64 loop1, uint64 intr0, uint64 intr1)
{
    uint64 intr, inst, loop;
    PyThreadState *tstate = PyThreadState_Get();
    if (!tstate->interp->tscdump)
        return;
    intr = intr1 - intr0;
    inst = inst1 - inst0 - intr;
    loop = loop1 - loop0 - intr;
    fprintf(stderr, "opcode=%03d t=%d inst=%06lld loop=%06lld\n",
            opcode, ticked, inst, loop);
}

#endif

/* Turn this on if your compiler chokes on the big switch: */
/* #define CASE_TOO_BIG 1 */

#ifdef Py_DEBUG
/* For debugging the interpreter: */
#define LLTRACE  1      /* Low-level trace feature */
#define CHECKEXC 1      /* Double-check exception checking */
#endif

typedef PyObject *(*callproc)(PyObject *, PyObject *, PyObject *);

/* Forward declarations */
#ifdef WITH_TSC
static PyObject * call_function(PyObject ***, int, uint64*, uint64*);
#else
static PyObject * call_function(PyObject ***, int);
#endif
static PyObject * fast_function(PyObject *, PyObject ***, int, int, int);
static PyObject * do_call(PyObject *, PyObject ***, int, int);
static PyObject * ext_do_call(PyObject *, PyObject ***, int, int, int);
static PyObject * update_keyword_args(PyObject *, int, PyObject ***,
                                      PyObject *);
static PyObject * update_star_args(int, int, PyObject *, PyObject ***);
static PyObject * load_args(PyObject ***, int);
#define CALL_FLAG_VAR 1
#define CALL_FLAG_KW 2

#ifdef LLTRACE
static int lltrace;
static int prtrace(PyObject *, char *);
#endif
static int call_trace(Py_tracefunc, PyObject *, PyFrameObject *,
                      int, PyObject *);
static int call_trace_protected(Py_tracefunc, PyObject *,
                                PyFrameObject *, int, PyObject *);
static void call_exc_trace(Py_tracefunc, PyObject *, PyFrameObject *);
static int maybe_call_line_trace(Py_tracefunc, PyObject *,
                                 PyFrameObject *, int *, int *, int *);

static PyObject * apply_slice(PyObject *, PyObject *, PyObject *);
static int assign_slice(PyObject *, PyObject *,
                        PyObject *, PyObject *);
static PyObject * cmp_outcome(int, PyObject *, PyObject *);
static PyObject * import_from(PyObject *, PyObject *);
static int import_all_from(PyObject *, PyObject *);
static PyObject * build_class(PyObject *, PyObject *, PyObject *);
static int exec_statement(PyFrameObject *,
                          PyObject *, PyObject *, PyObject *);
static void set_exc_info(PyThreadState *, PyObject *, PyObject *, PyObject *);
static void reset_exc_info(PyThreadState *);
static void format_exc_check_arg(PyObject *, char *, PyObject *);
static PyObject * string_concatenate(PyObject *, PyObject *,
                                     PyFrameObject *, unsigned char *);
static PyObject * kwd_as_string(PyObject *);

#define NAME_ERROR_MSG \
    "name '%.200s' is not defined"
#define GLOBAL_NAME_ERROR_MSG \
    "global name '%.200s' is not defined"
#define UNBOUNDLOCAL_ERROR_MSG \
    "local variable '%.200s' referenced before assignment"
#define UNBOUNDFREE_ERROR_MSG \
    "free variable '%.200s' referenced before assignment" \
    " in enclosing scope"

/* Dynamic execution profile */
#ifdef DYNAMIC_EXECUTION_PROFILE
#ifdef DXPAIRS
static long dxpairs[257][256];
#define dxp dxpairs[256]
#else
static long dxp[256];
#endif
#endif

/* Function call profile */
#ifdef CALL_PROFILE
#define PCALL_NUM 11
static int pcall[PCALL_NUM];

#define PCALL_ALL 0
#define PCALL_FUNCTION 1
#define PCALL_FAST_FUNCTION 2
#define PCALL_FASTER_FUNCTION 3
#define PCALL_METHOD 4
#define PCALL_BOUND_METHOD 5
#define PCALL_CFUNCTION 6
#define PCALL_TYPE 7
#define PCALL_GENERATOR 8
#define PCALL_OTHER 9
#define PCALL_POP 10

/* Notes about the statistics

   PCALL_FAST stats

   FAST_FUNCTION means no argument tuple needs to be created.
   FASTER_FUNCTION means that the fast-path frame setup code is used.

