py: Fix bug where GC collected native/viper/asm function data.

Because (for Thumb) a function pointer has the LSB set, pointers to
dynamic functions in RAM (eg native, viper or asm functions) were not
being traced by the GC.  This patch is a comprehensive fix for this.

Addresses issue #820.

4 files changed, 23 insertions, 0 deletions

diff --git a/tests/micropython/native.py b/tests/micropython/native.py
new file mode 100644
index 000000000..8f087c494
--- /dev/null
+++ b/tests/micropython/native.py
@@ -0,0 +1,10 @@
+@micropython.native
+def native_test(x):
+    print(1, [], x)
+
+native_test(2)
+
+# check that GC doesn't collect the native function
+import gc
+gc.collect()
+native_test(3)
diff --git a/tests/micropython/native.py.exp b/tests/micropython/native.py.exp
new file mode 100644
index 000000000..e1413fd79
--- /dev/null
+++ b/tests/micropython/native.py.exp
@@ -0,0 +1,2 @@
+1 [] 2
+1 [] 3
diff --git a/tests/micropython/viper.py b/tests/micropython/viper.py
index 5d4f4fd7b..7e6ed67d4 100644
--- a/tests/micropython/viper.py
+++ b/tests/micropython/viper.py
@@ -79,3 +79,12 @@ except SystemError as e:
 #@micropython.viper
 #def g() -> uint:
 #    return -1
+
+# calling GC after defining the function
+@micropython.viper
+def viper_gc() -> int:
+    return 1
+print(viper_gc())
+import gc
+gc.collect()
+print(viper_gc())
diff --git a/tests/micropython/viper.py.exp b/tests/micropython/viper.py.exp
index 28214aa17..2ea26ce99 100644
--- a/tests/micropython/viper.py.exp
+++ b/tests/micropython/viper.py.exp
@@ -9,3 +9,5 @@
 [1, 3]
 [1, 3]
 SystemError(1,)
+1
+1