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compile.c

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    • Damien George's avatar
      e1fb03f3
      py: Fix VM crash with unwinding jump out of a finally block. · e1fb03f3
      Damien George authored 
      This patch fixes a bug in the VM when breaking within a try-finally.  The
bug has to do with executing a break within the finally block of a
try-finally statement.  For example:

    def f():
        for x in (1,):
            print('a', x)
            try:
                raise Exception
            finally:
                print(1)
                break
            print('b', x)
    f()

Currently in uPy the above code will print:

    a 1
    1
    1
    segmentation fault (core dumped)  micropython

Not only is there a seg fault, but the "1" in the finally block is printed
twice.  This is because when the VM executes a finally block it doesn't
really know if that block was executed due to a fall-through of the try (no
exception raised), or because an exception is active.  In particular, for
nested finallys the VM has no idea which of the nested ones have active
exceptions and which are just fall-throughs.  So when a break (or continue)
is executed it tries to unwind all of the finallys, when in fact only some
may be active.

It's questionable whether break (or return or continue) should be allowed
within a finally block, because they implicitly swallow any active
exception, but nevertheless it's allowed by CPython (although almost never
used in the standard library).  And uPy should at least not crash in such a
case.

The solution here relies on the fact that exception and finally handlers
always appear in the bytecode after the try body.

Note: there was a similar bug with a return in a finally block, but that
was previously fixed in b7352084
      e1fb03f3
      History
      py: Fix VM crash with unwinding jump out of a finally block.
      Damien George authored 
      This patch fixes a bug in the VM when breaking within a try-finally.  The
bug has to do with executing a break within the finally block of a
try-finally statement.  For example:

    def f():
        for x in (1,):
            print('a', x)
            try:
                raise Exception
            finally:
                print(1)
                break
            print('b', x)
    f()

Currently in uPy the above code will print:

    a 1
    1
    1
    segmentation fault (core dumped)  micropython

Not only is there a seg fault, but the "1" in the finally block is printed
twice.  This is because when the VM executes a finally block it doesn't
really know if that block was executed due to a fall-through of the try (no
exception raised), or because an exception is active.  In particular, for
nested finallys the VM has no idea which of the nested ones have active
exceptions and which are just fall-throughs.  So when a break (or continue)
is executed it tries to unwind all of the finallys, when in fact only some
may be active.

It's questionable whether break (or return or continue) should be allowed
within a finally block, because they implicitly swallow any active
exception, but nevertheless it's allowed by CPython (although almost never
used in the standard library).  And uPy should at least not crash in such a
case.

The solution here relies on the fact that exception and finally handlers
always appear in the bytecode after the try body.

Note: there was a similar bug with a return in a finally block, but that
was previously fixed in b7352084
    builtin.c 14.14 KiB 
    #include <stdio.h>
#include <assert.h>

#include "nlr.h"
#include "misc.h"
#include "mpconfig.h"
#include "qstr.h"
#include "obj.h"
#include "objstr.h"
#include "runtime0.h"
#include "runtime.h"
#include "builtin.h"

#if MICROPY_ENABLE_FLOAT
#include <math.h>
#endif

// args[0] is function from class body
// args[1] is class name
// args[2:] are base objects
STATIC mp_obj_t mp_builtin___build_class__(uint n_args, const mp_obj_t *args) {
    assert(2 <= n_args);

    // set the new classes __locals__ object
    mp_obj_dict_t *old_locals = mp_locals_get();
    mp_obj_t class_locals = mp_obj_new_dict(0);
    mp_locals_set(class_locals);

    // call the class code
    mp_obj_t cell = mp_call_function_0(args[0]);

    // restore old __locals__ object
    mp_locals_set(old_locals);

    // get the class type (meta object) from the base objects
    mp_obj_t meta;
    if (n_args == 2) {
        // no explicit bases, so use 'type'
        meta = (mp_obj_t)&mp_type_type;
    } else {
        // use type of first base object
        meta = mp_obj_get_type(args[2]);
    }

    // TODO do proper metaclass resolution for multiple base objects

    // create the new class using a call to the meta object
    mp_obj_t meta_args[3];
    meta_args[0] = args[1]; // class name
    meta_args[1] = mp_obj_new_tuple(n_args - 2, args + 2); // tuple of bases
    meta_args[2] = class_locals; // dict of members
    mp_obj_t new_class = mp_call_function_n_kw(meta, 3, 0, meta_args);

    // store into cell if neede
    if (cell != mp_const_none) {
        mp_obj_cell_set(cell, new_class);
    }

    return new_class;
}

MP_DEFINE_CONST_FUN_OBJ_VAR(mp_builtin___build_class___obj, 2, mp_builtin___build_class__);