   If there is a method call where the call can be optimized by changing
   the argument tuple and calling the function directly, it gets recorded
   twice.

   As a result, the relationship among the statistics appears to be
   PCALL_ALL == PCALL_FUNCTION + PCALL_METHOD - PCALL_BOUND_METHOD +
                PCALL_CFUNCTION + PCALL_TYPE + PCALL_GENERATOR + PCALL_OTHER
   PCALL_FUNCTION > PCALL_FAST_FUNCTION > PCALL_FASTER_FUNCTION
   PCALL_METHOD > PCALL_BOUND_METHOD
*/

#define PCALL(POS) pcall[POS]++

PyObject *
PyEval_GetCallStats(PyObject *self)
{
    return Py_BuildValue("iiiiiiiiiii",
                         pcall[0], pcall[1], pcall[2], pcall[3],
                         pcall[4], pcall[5], pcall[6], pcall[7],
                         pcall[8], pcall[9], pcall[10]);
}
#else
#define PCALL(O)

PyObject *
PyEval_GetCallStats(PyObject *self)
{
    Py_INCREF(Py_None);
    return Py_None;
}
#endif


#ifdef WITH_THREAD

#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#include "pythread.h"

static PyThread_type_lock interpreter_lock = 0; /* This is the GIL */
static long main_thread = 0;

int
PyEval_ThreadsInitialized(void)
{
    return interpreter_lock != 0;
}

void
PyEval_InitThreads(void)
{
    if (interpreter_lock)
        return;
    interpreter_lock = PyThread_allocate_lock();
    PyThread_acquire_lock(interpreter_lock, 1);
    main_thread = PyThread_get_thread_ident();
}

void
PyEval_AcquireLock(void)
{
    PyThread_acquire_lock(interpreter_lock, 1);
}

void
PyEval_ReleaseLock(void)
{
    PyThread_release_lock(interpreter_lock);
}

void
PyEval_AcquireThread(PyThreadState *tstate)
{
    if (tstate == NULL)
        Py_FatalError("PyEval_AcquireThread: NULL new thread state");
    /* Check someone has called PyEval_InitThreads() to create the lock */
    assert(interpreter_lock);
    PyThread_acquire_lock(interpreter_lock, 1);
    if (PyThreadState_Swap(tstate) != NULL)
        Py_FatalError(
            "PyEval_AcquireThread: non-NULL old thread state");
}

void
PyEval_ReleaseThread(PyThreadState *tstate)
{
    if (tstate == NULL)
        Py_FatalError("PyEval_ReleaseThread: NULL thread state");
    if (PyThreadState_Swap(NULL) != tstate)
        Py_FatalError("PyEval_ReleaseThread: wrong thread state");
    PyThread_release_lock(interpreter_lock);
}

/* This function is called from PyOS_AfterFork to ensure that newly
   created child processes don't hold locks referring to threads which
   are not running in the child process.  (This could also be done using
   pthread_atfork mechanism, at least for the pthreads implementation.) */

void
PyEval_ReInitThreads(void)
{
    PyObject *threading, *result;
    PyThreadState *tstate;

    if (!interpreter_lock)
        return;
    /*XXX Can't use PyThread_free_lock here because it does too
      much error-checking.  Doing this cleanly would require
      adding a new function to each thread_*.h.  Instead, just
      create a new lock and waste a little bit of memory */
    interpreter_lock = PyThread_allocate_lock();
    PyThread_acquire_lock(interpreter_lock, 1);
    main_thread = PyThread_get_thread_ident();

