py: Fix compiling and decoding of *args at large arg positions.

There were two issues with the existing code:

1. "1 << i" is computed as a 32-bit number so would overflow when
   executed on 64-bit machines (when mp_uint_t is 64-bit).  This meant that
   *args beyond 32 positions would not be handled correctly.

2. star_args must fit as a positive small int so that it is encoded
   correctly in the emitted code.  MP_SMALL_INT_BITS is too big because it
   overflows a small int by 1 bit.  MP_SMALL_INT_BITS - 1 does not work
   because it produces a signed small int which is then sign extended when
   extracted (even by mp_obj_get_int_truncated), and this sign extension
   means that any position arg after *args is also treated as a star-arg.
   So the maximum bit position is MP_SMALL_INT_BITS - 2.  This means that
   MP_OBJ_SMALL_INT_VALUE() can be used instead of
   mp_obj_get_int_truncated() to get the value of star_args.

These issues are fixed by this commit, and a test added.

Signed-off-by: Damien George <damien@micropython.org>
This commit is contained in:
Damien George 2022-04-01 00:00:58 +11:00
parent e3de723e2d
commit bd556b6996
4 changed files with 44 additions and 6 deletions

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@ -2408,9 +2408,9 @@ STATIC void compile_trailer_paren_helper(compiler_t *comp, mp_parse_node_t pn_ar
return; return;
} }
#if MICROPY_DYNAMIC_COMPILER #if MICROPY_DYNAMIC_COMPILER
if (i > mp_dynamic_compiler.small_int_bits) if (i >= (size_t)mp_dynamic_compiler.small_int_bits - 1)
#else #else
if (i > MP_SMALL_INT_BITS) if (i >= MP_SMALL_INT_BITS - 1)
#endif #endif
{ {
// If there are not enough bits in a small int to fit the flag, then we consider // If there are not enough bits in a small int to fit the flag, then we consider
@ -2419,7 +2419,7 @@ STATIC void compile_trailer_paren_helper(compiler_t *comp, mp_parse_node_t pn_ar
return; return;
} }
star_flags |= MP_EMIT_STAR_FLAG_SINGLE; star_flags |= MP_EMIT_STAR_FLAG_SINGLE;
star_args |= 1 << i; star_args |= (mp_uint_t)1 << i;
compile_node(comp, pns_arg->nodes[0]); compile_node(comp, pns_arg->nodes[0]);
n_positional++; n_positional++;
} else if (MP_PARSE_NODE_STRUCT_KIND(pns_arg) == PN_arglist_dbl_star) { } else if (MP_PARSE_NODE_STRUCT_KIND(pns_arg) == PN_arglist_dbl_star) {

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@ -702,7 +702,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
} }
size_t n_args = n_args_n_kw & 0xff; size_t n_args = n_args_n_kw & 0xff;
size_t n_kw = (n_args_n_kw >> 8) & 0xff; size_t n_kw = (n_args_n_kw >> 8) & 0xff;
mp_uint_t star_args = mp_obj_get_int_truncated(args[n_args + 2 * n_kw]); mp_uint_t star_args = MP_OBJ_SMALL_INT_VALUE(args[n_args + 2 * n_kw]);
DEBUG_OP_printf("call method var (fun=%p, self=%p, n_args=%u, n_kw=%u, args=%p, map=%u)\n", fun, self, n_args, n_kw, args, star_args); DEBUG_OP_printf("call method var (fun=%p, self=%p, n_args=%u, n_kw=%u, args=%p, map=%u)\n", fun, self, n_args, n_kw, args, star_args);
@ -720,7 +720,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
if (star_args != 0) { if (star_args != 0) {
for (size_t i = 0; i < n_args; i++) { for (size_t i = 0; i < n_args; i++) {
if (star_args & (1 << i)) { if ((star_args >> i) & 1) {
mp_obj_t len = mp_obj_len_maybe(args[i]); mp_obj_t len = mp_obj_len_maybe(args[i]);
if (len != MP_OBJ_NULL) { if (len != MP_OBJ_NULL) {
// -1 accounts for 1 of n_args occupied by this arg // -1 accounts for 1 of n_args occupied by this arg
@ -773,7 +773,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
for (size_t i = 0; i < n_args; i++) { for (size_t i = 0; i < n_args; i++) {
mp_obj_t arg = args[i]; mp_obj_t arg = args[i];
if (star_args & (1 << i)) { if ((star_args >> i) & 1) {
// star arg // star arg
if (mp_obj_is_type(arg, &mp_type_tuple) || mp_obj_is_type(arg, &mp_type_list)) { if (mp_obj_is_type(arg, &mp_type_tuple) || mp_obj_is_type(arg, &mp_type_list)) {
// optimise the case of a tuple and list // optimise the case of a tuple and list

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@ -0,0 +1,36 @@
# Test the limit of the number of arguments to a function call.
# This currently tests the case of *args after many positional args.
def f(*args):
return len(args)
def test(n):
pos_args = ",".join(str(i) for i in range(n))
s = "f({}, *(100, 101), 102, 103)".format(pos_args)
try:
return eval(s)
except SyntaxError:
return "SyntaxError"
# If the port has at least 32-bits then this test should pass.
print(test(29))
# This test should fail on all ports (overflows a small int).
print(test(70))
# Check that there is a correct transition to the limit of too many args before *args.
reached_limit = False
for i in range(30, 70):
result = test(i)
if reached_limit:
if result != "SyntaxError":
print("FAIL")
else:
if result == "SyntaxError":
reached_limit = True
else:
if result != i + 4:
print("FAIL")

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@ -0,0 +1,2 @@
33
SyntaxError