all: Fix signed shifts and NULL access errors from -fsanitize=undefined.

Fixes the following (the line numbers match commit 0e87459e2bfd07):

../../extmod/crypto-algorithms/sha256.c:49:19: runtime error: left shif...
../../extmod/moduasyncio.c:106:35: runtime error: member access within ...
../../py/binary.c:210:13: runtime error: left shift of negative value -...
../../py/mpz.c:744:16: runtime error: negation of -9223372036854775808 ...
../../py/objint.c:109:22: runtime error: left shift of 1 by 31 places c...
../../py/objint_mpz.c:374:9: runtime error: left shift of 4611686018427...
../../py/objint_mpz.c:374:9: runtime error: left shift of negative valu...
../../py/parsenum.c:106:14: runtime error: left shift of 46116860184273...
../../py/runtime.c:395:33: runtime error: left shift of negative value ...
../../py/showbc.c:177:28: runtime error: left shift of negative value -...
../../py/vm.c:321:36: runtime error: left shift of negative value -1```

Testing was done on an amd64 Debian Buster system using gcc-8.3 and these
settings:

    CFLAGS += -g3 -Og -fsanitize=undefined
    LDFLAGS += -fsanitize=undefined

The introduced TASK_PAIRHEAP macro's conditional (x ? &x->i : NULL)
assembles (under amd64 gcc 8.3 -Os) to the same as &x->i, since i is the
initial field of the struct.  However, for the purposes of undefined
behavior analysis the conditional is needed.

Signed-off-by: Jeff Epler <jepler@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/py/vm.c b/py/vm.c
index f9a589c9d..5365014fc 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -312,7 +312,7 @@ dispatch_loop:
                     DISPATCH();
 
                 ENTRY(MP_BC_LOAD_CONST_SMALL_INT): {
-                    mp_int_t num = 0;
+                    mp_uint_t num = 0;
                     if ((ip[0] & 0x40) != 0) {
                         // Number is negative
                         num--;