    /* Update the threading module with the new state.
     */
    tstate = PyThreadState_GET();
    threading = PyMapping_GetItemString(tstate->interp->modules,
                                        "threading");
    if (threading == NULL) {
        /* threading not imported */
        PyErr_Clear();
        return;
    }
    result = PyObject_CallMethod(threading, "_after_fork", NULL);
    if (result == NULL)
        PyErr_WriteUnraisable(threading);
    else
        Py_DECREF(result);
    Py_DECREF(threading);
}
#endif

/* Functions save_thread and restore_thread are always defined so
   dynamically loaded modules needn't be compiled separately for use
   with and without threads: */

PyThreadState *
PyEval_SaveThread(void)
{
    PyThreadState *tstate = PyThreadState_Swap(NULL);
    if (tstate == NULL)
        Py_FatalError("PyEval_SaveThread: NULL tstate");
#ifdef WITH_THREAD
    if (interpreter_lock)
        PyThread_release_lock(interpreter_lock);
#endif
    return tstate;
}

void
PyEval_RestoreThread(PyThreadState *tstate)
{
    if (tstate == NULL)
        Py_FatalError("PyEval_RestoreThread: NULL tstate");
#ifdef WITH_THREAD
    if (interpreter_lock) {
        int err = errno;
        PyThread_acquire_lock(interpreter_lock, 1);
        errno = err;
    }
#endif
    PyThreadState_Swap(tstate);
}


/* Mechanism whereby asynchronously executing callbacks (e.g. UNIX
   signal handlers or Mac I/O completion routines) can schedule calls
   to a function to be called synchronously.
   The synchronous function is called with one void* argument.
   It should return 0 for success or -1 for failure -- failure should
   be accompanied by an exception.

   If registry succeeds, the registry function returns 0; if it fails
   (e.g. due to too many pending calls) it returns -1 (without setting
   an exception condition).

   Note that because registry may occur from within signal handlers,
   or other asynchronous events, calling malloc() is unsafe!

#ifdef WITH_THREAD
   Any thread can schedule pending calls, but only the main thread
   will execute them.
#endif

   XXX WARNING!  ASYNCHRONOUSLY EXECUTING CODE!
   There are two possible race conditions:
   (1) nested asynchronous registry calls;
   (2) registry calls made while pending calls are being processed.
   While (1) is very unlikely, (2) is a real possibility.
   The current code is safe against (2), but not against (1).
   The safety against (2) is derived from the fact that only one
   thread (the main thread) ever takes things out of the queue.

   XXX Darn!  With the advent of thread state, we should have an array
   of pending calls per thread in the thread state!  Later...
*/

#define NPENDINGCALLS 32
static struct {
    int (*func)(void *);
    void *arg;
} pendingcalls[NPENDINGCALLS];
static volatile int pendingfirst = 0;
static volatile int pendinglast = 0;
static volatile int things_to_do = 0;

int
Py_AddPendingCall(int (*func)(void *), void *arg)
{
    static volatile int busy = 0;
    int i, j;
    /* XXX Begin critical section */
    /* XXX If you want this to be safe against nested
       XXX asynchronous calls, you'll have to work harder! */
    if (busy)
        return -1;
    busy = 1;
    i = pendinglast;
    j = (i + 1) % NPENDINGCALLS;
    if (j == pendingfirst) {
        busy = 0;
        return -1; /* Queue full */
    }
    pendingcalls[i].func = func;
    pendingcalls[i].arg = arg;
    pendinglast = j;

