Objects/codeobject.c

#include "Python.h"
#include "code.h"
#include "structmember.h"

#define NAME_CHARS \
    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz"

/* all_name_chars(s): true iff all chars in s are valid NAME_CHARS */

static int
all_name_chars(unsigned char *s)
{
    static char ok_name_char[256];
    static unsigned char *name_chars = (unsigned char *)NAME_CHARS;

    if (ok_name_char[*name_chars] == 0) {
        unsigned char *p;
        for (p = name_chars; *p; p++)
            ok_name_char[*p] = 1;
    }
    while (*s) {
        if (ok_name_char[*s++] == 0)
            return 0;
    }
    return 1;
}

static void
intern_strings(PyObject *tuple)
{
    Py_ssize_t i;

    for (i = PyTuple_GET_SIZE(tuple); --i >= 0; ) {
        PyObject *v = PyTuple_GET_ITEM(tuple, i);
        if (v == NULL || !PyString_CheckExact(v)) {
            Py_FatalError("non-string found in code slot");
        }
        PyString_InternInPlace(&PyTuple_GET_ITEM(tuple, i));
    }
}


PyCodeObject *
PyCode_New(int argcount, int nlocals, int stacksize, int flags,
           PyObject *code, PyObject *consts, PyObject *names,
           PyObject *varnames, PyObject *freevars, PyObject *cellvars,
           PyObject *filename, PyObject *name, int firstlineno,
           PyObject *lnotab)
{
    PyCodeObject *co;
    Py_ssize_t i;
    /* Check argument types */
    if (argcount < 0 || nlocals < 0 ||
        code == NULL ||
        consts == NULL || !PyTuple_Check(consts) ||
        names == NULL || !PyTuple_Check(names) ||
        varnames == NULL || !PyTuple_Check(varnames) ||
        freevars == NULL || !PyTuple_Check(freevars) ||
        cellvars == NULL || !PyTuple_Check(cellvars) ||
        name == NULL || !PyString_Check(name) ||
        filename == NULL || !PyString_Check(filename) ||
        lnotab == NULL || !PyString_Check(lnotab) ||
        !PyObject_CheckReadBuffer(code)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    intern_strings(names);
    intern_strings(varnames);
    intern_strings(freevars);
    intern_strings(cellvars);
    /* Intern selected string constants */
    for (i = PyTuple_Size(consts); --i >= 0; ) {
        PyObject *v = PyTuple_GetItem(consts, i);
        if (!PyString_Check(v))
            continue;
        if (!all_name_chars((unsigned char *)PyString_AS_STRING(v)))
            continue;
        PyString_InternInPlace(&PyTuple_GET_ITEM(consts, i));
    }
    co = PyObject_NEW(PyCodeObject, &PyCode_Type);
    if (co != NULL) {
        co->co_argcount = argcount;
        co->co_nlocals = nlocals;
        co->co_stacksize = stacksize;
        co->co_flags = flags;
        Py_INCREF(code);
        co->co_code = code;
        Py_INCREF(consts);
        co->co_consts = consts;
        Py_INCREF(names);
        co->co_names = names;
        Py_INCREF(varnames);
        co->co_varnames = varnames;
        Py_INCREF(freevars);
        co->co_freevars = freevars;
        Py_INCREF(cellvars);
        co->co_cellvars = cellvars;
        Py_INCREF(filename);
        co->co_filename = filename;
        Py_INCREF(name);
        co->co_name = name;
        co->co_firstlineno = firstlineno;
        Py_INCREF(lnotab);
        co->co_lnotab = lnotab;
        co->co_zombieframe = NULL;
    }
    return co;
}