STATIC mp_obj_t mp_builtin___repl_print__(mp_obj_t o) {
    if (o != mp_const_none) {
        mp_obj_print(o, PRINT_REPR);
        printf("\n");
    }
    return mp_const_none;
}
    
MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin___repl_print___obj, mp_builtin___repl_print__);

mp_obj_t mp_builtin_abs(mp_obj_t o_in) {
    if (MP_OBJ_IS_SMALL_INT(o_in)) {
        mp_small_int_t val = MP_OBJ_SMALL_INT_VALUE(o_in);
        if (val < 0) {
            val = -val;
        }
        return MP_OBJ_NEW_SMALL_INT(val);
#if MICROPY_ENABLE_FLOAT
    } else if (MP_OBJ_IS_TYPE(o_in, &mp_type_float)) {
        mp_float_t value = mp_obj_float_get(o_in);
        // TODO check for NaN etc
        if (value < 0) {
            return mp_obj_new_float(-value);
        } else {
            return o_in;
        }
    } else if (MP_OBJ_IS_TYPE(o_in, &mp_type_complex)) {
        mp_float_t real, imag;
        mp_obj_complex_get(o_in, &real, &imag);
        return mp_obj_new_float(MICROPY_FLOAT_C_FUN(sqrt)(real*real + imag*imag));
#endif
    } else {
        assert(0);
        return mp_const_none;
    }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_abs_obj, mp_builtin_abs);

STATIC mp_obj_t mp_builtin_all(mp_obj_t o_in) {
    mp_obj_t iterable = mp_getiter(o_in);
    mp_obj_t item;
    while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
        if (!mp_obj_is_true(item)) {
            return mp_const_false;
        }
    }
    return mp_const_true;
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_all_obj, mp_builtin_all);

STATIC mp_obj_t mp_builtin_any(mp_obj_t o_in) {
    mp_obj_t iterable = mp_getiter(o_in);
    mp_obj_t item;
    while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
        if (mp_obj_is_true(item)) {
            return mp_const_true;
        }
    }
    return mp_const_false;
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_any_obj, mp_builtin_any);

STATIC mp_obj_t mp_builtin_bin(mp_obj_t o_in) {
    mp_obj_t args[] = { MP_OBJ_NEW_QSTR(MP_QSTR__brace_open__colon__hash_b_brace_close_), o_in };
    return mp_obj_str_format(ARRAY_SIZE(args), args);
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_bin_obj, mp_builtin_bin);

STATIC mp_obj_t mp_builtin_callable(mp_obj_t o_in) {
    if (mp_obj_is_callable(o_in)) {
        return mp_const_true;
    } else {
        return mp_const_false;
        }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_callable_obj, mp_builtin_callable);

STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
    int ord = mp_obj_get_int(o_in);
    if (0 <= ord && ord <= 0x10ffff) {
        byte str[1] = {ord};
        return mp_obj_new_str(str, 1, true);
    } else {
        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "chr() arg not in range(0x110000)"));
    }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_chr_obj, mp_builtin_chr);

STATIC mp_obj_t mp_builtin_dir(uint n_args, const mp_obj_t *args) {
    // TODO make this function more general and less of a hack

    mp_obj_dict_t *dict = NULL;
    if (n_args == 0) {
        // make a list of names in the local name space
        dict = mp_locals_get();
    } else { // n_args == 1
        // make a list of names in the given object
        if (MP_OBJ_IS_TYPE(args[0], &mp_type_module)) {
            dict = mp_obj_module_get_globals(args[0]);
        } else {
            mp_obj_type_t *type;
            if (MP_OBJ_IS_TYPE(args[0], &mp_type_type)) {
                type = args[0];
            } else {
                type = mp_obj_get_type(args[0]);
            }
            if (type->locals_dict != MP_OBJ_NULL && MP_OBJ_IS_TYPE(type->locals_dict, &mp_type_dict)) {
                dict = type->locals_dict;
            }
        }
    }

    mp_obj_t dir = mp_obj_new_list(0, NULL);
    if (dict != NULL) {
        for (uint i = 0; i < dict->map.alloc; i++) {
            if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
                mp_obj_list_append(dir, dict->map.table[i].key);
            }
        }
    }

    return dir;
}

MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_dir_obj, 0, 1, mp_builtin_dir);