    _Py_Ticker = 0;
    things_to_do = 1; /* Signal main loop */
    busy = 0;
    /* XXX End critical section */
    return 0;
}

int
Py_MakePendingCalls(void)
{
    static int busy = 0;
#ifdef WITH_THREAD
    if (main_thread && PyThread_get_thread_ident() != main_thread)
        return 0;
#endif
    if (busy)
        return 0;
    busy = 1;
    things_to_do = 0;
    for (;;) {
        int i;
        int (*func)(void *);
        void *arg;
        i = pendingfirst;
        if (i == pendinglast)
            break; /* Queue empty */
        func = pendingcalls[i].func;
        arg = pendingcalls[i].arg;
        pendingfirst = (i + 1) % NPENDINGCALLS;
        if (func(arg) < 0) {
            busy = 0;
            things_to_do = 1; /* We're not done yet */
            return -1;
        }
    }
    busy = 0;
    return 0;
}


/* The interpreter's recursion limit */

#ifndef Py_DEFAULT_RECURSION_LIMIT
#define Py_DEFAULT_RECURSION_LIMIT 1000
#endif
static int recursion_limit = Py_DEFAULT_RECURSION_LIMIT;
int _Py_CheckRecursionLimit = Py_DEFAULT_RECURSION_LIMIT;

int
Py_GetRecursionLimit(void)
{
    return recursion_limit;
}

void
Py_SetRecursionLimit(int new_limit)
{
    recursion_limit = new_limit;
    _Py_CheckRecursionLimit = recursion_limit;
}

/* the macro Py_EnterRecursiveCall() only calls _Py_CheckRecursiveCall()
   if the recursion_depth reaches _Py_CheckRecursionLimit.
   If USE_STACKCHECK, the macro decrements _Py_CheckRecursionLimit
   to guarantee that _Py_CheckRecursiveCall() is regularly called.
   Without USE_STACKCHECK, there is no need for this. */
int
_Py_CheckRecursiveCall(char *where)
{
    PyThreadState *tstate = PyThreadState_GET();

#ifdef USE_STACKCHECK
    if (PyOS_CheckStack()) {
        --tstate->recursion_depth;
        PyErr_SetString(PyExc_MemoryError, "Stack overflow");
        return -1;
    }
#endif
    if (tstate->recursion_depth > recursion_limit) {
        --tstate->recursion_depth;
        PyErr_Format(PyExc_RuntimeError,
                     "maximum recursion depth exceeded%s",
                     where);
        return -1;
    }
    _Py_CheckRecursionLimit = recursion_limit;
    return 0;
}

/* Status code for main loop (reason for stack unwind) */
enum why_code {
        WHY_NOT =       0x0001, /* No error */
        WHY_EXCEPTION = 0x0002, /* Exception occurred */
        WHY_RERAISE =   0x0004, /* Exception re-raised by 'finally' */
        WHY_RETURN =    0x0008, /* 'return' statement */
        WHY_BREAK =     0x0010, /* 'break' statement */
        WHY_CONTINUE =  0x0020, /* 'continue' statement */
        WHY_YIELD =     0x0040  /* 'yield' operator */
};

static enum why_code do_raise(PyObject *, PyObject *, PyObject *);
static int unpack_iterable(PyObject *, int, PyObject **);

/* Records whether tracing is on for any thread.  Counts the number of
   threads for which tstate->c_tracefunc is non-NULL, so if the value
   is 0, we know we don't have to check this thread's c_tracefunc.
   This speeds up the if statement in PyEval_EvalFrameEx() after
   fast_next_opcode*/
static int _Py_TracingPossible = 0;

/* for manipulating the thread switch and periodic "stuff" - used to be
   per thread, now just a pair o' globals */
int _Py_CheckInterval = 100;
volatile int _Py_Ticker = 100;

PyObject *
PyEval_EvalCode(PyCodeObject *co, PyObject *globals, PyObject *locals)
{
    return PyEval_EvalCodeEx(co,
                      globals, locals,
                      (PyObject **)NULL, 0,
                      (PyObject **)NULL, 0,
                      (PyObject **)NULL, 0,
                      NULL);
}


/* Interpreter main loop */

PyObject *
PyEval_EvalFrame(PyFrameObject *f) {
    /* This is for backward compatibility with extension modules that
       used this API; core interpreter code should call
       PyEval_EvalFrameEx() */
    return PyEval_EvalFrameEx(f, 0);
}