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

static PyMemberDef code_memberlist[] = {
    {"co_argcount",     T_INT,          OFF(co_argcount),       READONLY},
    {"co_nlocals",      T_INT,          OFF(co_nlocals),        READONLY},
    {"co_stacksize",T_INT,              OFF(co_stacksize),      READONLY},
    {"co_flags",        T_INT,          OFF(co_flags),          READONLY},
    {"co_code",         T_OBJECT,       OFF(co_code),           READONLY},
    {"co_consts",       T_OBJECT,       OFF(co_consts),         READONLY},
    {"co_names",        T_OBJECT,       OFF(co_names),          READONLY},
    {"co_varnames",     T_OBJECT,       OFF(co_varnames),       READONLY},
    {"co_freevars",     T_OBJECT,       OFF(co_freevars),       READONLY},
    {"co_cellvars",     T_OBJECT,       OFF(co_cellvars),       READONLY},
    {"co_filename",     T_OBJECT,       OFF(co_filename),       READONLY},
    {"co_name",         T_OBJECT,       OFF(co_name),           READONLY},
    {"co_firstlineno", T_INT,           OFF(co_firstlineno),    READONLY},
    {"co_lnotab",       T_OBJECT,       OFF(co_lnotab),         READONLY},
    {NULL}      /* Sentinel */
};

/* Helper for code_new: return a shallow copy of a tuple that is
   guaranteed to contain exact strings, by converting string subclasses
   to exact strings and complaining if a non-string is found. */
static PyObject*
validate_and_copy_tuple(PyObject *tup)
{
    PyObject *newtuple;
    PyObject *item;
    Py_ssize_t i, len;

    len = PyTuple_GET_SIZE(tup);
    newtuple = PyTuple_New(len);
    if (newtuple == NULL)
        return NULL;

    for (i = 0; i < len; i++) {
        item = PyTuple_GET_ITEM(tup, i);
        if (PyString_CheckExact(item)) {
            Py_INCREF(item);
        }
        else if (!PyString_Check(item)) {
            PyErr_Format(
                PyExc_TypeError,
                "name tuples must contain only "
                "strings, not '%.500s'",
                item->ob_type->tp_name);
            Py_DECREF(newtuple);
            return NULL;
        }
        else {
            item = PyString_FromStringAndSize(
                PyString_AS_STRING(item),
                PyString_GET_SIZE(item));
            if (item == NULL) {
                Py_DECREF(newtuple);
                return NULL;
            }
        }
        PyTuple_SET_ITEM(newtuple, i, item);
    }

    return newtuple;
}

PyDoc_STRVAR(code_doc,
"code(argcount, nlocals, stacksize, flags, codestring, constants, names,\n\
      varnames, filename, name, firstlineno, lnotab[, freevars[, cellvars]])\n\
\n\
Create a code object.  Not for the faint of heart.");

static PyObject *
code_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
    int argcount;
    int nlocals;
    int stacksize;
    int flags;
    PyObject *co = NULL;
    PyObject *code;
    PyObject *consts;
    PyObject *names, *ournames = NULL;
    PyObject *varnames, *ourvarnames = NULL;
    PyObject *freevars = NULL, *ourfreevars = NULL;
    PyObject *cellvars = NULL, *ourcellvars = NULL;
    PyObject *filename;
    PyObject *name;
    int firstlineno;
    PyObject *lnotab;

    if (!PyArg_ParseTuple(args, "iiiiSO!O!O!SSiS|O!O!:code",
                          &argcount, &nlocals, &stacksize, &flags,
                          &code,
                          &PyTuple_Type, &consts,
                          &PyTuple_Type, &names,
                          &PyTuple_Type, &varnames,
                          &filename, &name,
                          &firstlineno, &lnotab,
                          &PyTuple_Type, &freevars,
                          &PyTuple_Type, &cellvars))
        return NULL;

    if (argcount < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: argcount must not be negative");
        goto cleanup;
    }

    if (nlocals < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: nlocals must not be negative");
        goto cleanup;
    }

    ournames = validate_and_copy_tuple(names);
    if (ournames == NULL)
        goto cleanup;
    ourvarnames = validate_and_copy_tuple(varnames);
    if (ourvarnames == NULL)
        goto cleanup;
    if (freevars)
        ourfreevars = validate_and_copy_tuple(freevars);
    else
        ourfreevars = PyTuple_New(0);
    if (ourfreevars == NULL)
        goto cleanup;
    if (cellvars)
        ourcellvars = validate_and_copy_tuple(cellvars);
    else
        ourcellvars = PyTuple_New(0);
    if (ourcellvars == NULL)
        goto cleanup;