STATIC mp_obj_t mp_builtin_divmod(mp_obj_t o1_in, mp_obj_t o2_in) {
    if (MP_OBJ_IS_SMALL_INT(o1_in) && MP_OBJ_IS_SMALL_INT(o2_in)) {
        mp_small_int_t i1 = MP_OBJ_SMALL_INT_VALUE(o1_in);
        mp_small_int_t i2 = MP_OBJ_SMALL_INT_VALUE(o2_in);
        mp_obj_t args[2];
        args[0] = MP_OBJ_NEW_SMALL_INT(i1 / i2);
        args[1] = MP_OBJ_NEW_SMALL_INT(i1 % i2);
        return mp_obj_new_tuple(2, args);
    } else {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "unsupported operand type(s) for divmod(): '%s' and '%s'", mp_obj_get_type_str(o1_in), mp_obj_get_type_str(o2_in)));
    }
}

MP_DEFINE_CONST_FUN_OBJ_2(mp_builtin_divmod_obj, mp_builtin_divmod);

    STATIC mp_obj_t mp_builtin_hash(mp_obj_t o_in) {
    // TODO hash will generally overflow small integer; can we safely truncate it?
    return mp_obj_new_int(mp_obj_hash(o_in));
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_hash_obj, mp_builtin_hash);

STATIC mp_obj_t mp_builtin_hex(mp_obj_t o_in) {
    return mp_binary_op(MP_BINARY_OP_MODULO, MP_OBJ_NEW_QSTR(MP_QSTR__percent__hash_x), o_in);
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_hex_obj, mp_builtin_hex);

STATIC mp_obj_t mp_builtin_iter(mp_obj_t o_in) {
    return mp_getiter(o_in);
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_iter_obj, mp_builtin_iter);

STATIC mp_obj_t mp_builtin_len(mp_obj_t o_in) {
    mp_obj_t len = mp_obj_len_maybe(o_in);
    if (len == NULL) {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "object of type '%s' has no len()", mp_obj_get_type_str(o_in)));
    } else {
        return len;
    }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_len_obj, mp_builtin_len);

STATIC mp_obj_t mp_builtin_max(uint n_args, const mp_obj_t *args) {
    if (n_args == 1) {
        // given an iterable
        mp_obj_t iterable = mp_getiter(args[0]);
        mp_obj_t max_obj = NULL;
        mp_obj_t item;
        while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
            if (max_obj == NULL || mp_binary_op(MP_BINARY_OP_LESS, max_obj, item)) {
                max_obj = item;
            }
        }
        if (max_obj == NULL) {
            nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "max() arg is an empty sequence"));
        }
        return max_obj;
    } else {
        // given many args
        mp_obj_t max_obj = args[0];
        for (int i = 1; i < n_args; i++) {
            if (mp_binary_op(MP_BINARY_OP_LESS, max_obj, args[i])) {
                max_obj = args[i];
            }
        }
        return max_obj;
    }
}

MP_DEFINE_CONST_FUN_OBJ_VAR(mp_builtin_max_obj, 1, mp_builtin_max);

STATIC mp_obj_t mp_builtin_min(uint n_args, const mp_obj_t *args) {
    if (n_args == 1) {
        // given an iterable
        mp_obj_t iterable = mp_getiter(args[0]);
        mp_obj_t min_obj = NULL;
        mp_obj_t item;
        while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
            if (min_obj == NULL || mp_binary_op(MP_BINARY_OP_LESS, item, min_obj)) {
                min_obj = item;
            }
        }
            if (min_obj == NULL) {
            nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "min() arg is an empty sequence"));
        }
        return min_obj;
    } else {
        // given many args
        mp_obj_t min_obj = args[0];
        for (int i = 1; i < n_args; i++) {
            if (mp_binary_op(MP_BINARY_OP_LESS, args[i], min_obj)) {
                min_obj = args[i];
            }
        }
        return min_obj;
    }
}

MP_DEFINE_CONST_FUN_OBJ_VAR(mp_builtin_min_obj, 1, mp_builtin_min);

STATIC mp_obj_t mp_builtin_next(mp_obj_t o) {
    mp_obj_t ret = mp_iternext_allow_raise(o);
    if (ret == MP_OBJ_STOP_ITERATION) {
        nlr_raise(mp_obj_new_exception(&mp_type_StopIteration));
    } else {
        return ret;
    }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_next_obj, mp_builtin_next);

STATIC mp_obj_t mp_builtin_oct(mp_obj_t o_in) {
    return mp_binary_op(MP_BINARY_OP_MODULO, MP_OBJ_NEW_QSTR(MP_QSTR__percent__hash_o), o_in);
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_oct_obj, mp_builtin_oct);

STATIC mp_obj_t mp_builtin_ord(mp_obj_t o_in) {
    uint len;
    const char *str = mp_obj_str_get_data(o_in, &len);
    if (len == 1) {
        // don't sign extend when converting to ord
        // TODO unicode
        return mp_obj_new_int(((const byte*)str)[0]);
    } else {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "ord() expected a character, but string of length %d found", len));
    }
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_ord_obj, mp_builtin_ord);