PyObject *
PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
{
#ifdef DXPAIRS
    int lastopcode = 0;
#endif
    register PyObject **stack_pointer;  /* Next free slot in value stack */
    register unsigned char *next_instr;
    register int opcode;        /* Current opcode */
    register int oparg;         /* Current opcode argument, if any */
    register enum why_code why; /* Reason for block stack unwind */
    register int err;           /* Error status -- nonzero if error */
    register PyObject *x;       /* Result object -- NULL if error */
    register PyObject *v;       /* Temporary objects popped off stack */
    register PyObject *w;
    register PyObject *u;
    register PyObject *t;
    register PyObject *stream = NULL;    /* for PRINT opcodes */
    register PyObject **fastlocals, **freevars;
    PyObject *retval = NULL;            /* Return value */
    PyThreadState *tstate = PyThreadState_GET();
    PyCodeObject *co;

    /* when tracing we set things up so that

           not (instr_lb <= current_bytecode_offset < instr_ub)

       is true when the line being executed has changed.  The
       initial values are such as to make this false the first
       time it is tested. */
    int instr_ub = -1, instr_lb = 0, instr_prev = -1;

    unsigned char *first_instr;
    PyObject *names;
    PyObject *consts;
#if defined(Py_DEBUG) || defined(LLTRACE)
    /* Make it easier to find out where we are with a debugger */
    char *filename;
#endif

/* Tuple access macros */

#ifndef Py_DEBUG
#define GETITEM(v, i) PyTuple_GET_ITEM((PyTupleObject *)(v), (i))
#else
#define GETITEM(v, i) PyTuple_GetItem((v), (i))
#endif

#ifdef WITH_TSC
/* Use Pentium timestamp counter to mark certain events:
   inst0 -- beginning of switch statement for opcode dispatch
   inst1 -- end of switch statement (may be skipped)
   loop0 -- the top of the mainloop
   loop1 -- place where control returns again to top of mainloop
            (may be skipped)
   intr1 -- beginning of long interruption
   intr2 -- end of long interruption

   Many opcodes call out to helper C functions.  In some cases, the
   time in those functions should be counted towards the time for the
   opcode, but not in all cases.  For example, a CALL_FUNCTION opcode
   calls another Python function; there's no point in charge all the
   bytecode executed by the called function to the caller.

   It's hard to make a useful judgement statically.  In the presence
   of operator overloading, it's impossible to tell if a call will
   execute new Python code or not.

   It's a case-by-case judgement.  I'll use intr1 for the following
   cases:

   EXEC_STMT
   IMPORT_STAR
   IMPORT_FROM
   CALL_FUNCTION (and friends)

 */
    uint64 inst0, inst1, loop0, loop1, intr0 = 0, intr1 = 0;
    int ticked = 0;

    READ_TIMESTAMP(inst0);
    READ_TIMESTAMP(inst1);
    READ_TIMESTAMP(loop0);
    READ_TIMESTAMP(loop1);

    /* shut up the compiler */
    opcode = 0;
#endif

/* Code access macros */

#define INSTR_OFFSET()  ((int)(next_instr - first_instr))
#define NEXTOP()        (*next_instr++)
#define NEXTARG()       (next_instr += 2, (next_instr[-1]<<8) + next_instr[-2])
#define PEEKARG()       ((next_instr[2]<<8) + next_instr[1])
#define JUMPTO(x)       (next_instr = first_instr + (x))
#define JUMPBY(x)       (next_instr += (x))

/* OpCode prediction macros
    Some opcodes tend to come in pairs thus making it possible to
    predict the second code when the first is run.  For example,
    COMPARE_OP is often followed by JUMP_IF_FALSE or JUMP_IF_TRUE.  And,
    those opcodes are often followed by a POP_TOP.