    co = (PyObject *)PyCode_New(argcount, nlocals, stacksize, flags,
                                code, consts, ournames, ourvarnames,
                                ourfreevars, ourcellvars, filename,
                                name, firstlineno, lnotab);
  cleanup:
    Py_XDECREF(ournames);
    Py_XDECREF(ourvarnames);
    Py_XDECREF(ourfreevars);
    Py_XDECREF(ourcellvars);
    return co;
}

static void
code_dealloc(PyCodeObject *co)
{
    Py_XDECREF(co->co_code);
    Py_XDECREF(co->co_consts);
    Py_XDECREF(co->co_names);
    Py_XDECREF(co->co_varnames);
    Py_XDECREF(co->co_freevars);
    Py_XDECREF(co->co_cellvars);
    Py_XDECREF(co->co_filename);
    Py_XDECREF(co->co_name);
    Py_XDECREF(co->co_lnotab);
    if (co->co_zombieframe != NULL)
        PyObject_GC_Del(co->co_zombieframe);
    PyObject_DEL(co);
}

static PyObject *
code_repr(PyCodeObject *co)
{
    char buf[500];
    int lineno = -1;
    char *filename = "???";
    char *name = "???";

    if (co->co_firstlineno != 0)
        lineno = co->co_firstlineno;
    if (co->co_filename && PyString_Check(co->co_filename))
        filename = PyString_AS_STRING(co->co_filename);
    if (co->co_name && PyString_Check(co->co_name))
        name = PyString_AS_STRING(co->co_name);
    PyOS_snprintf(buf, sizeof(buf),
                  "<code object %.100s at %p, file \"%.300s\", line %d>",
                  name, co, filename, lineno);
    return PyString_FromString(buf);
}

static int
code_compare(PyCodeObject *co, PyCodeObject *cp)
{
    int cmp;
    cmp = PyObject_Compare(co->co_name, cp->co_name);
    if (cmp) return cmp;
    cmp = co->co_argcount - cp->co_argcount;
    if (cmp) goto normalize;
    cmp = co->co_nlocals - cp->co_nlocals;
    if (cmp) goto normalize;
    cmp = co->co_flags - cp->co_flags;
    if (cmp) goto normalize;
    cmp = co->co_firstlineno - cp->co_firstlineno;
    if (cmp) goto normalize;
    cmp = PyObject_Compare(co->co_code, cp->co_code);
    if (cmp) return cmp;
    cmp = PyObject_Compare(co->co_consts, cp->co_consts);
    if (cmp) return cmp;
    cmp = PyObject_Compare(co->co_names, cp->co_names);
    if (cmp) return cmp;
    cmp = PyObject_Compare(co->co_varnames, cp->co_varnames);
    if (cmp) return cmp;
    cmp = PyObject_Compare(co->co_freevars, cp->co_freevars);
    if (cmp) return cmp;
    cmp = PyObject_Compare(co->co_cellvars, cp->co_cellvars);
    return cmp;

 normalize:
    if (cmp > 0)
        return 1;
    else if (cmp < 0)
        return -1;
    else
        return 0;
}

static PyObject *
code_richcompare(PyObject *self, PyObject *other, int op)
{
    PyCodeObject *co, *cp;
    int eq;
    PyObject *res;

    if ((op != Py_EQ && op != Py_NE) ||
        !PyCode_Check(self) ||
        !PyCode_Check(other)) {

        /* Py3K warning if types are not equal and comparison
        isn't == or !=  */
        if (PyErr_WarnPy3k("code inequality comparisons not supported "
                           "in 3.x", 1) < 0) {
            return NULL;
        }