STATIC mp_obj_t mp_builtin_pow(uint n_args, const mp_obj_t *args) {
    assert(2 <= n_args && n_args <= 3);
    switch (n_args) {
        case 2: return mp_binary_op(MP_BINARY_OP_POWER, args[0], args[1]);
        default: return mp_binary_op(MP_BINARY_OP_MODULO, mp_binary_op(MP_BINARY_OP_POWER, args[0], args[1]), args[2]); // TODO optimise...
    }
}

MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_pow_obj, 2, 3, mp_builtin_pow);

STATIC mp_obj_t mp_builtin_print(uint n_args, const mp_obj_t *args, mp_map_t *kwargs) {
    mp_map_elem_t *sep_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_sep), MP_MAP_LOOKUP);
    mp_map_elem_t *end_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_end), MP_MAP_LOOKUP);
    const char *sep_data = " ";
    uint sep_len = 1;
    const char *end_data = "\n";
    uint end_len = 1;
    if (sep_elem != NULL && sep_elem->value != mp_const_none) {
        sep_data = mp_obj_str_get_data(sep_elem->value, &sep_len);
    }
    if (end_elem != NULL && end_elem->value != mp_const_none) {
            end_data = mp_obj_str_get_data(end_elem->value, &end_len);
    }
    for (int i = 0; i < n_args; i++) {
        if (i > 0) {
            printf("%.*s", sep_len, sep_data);
        }
        mp_obj_print(args[i], PRINT_STR);
    }
    printf("%.*s", end_len, end_data);
    return mp_const_none;
}

MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_print_obj, 0, mp_builtin_print);

STATIC mp_obj_t mp_builtin_repr(mp_obj_t o_in) {
    vstr_t *vstr = vstr_new();
    mp_obj_print_helper((void (*)(void *env, const char *fmt, ...))vstr_printf, vstr, o_in, PRINT_REPR);
    mp_obj_t s = mp_obj_new_str((byte*)vstr->buf, vstr->len, false);
    vstr_free(vstr);
    return s;
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);

STATIC mp_obj_t mp_builtin_sum(uint n_args, const mp_obj_t *args) {
    assert(1 <= n_args && n_args <= 2);
    mp_obj_t value;
    switch (n_args) {
        case 1: value = mp_obj_new_int(0); break;
        default: value = args[1]; break;
    }
    mp_obj_t iterable = mp_getiter(args[0]);
    mp_obj_t item;
    while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
        value = mp_binary_op(MP_BINARY_OP_ADD, value, item);
    }
    return value;
}

MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_sum_obj, 1, 2, mp_builtin_sum);

STATIC mp_obj_t mp_builtin_sorted(uint n_args, const mp_obj_t *args, mp_map_t *kwargs) {
    assert(n_args >= 1);
    if (n_args > 1) {
        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError,
                                          "must use keyword argument for key function"));
    }
    mp_obj_t self = mp_type_list.make_new((mp_obj_t)&mp_type_list, 1, 0, args);
    mp_obj_list_sort(1, &self, kwargs);

    return self;
}

MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj, 1, mp_builtin_sorted);

STATIC mp_obj_t mp_builtin_id(mp_obj_t o_in) {
    return mp_obj_new_int((machine_int_t)o_in);
}

MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_id_obj, mp_builtin_id);

// See mp_load_attr() if making any changes
STATIC inline mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t defval) {
    mp_obj_t dest[2];
    // use load_method, raising or not raising exception
    ((defval == MP_OBJ_NULL) ? mp_load_method : mp_load_method_maybe)(base, attr, dest);
    if (dest[0] == MP_OBJ_NULL) {
        return defval;
    } else if (dest[1] == MP_OBJ_NULL) {
        // load_method returned just a normal attribute
            return dest[0];
    } else {
        // load_method returned a method, so build a bound method object
        return mp_obj_new_bound_meth(dest[0], dest[1]);
    }
}

STATIC mp_obj_t mp_builtin_getattr(uint n_args, const mp_obj_t *args) {
    assert(MP_OBJ_IS_QSTR(args[1]));
    mp_obj_t defval = MP_OBJ_NULL;
    if (n_args > 2) {
        defval = args[2];
    }
    return mp_load_attr_default(args[0], MP_OBJ_QSTR_VALUE(args[1]), defval);
}

MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_getattr_obj, 2, 3, mp_builtin_getattr);

// These two are defined in terms of MicroPython API functions right away
MP_DEFINE_CONST_FUN_OBJ_0(mp_builtin_globals_obj, mp_globals_get);
MP_DEFINE_CONST_FUN_OBJ_0(mp_builtin_locals_obj, mp_locals_get);