    Verifying the prediction costs a single high-speed test of a register
    variable against a constant.  If the pairing was good, then the
    processor's own internal branch predication has a high likelihood of
    success, resulting in a nearly zero-overhead transition to the
    next opcode.  A successful prediction saves a trip through the eval-loop
    including its two unpredictable branches, the HAS_ARG test and the
    switch-case.  Combined with the processor's internal branch prediction,
    a successful PREDICT has the effect of making the two opcodes run as if
    they were a single new opcode with the bodies combined.

    If collecting opcode statistics, your choices are to either keep the
    predictions turned-on and interpret the results as if some opcodes
    had been combined or turn-off predictions so that the opcode frequency
    counter updates for both opcodes.
*/

#ifdef DYNAMIC_EXECUTION_PROFILE
#define PREDICT(op)             if (0) goto PRED_##op
#else
#define PREDICT(op)             if (*next_instr == op) goto PRED_##op
#endif

#define PREDICTED(op)           PRED_##op: next_instr++
#define PREDICTED_WITH_ARG(op)  PRED_##op: oparg = PEEKARG(); next_instr += 3

/* Stack manipulation macros */

/* The stack can grow at most MAXINT deep, as co_nlocals and
   co_stacksize are ints. */
#define STACK_LEVEL()     ((int)(stack_pointer - f->f_valuestack))
#define EMPTY()           (STACK_LEVEL() == 0)
#define TOP()             (stack_pointer[-1])
#define SECOND()          (stack_pointer[-2])
#define THIRD()           (stack_pointer[-3])
#define FOURTH()          (stack_pointer[-4])
#define SET_TOP(v)        (stack_pointer[-1] = (v))
#define SET_SECOND(v)     (stack_pointer[-2] = (v))
#define SET_THIRD(v)      (stack_pointer[-3] = (v))
#define SET_FOURTH(v)     (stack_pointer[-4] = (v))
#define BASIC_STACKADJ(n) (stack_pointer += n)
#define BASIC_PUSH(v)     (*stack_pointer++ = (v))
#define BASIC_POP()       (*--stack_pointer)

#ifdef LLTRACE
#define PUSH(v)         { (void)(BASIC_PUSH(v), \
                          lltrace && prtrace(TOP(), "push")); \
                          assert(STACK_LEVEL() <= co->co_stacksize); }
#define POP()           ((void)(lltrace && prtrace(TOP(), "pop")), \
                         BASIC_POP())
#define STACKADJ(n)     { (void)(BASIC_STACKADJ(n), \
                          lltrace && prtrace(TOP(), "stackadj")); \
                          assert(STACK_LEVEL() <= co->co_stacksize); }
#define EXT_POP(STACK_POINTER) ((void)(lltrace && \
                                prtrace((STACK_POINTER)[-1], "ext_pop")), \
                                *--(STACK_POINTER))
#else
#define PUSH(v)                BASIC_PUSH(v)
#define POP()                  BASIC_POP()
#define STACKADJ(n)            BASIC_STACKADJ(n)
#define EXT_POP(STACK_POINTER) (*--(STACK_POINTER))
#endif

/* Local variable macros */

#define GETLOCAL(i)     (fastlocals[i])

/* The SETLOCAL() macro must not DECREF the local variable in-place and
   then store the new value; it must copy the old value to a temporary
   value, then store the new value, and then DECREF the temporary value.
   This is because it is possible that during the DECREF the frame is
   accessed by other code (e.g. a __del__ method or gc.collect()) and the
   variable would be pointing to already-freed memory. */
#define SETLOCAL(i, value)      do { PyObject *tmp = GETLOCAL(i); \
                                     GETLOCAL(i) = value; \
                                     Py_XDECREF(tmp); } while (0)

/* Start of code */

    if (f == NULL)
        return NULL;