        Py_INCREF(Py_NotImplemented);
        return Py_NotImplemented;
    }

    co = (PyCodeObject *)self;
    cp = (PyCodeObject *)other;

    eq = PyObject_RichCompareBool(co->co_name, cp->co_name, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = co->co_argcount == cp->co_argcount;
    if (!eq) goto unequal;
    eq = co->co_nlocals == cp->co_nlocals;
    if (!eq) goto unequal;
    eq = co->co_flags == cp->co_flags;
    if (!eq) goto unequal;
    eq = co->co_firstlineno == cp->co_firstlineno;
    if (!eq) goto unequal;
    eq = PyObject_RichCompareBool(co->co_code, cp->co_code, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_consts, cp->co_consts, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_names, cp->co_names, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_varnames, cp->co_varnames, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_freevars, cp->co_freevars, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_cellvars, cp->co_cellvars, Py_EQ);
    if (eq <= 0) goto unequal;

    if (op == Py_EQ)
        res = Py_True;
    else
        res = Py_False;
    goto done;

  unequal:
    if (eq < 0)
        return NULL;
    if (op == Py_NE)
        res = Py_True;
    else
        res = Py_False;

  done:
    Py_INCREF(res);
    return res;
}

static long
code_hash(PyCodeObject *co)
{
    long h, h0, h1, h2, h3, h4, h5, h6;
    h0 = PyObject_Hash(co->co_name);
    if (h0 == -1) return -1;
    h1 = PyObject_Hash(co->co_code);
    if (h1 == -1) return -1;
    h2 = PyObject_Hash(co->co_consts);
    if (h2 == -1) return -1;
    h3 = PyObject_Hash(co->co_names);
    if (h3 == -1) return -1;
    h4 = PyObject_Hash(co->co_varnames);
    if (h4 == -1) return -1;
    h5 = PyObject_Hash(co->co_freevars);
    if (h5 == -1) return -1;
    h6 = PyObject_Hash(co->co_cellvars);
    if (h6 == -1) return -1;
    h = h0 ^ h1 ^ h2 ^ h3 ^ h4 ^ h5 ^ h6 ^
        co->co_argcount ^ co->co_nlocals ^ co->co_flags;
    if (h == -1) h = -2;
    return h;
}

/* XXX code objects need to participate in GC? */

PyTypeObject PyCode_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "code",
    sizeof(PyCodeObject),
    0,
    (destructor)code_dealloc,           /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    (cmpfunc)code_compare,              /* tp_compare */
    (reprfunc)code_repr,                /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    (hashfunc)code_hash,                /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT,                 /* tp_flags */
    code_doc,                           /* tp_doc */
    0,                                  /* tp_traverse */
    0,                                  /* tp_clear */
    code_richcompare,                                   /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    0,                                  /* tp_iter */
    0,                                  /* tp_iternext */
    0,                                  /* tp_methods */
    code_memberlist,                    /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    code_new,                           /* tp_new */
};

/* All about c_lnotab.

c_lnotab is an array of unsigned bytes disguised as a Python string.  In -O
mode, SET_LINENO opcodes aren't generated, and bytecode offsets are mapped
to source code line #s (when needed for tracebacks) via c_lnotab instead.
The array is conceptually a list of
    (bytecode offset increment, line number increment)
pairs.  The details are important and delicate, best illustrated by example:

    byte code offset    source code line number
    0                       1
    6                       2
       50                   7
      350                 307
      361                 308

The first trick is that these numbers aren't stored, only the increments
from one row to the next (this doesn't really work, but it's a start):

    0, 1,  6, 1,  44, 5,  300, 300,  11, 1

The second trick is that an unsigned byte can't hold negative values, or
values larger than 255, so (a) there's a deep assumption that byte code
offsets and their corresponding line #s both increase monotonically, and (b)
if at least one column jumps by more than 255 from one row to the next, more
than one pair is written to the table. In case #b, there's no way to know
from looking at the table later how many were written.  That's the delicate
part.  A user of c_lnotab desiring to find the source line number
corresponding to a bytecode address A should do something like this

    lineno = addr = 0
    for addr_incr, line_incr in c_lnotab:
    addr += addr_incr
    if addr > A:
        return lineno
    lineno += line_incr

In order for this to work, when the addr field increments by more than 255,
the line # increment in each pair generated must be 0 until the remaining addr
increment is < 256.  So, in the example above, com_set_lineno should not (as
was actually done until 2.2) expand 300, 300 to 255, 255,  45, 45, but to
255, 0,  45, 255,  0, 45.
*/

int
PyCode_Addr2Line(PyCodeObject *co, int addrq)
{
    int size = PyString_Size(co->co_lnotab) / 2;
    unsigned char *p = (unsigned char*)PyString_AsString(co->co_lnotab);
    int line = co->co_firstlineno;
    int addr = 0;
    while (--size >= 0) {
        addr += *p++;
        if (addr > addrq)
            break;
        line += *p++;
    }
    return line;
}

/*
   Check whether the current instruction is at the start of a line.

