py/bc: Fix size calculation of UNWIND_JUMP opcode in mp_opcode_format.

Prior to this patch mp_opcode_format would calculate the incorrect size of
the MP_BC_UNWIND_JUMP opcode, missing the additional byte.  But, because
opcodes below 0x10 are unused and treated as bytes in the .mpy load/save
and freezing code, this bug did not show any symptoms, since nested unwind
jumps would rarely (if ever) reach a depth of 16 (so the extra byte of this
opcode would be between 0x01 and 0x0f and be correctly loaded/saved/frozen
simply as an undefined opcode).

This patch fixes this bug by correctly accounting for the additional byte.
        .

py/bc.c

@@ -292,7 +292,8 @@ continue2:;
 #if MICROPY_PERSISTENT_CODE_LOAD || MICROPY_PERSISTENT_CODE_SAVE
 
 // The following table encodes the number of bytes that a specific opcode
-// takes up.  There are 3 special opcodes that always have an extra byte:
+// takes up.  There are 4 special opcodes that always have an extra byte:
+//     MP_BC_UNWIND_JUMP
 //     MP_BC_MAKE_CLOSURE
 //     MP_BC_MAKE_CLOSURE_DEFARGS
 //     MP_BC_RAISE_VARARGS
@@ -402,7 +403,8 @@ uint mp_opcode_format(const byte *ip, size_t *opcode_size, bool count_var_uint)
         ip += 3;
     } else {
         int extra_byte = (
-            *ip == MP_BC_RAISE_VARARGS
+            *ip == MP_BC_UNWIND_JUMP
+            || *ip == MP_BC_RAISE_VARARGS
             || *ip == MP_BC_MAKE_CLOSURE
             || *ip == MP_BC_MAKE_CLOSURE_DEFARGS
         );

tests/basics/try_except_break.py

@@ -0,0 +1,73 @@
+# test deep unwind via break from nested try-except (22 of them)
+while True:
+ print(1)
+ try:
+  try:
+   try:
+    try:
+     try:
+      try:
+       try:
+        try:
+         try:
+          try:
+           try:
+            try:
+             try:
+              try:
+               try:
+                try:
+                 try:
+                  try:
+                   try:
+                    try:
+                     try:
+                      try:
+                       print(2)
+                       break
+                       print(3)
+                      except:
+                       pass
+                     except:
+                      pass
+                    except:
+                     pass
+                   except:
+                    pass
+                  except:
+                   pass
+                 except:
+                  pass
+                except:
+                 pass
+               except:
+                pass
+              except:
+               pass
+             except:
+              pass
+            except:
+             pass
+           except:
+            pass
+          except:
+           pass
+         except:
+          pass
+        except:
+         pass
+       except:
+        pass
+      except:
+       pass
+     except:
+      pass
+    except:
+     pass
+   except:
+    pass
+  except:
+   pass
+ except:
+  pass
+print(4)

tests/basics/try_except_break.py.exp

@@ -0,0 +1,3 @@
+1
+2
+4

tools/mpy-tool.py

@@ -109,6 +109,7 @@ def access(self, idx):
 MP_OPCODE_OFFSET = 3
 
 # extra bytes:
+MP_BC_UNWIND_JUMP = 0x46
 MP_BC_MAKE_CLOSURE = 0x62
 MP_BC_MAKE_CLOSURE_DEFARGS = 0x63
 MP_BC_RAISE_VARARGS = 0x5c
@@ -215,7 +216,8 @@ def mp_opcode_format(bytecode, ip, count_var_uint, opcode_format=make_opcode_for
         ip += 3
     else:
         extra_byte = (
-            opcode == MP_BC_RAISE_VARARGS
+            opcode == MP_BC_UNWIND_JUMP
+            or opcode == MP_BC_RAISE_VARARGS
             or opcode == MP_BC_MAKE_CLOSURE
             or opcode == MP_BC_MAKE_CLOSURE_DEFARGS
         )