    /* push frame */
    if (Py_EnterRecursiveCall(""))
        return NULL;

    tstate->frame = f;

    if (tstate->use_tracing) {
        if (tstate->c_tracefunc != NULL) {
            /* tstate->c_tracefunc, if defined, is a
               function that will be called on *every* entry
               to a code block.  Its return value, if not
               None, is a function that will be called at
               the start of each executed line of code.
               (Actually, the function must return itself
               in order to continue tracing.)  The trace
               functions are called with three arguments:
               a pointer to the current frame, a string
               indicating why the function is called, and
               an argument which depends on the situation.
               The global trace function is also called
               whenever an exception is detected. */
            if (call_trace_protected(tstate->c_tracefunc,
                                     tstate->c_traceobj,
                                     f, PyTrace_CALL, Py_None)) {
                /* Trace function raised an error */
                goto exit_eval_frame;
            }
        }
        if (tstate->c_profilefunc != NULL) {
            /* Similar for c_profilefunc, except it needn't
               return itself and isn't called for "line" events */
            if (call_trace_protected(tstate->c_profilefunc,
                                     tstate->c_profileobj,
                                     f, PyTrace_CALL, Py_None)) {
                /* Profile function raised an error */
                goto exit_eval_frame;
            }
        }
    }

    co = f->f_code;
    names = co->co_names;
    consts = co->co_consts;
    fastlocals = f->f_localsplus;
    freevars = f->f_localsplus + co->co_nlocals;
    first_instr = (unsigned char*) PyString_AS_STRING(co->co_code);
    /* An explanation is in order for the next line.

       f->f_lasti now refers to the index of the last instruction
       executed.  You might think this was obvious from the name, but
       this wasn't always true before 2.3!  PyFrame_New now sets
       f->f_lasti to -1 (i.e. the index *before* the first instruction)
       and YIELD_VALUE doesn't fiddle with f_lasti any more.  So this
       does work.  Promise.

       When the PREDICT() macros are enabled, some opcode pairs follow in
       direct succession without updating f->f_lasti.  A successful
       prediction effectively links the two codes together as if they
       were a single new opcode; accordingly,f->f_lasti will point to
       the first code in the pair (for instance, GET_ITER followed by
       FOR_ITER is effectively a single opcode and f->f_lasti will point
       at to the beginning of the combined pair.)
    */
    next_instr = first_instr + f->f_lasti + 1;
    stack_pointer = f->f_stacktop;
    assert(stack_pointer != NULL);
    f->f_stacktop = NULL;       /* remains NULL unless yield suspends frame */

#ifdef LLTRACE
    lltrace = PyDict_GetItemString(f->f_globals, "__lltrace__") != NULL;
#endif
#if defined(Py_DEBUG) || defined(LLTRACE)
    filename = PyString_AsString(co->co_filename);
#endif

    why = WHY_NOT;
    err = 0;
    x = Py_None;        /* Not a reference, just anything non-NULL */
    w = NULL;

    if (throwflag) { /* support for generator.throw() */
        why = WHY_EXCEPTION;
        goto on_error;
    }

    for (;;) {
#ifdef WITH_TSC
        if (inst1 == 0) {
            /* Almost surely, the opcode executed a break
               or a continue, preventing inst1 from being set
               on the way out of the loop.
            */
            READ_TIMESTAMP(inst1);
            loop1 = inst1;
        }
        dump_tsc(opcode, ticked, inst0, inst1, loop0, loop1,
                 intr0, intr1);
        ticked = 0;
        inst1 = 0;
        intr0 = 0;
        intr1 = 0;
        READ_TIMESTAMP(loop0);
#endif
        assert(stack_pointer >= f->f_valuestack); /* else underflow */
        assert(STACK_LEVEL() <= co->co_stacksize);  /* else overflow */