 */

    /* The theory of SET_LINENO-less tracing.

       In a nutshell, we use the co_lnotab field of the code object
       to tell when execution has moved onto a different line.

       As mentioned above, the basic idea is so set things up so
       that

         *instr_lb <= frame->f_lasti < *instr_ub

       is true so long as execution does not change lines.

       This is all fairly simple.  Digging the information out of
       co_lnotab takes some work, but is conceptually clear.

       Somewhat harder to explain is why we don't *always* call the
       line trace function when the above test fails.

       Consider this code:

       1: def f(a):
       2:     if a:
       3:        print 1
       4:     else:
       5:        print 2

       which compiles to this:

       2           0 LOAD_FAST                0 (a)
                   3 JUMP_IF_FALSE            9 (to 15)
                   6 POP_TOP

       3           7 LOAD_CONST               1 (1)
                  10 PRINT_ITEM
                  11 PRINT_NEWLINE
                  12 JUMP_FORWARD             6 (to 21)
         >>   15 POP_TOP

       5          16 LOAD_CONST               2 (2)
                  19 PRINT_ITEM
                  20 PRINT_NEWLINE
         >>   21 LOAD_CONST               0 (None)
              24 RETURN_VALUE

       If 'a' is false, execution will jump to instruction at offset
       15 and the co_lnotab will claim that execution has moved to
       line 3.  This is at best misleading.  In this case we could
       associate the POP_TOP with line 4, but that doesn't make
       sense in all cases (I think).

       What we do is only call the line trace function if the co_lnotab
       indicates we have jumped to the *start* of a line, i.e. if the
       current instruction offset matches the offset given for the
       start of a line by the co_lnotab.

       This also takes care of the situation where 'a' is true.
       Execution will jump from instruction offset 12 to offset 21.
       Then the co_lnotab would imply that execution has moved to line
       5, which is again misleading.

       Why do we set f_lineno when tracing?  Well, consider the code
       above when 'a' is true.  If stepping through this with 'n' in
       pdb, you would stop at line 1 with a "call" type event, then
       line events on lines 2 and 3, then a "return" type event -- but
       you would be shown line 5 during this event.  This is a change
       from the behaviour in 2.2 and before, and I've found it
       confusing in practice.  By setting and using f_lineno when
       tracing, one can report a line number different from that
       suggested by f_lasti on this one occasion where it's desirable.
    */


int
PyCode_CheckLineNumber(PyCodeObject* co, int lasti, PyAddrPair *bounds)
{
    int size, addr, line;
    unsigned char* p;

    p = (unsigned char*)PyString_AS_STRING(co->co_lnotab);
    size = PyString_GET_SIZE(co->co_lnotab) / 2;

    addr = 0;
    line = co->co_firstlineno;
    assert(line > 0);

    /* possible optimization: if f->f_lasti == instr_ub
       (likely to be a common case) then we already know
       instr_lb -- if we stored the matching value of p
       somwhere we could skip the first while loop. */

    /* see comments in compile.c for the description of
       co_lnotab.  A point to remember: increments to p
       should come in pairs -- although we don't care about
       the line increments here, treating them as byte
       increments gets confusing, to say the least. */

    bounds->ap_lower = 0;
    while (size > 0) {
        if (addr + *p > lasti)
            break;
        addr += *p++;
        if (*p)
            bounds->ap_lower = addr;
        line += *p++;
        --size;
    }

    /* If lasti and addr don't match exactly, we don't want to
       change the lineno slot on the frame or execute a trace
       function.  Return -1 instead.
    */
    if (addr != lasti)
        line = -1;

    if (size > 0) {
        while (--size >= 0) {
            addr += *p++;
            if (*p++)
                break;
        }
        bounds->ap_upper = addr;
    }
    else {
        bounds->ap_upper = INT_MAX;
    }

    return line;
}