diff --git a/py/emitnative.c b/py/emitnative.c
index 211d2895a3..c7cbbf4516 100644
--- a/py/emitnative.c
+++ b/py/emitnative.c
@@ -1174,6 +1174,7 @@ STATIC void emit_native_load_const_str(emit_t *emit, qstr qst, bool bytes) {
 
 STATIC void emit_native_load_const_obj(emit_t *emit, void *obj) {
     emit_native_pre(emit);
+    need_reg_single(emit, REG_RET, 0);
     ASM_MOV_ALIGNED_IMM_TO_REG(emit->as, (mp_uint_t)obj, REG_RET);
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 541f7c75a5..5718ffacbc 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -569,6 +569,9 @@ typedef double mp_float_t;
 #define MICROPY_MAKE_POINTER_CALLABLE(p) (p)
 #endif
 
+// If these MP_PLAT_* macros are overridden then the memory allocated by them
+// must be somehow reachable for marking by the GC, since the native code
+// generators store pointers to GC managed memory in the code.
 #ifndef MP_PLAT_ALLOC_EXEC
 #define MP_PLAT_ALLOC_EXEC(min_size, ptr, size) do { *ptr = m_new(byte, min_size); *size = min_size; } while(0)
 #endif
diff --git a/unix/alloc.c b/unix/alloc.c
index cb866c78a2..44a84437ec 100644
--- a/unix/alloc.c
+++ b/unix/alloc.c
@@ -24,16 +24,29 @@
  * THE SOFTWARE.
  */
 
+#include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/mman.h>
 
-#include "mpconfigport.h"
+#include "py/mpstate.h"
+#include "py/gc.h"
 
 #if defined(__OpenBSD__) || defined(__MACH__)
 #define MAP_ANONYMOUS MAP_ANON
 #endif
 
+// The memory allocated here is not on the GC heap (and it may contain pointers
+// that need to be GC'd) so we must somehow trace this memory.  We do it by
+// keeping a linked list of all mmap'd regions, and tracing them explicitly.
+
+typedef struct _mmap_region_t {
+    void *ptr;
+    size_t len;
+    struct _mmap_region_t *next;
+} mmap_region_t;
+
 void mp_unix_alloc_exec(mp_uint_t min_size, void **ptr, mp_uint_t *size) {
     // size needs to be a multiple of the page size
     *size = (min_size + 0xfff) & (~0xfff);
@@ -41,8 +54,31 @@ void mp_unix_alloc_exec(mp_uint_t min_size, void **ptr, mp_uint_t *size) {
     if (*ptr == MAP_FAILED) {
         *ptr = NULL;
     }
+
+    // add new link to the list of mmap'd regions
+    mmap_region_t *rg = m_new_obj(mmap_region_t);
+    rg->ptr = *ptr;
+    rg->len = min_size;
+    rg->next = MP_STATE_VM(mmap_region_head);
+    MP_STATE_VM(mmap_region_head) = rg;
 }
 
 void mp_unix_free_exec(void *ptr, mp_uint_t size) {
     munmap(ptr, size);
+
+    // unlink the mmap'd region from the list
+    for (mmap_region_t **rg = (mmap_region_t**)&MP_STATE_VM(mmap_region_head); *rg != NULL; *rg = (*rg)->next) {
+        if ((*rg)->ptr == ptr) {
+            mmap_region_t *next = (*rg)->next;
+            m_del_obj(mmap_region_t, *rg);
+            *rg = next;
+            return;
+        }
+    }
+}
+
+void mp_unix_mark_exec(void) {
+    for (mmap_region_t *rg = MP_STATE_VM(mmap_region_head); rg != NULL; rg = rg->next) {
+        gc_collect_root(rg->ptr, rg->len / sizeof(mp_uint_t));
+    }
 }
diff --git a/unix/gccollect.c b/unix/gccollect.c
index 16bfc3b486..52dac01bd2 100644
--- a/unix/gccollect.c
+++ b/unix/gccollect.c
@@ -31,8 +31,6 @@
 
 #if MICROPY_ENABLE_GC
 
-extern char *stack_top;
-
 #if MICROPY_GCREGS_SETJMP
 #include <setjmp.h>
 
@@ -133,6 +131,7 @@ void gc_collect(void) {
     // GC stack (and regs because we captured them)
     void **regs_ptr = (void**)(void*)&regs;
     gc_collect_root(regs_ptr, ((mp_uint_t)MP_STATE_VM(stack_top) - (mp_uint_t)&regs) / sizeof(mp_uint_t));
+    mp_unix_mark_exec();
     gc_collect_end();
 
     //printf("-----\n");
diff --git a/unix/mpconfigport.h b/unix/mpconfigport.h
index 3f5d577038..a1acb5f5c4 100644
--- a/unix/mpconfigport.h
+++ b/unix/mpconfigport.h
@@ -148,6 +148,7 @@ typedef const void *machine_const_ptr_t; // must be of pointer size
 
 void mp_unix_alloc_exec(mp_uint_t min_size, void** ptr, mp_uint_t *size);
 void mp_unix_free_exec(void *ptr, mp_uint_t size);
+void mp_unix_mark_exec(void);
 #define MP_PLAT_ALLOC_EXEC(min_size, ptr, size) mp_unix_alloc_exec(min_size, ptr, size)
 #define MP_PLAT_FREE_EXEC(ptr, size) mp_unix_free_exec(ptr, size)
 
@@ -158,7 +159,8 @@ extern const struct _mp_obj_fun_builtin_t mp_builtin_open_obj;
     { MP_OBJ_NEW_QSTR(MP_QSTR_open), (mp_obj_t)&mp_builtin_open_obj },
 
 #define MICROPY_PORT_ROOT_POINTERS \
-    mp_obj_t keyboard_interrupt_obj;
+    mp_obj_t keyboard_interrupt_obj; \
+    void *mmap_region_head; \
 
 // We need to provide a declaration/definition of alloca()
 #ifdef __FreeBSD__