        /* Do periodic things.  Doing this every time through
           the loop would add too much overhead, so we do it
           only every Nth instruction.  We also do it if
           ``things_to_do'' is set, i.e. when an asynchronous
           event needs attention (e.g. a signal handler or
           async I/O handler); see Py_AddPendingCall() and
           Py_MakePendingCalls() above. */

        if (--_Py_Ticker < 0) {
            if (*next_instr == SETUP_FINALLY) {
                /* Make the last opcode before
                   a try: finally: block uninterruptable. */
                goto fast_next_opcode;
            }
            _Py_Ticker = _Py_CheckInterval;
            tstate->tick_counter++;
#ifdef WITH_TSC
            ticked = 1;
#endif
            if (things_to_do) {
                if (Py_MakePendingCalls() < 0) {
                    why = WHY_EXCEPTION;
                    goto on_error;
                }
                if (things_to_do)
                    /* MakePendingCalls() didn't succeed.
                       Force early re-execution of this
                       "periodic" code, possibly after
                       a thread switch */
                    _Py_Ticker = 0;
            }
#ifdef WITH_THREAD
            if (interpreter_lock) {
                /* Give another thread a chance */

                if (PyThreadState_Swap(NULL) != tstate)
                    Py_FatalError("ceval: tstate mix-up");
                PyThread_release_lock(interpreter_lock);

                /* Other threads may run now */

                PyThread_acquire_lock(interpreter_lock, 1);
                if (PyThreadState_Swap(tstate) != NULL)
                    Py_FatalError("ceval: orphan tstate");

                /* Check for thread interrupts */

                if (tstate->async_exc != NULL) {
                    x = tstate->async_exc;
                    tstate->async_exc = NULL;
                    PyErr_SetNone(x);
                    Py_DECREF(x);
                    why = WHY_EXCEPTION;
                    goto on_error;
                }
            }
#endif
        }

    fast_next_opcode:
        f->f_lasti = INSTR_OFFSET();

        /* line-by-line tracing support */

        if (_Py_TracingPossible &&
            tstate->c_tracefunc != NULL && !tstate->tracing) {
            /* see maybe_call_line_trace
               for expository comments */
            f->f_stacktop = stack_pointer;

            err = maybe_call_line_trace(tstate->c_tracefunc,
                                        tstate->c_traceobj,
                                        f, &instr_lb, &instr_ub,
                                        &instr_prev);
            /* Reload possibly changed frame fields */
            JUMPTO(f->f_lasti);
            if (f->f_stacktop != NULL) {
                stack_pointer = f->f_stacktop;
                f->f_stacktop = NULL;
            }
            if (err) {
                /* trace function raised an exception */
                goto on_error;
            }
        }

        /* Extract opcode and argument */

        opcode = NEXTOP();
        oparg = 0;   /* allows oparg to be stored in a register because
            it doesn't have to be remembered across a full loop */
        if (HAS_ARG(opcode))
            oparg = NEXTARG();
    dispatch_opcode:
#ifdef DYNAMIC_EXECUTION_PROFILE
#ifdef DXPAIRS
        dxpairs[lastopcode][opcode]++;
        lastopcode = opcode;
#endif
        dxp[opcode]++;
#endif

#ifdef LLTRACE
        /* Instruction tracing */

        if (lltrace) {
            if (HAS_ARG(opcode)) {
                printf("%d: %d, %d\n",
                       f->f_lasti, opcode, oparg);
            }
            else {
                printf("%d: %d\n",
                       f->f_lasti, opcode);
            }
        }
#endif

        /* Main switch on opcode */
        READ_TIMESTAMP(inst0);

        switch (opcode) {

        /* BEWARE!
           It is essential that any operation that fails sets either
           x to NULL, err to nonzero, or why to anything but WHY_NOT,
           and that no operation that succeeds does this! */

        /* case STOP_CODE: this is an error! */

        case NOP:
            goto fast_next_opcode;

        case LOAD_FAST:
            x = GETLOCAL(oparg);
            if (x != NULL) {
                Py_INCREF(x);
                PUSH(x);
                goto fast_next_opcode;
            }
            format_exc_check_arg(PyExc_UnboundLocalError,
                UNBOUNDLOCAL_ERROR_MSG,
                PyTuple_GetItem(co->co_varnames, oparg));
            break;

        case LOAD_CONST:
            x = GETITEM(consts, oparg);
            Py_INCREF(x);
            PUSH(x);
            goto fast_next_opcode;