diff --git a/README.rst b/README.rst
index 8745af5..8988150 100644
--- a/README.rst
+++ b/README.rst
@@ -30,3 +30,9 @@ You can statically link any LGPL 3.0 code to code of permissive licenses
 (like MIT), and even to source-available license (like the SSPL or the
 Commons Clause) as long as the end user can recompile the program to use
 their own version of the library.
+
+----
+Todo
+----
+
+call before gc and after gc
diff --git a/c89_relo.c b/c89_relo.c
index f215c8f..6150781 100644
--- a/c89_relo.c
+++ b/c89_relo.c
@@ -56,13 +56,13 @@ static void check_len(void *rec, size_t i)
 	assert(i * sizeof(void *) < uns_c89_relo_get_len(rec));
 }
 
-void uns_c89_relo_record_set(void *rec, size_t i, void *v)
+void uns_c89_relo_record_set(Uns_ptr rec, size_t i, void *v)
 {
 	check_len(rec, i);
 	memcpy((unsigned char *)rec + i*sizeof(void*), &v, sizeof(v));
 }
 
-void *uns_c89_relo_record_get(void *rec, size_t i)
+void *uns_c89_relo_record_get(Uns_ptr rec, size_t i)
 {
 	void *v;
 
diff --git a/cheney_c89.c b/cheney_c89.c
index 25b248f..abdbb76 100644
--- a/cheney_c89.c
+++ b/cheney_c89.c
@@ -14,6 +14,7 @@
  * License along with this program. If not, see
  * <https://www.gnu.org/licenses/>.
 */
+#include <stdio.h>
 
 #include <stdlib.h>
 #include <limits.h>
@@ -53,6 +54,11 @@ static void *raw_alloc(struct ctx *ctx, size_t len, int is_record)
 {
 	unsigned char *p;
 
+/*
+	printf("%lu (%ld)\n", (unsigned long)(len + sizeof(struct uns_c89_relo_hdr)),
+                              (long)(ctx->tospace_end - ctx->tospace_alloc));
+*/
+	assert(ctx->tospace_alloc + sizeof(struct uns_c89_relo_hdr) + len <= ctx->tospace_end);
 	p = uns_c89_relo_init(ctx->tospace_alloc, len, is_record);
 	ctx->tospace_alloc = p + len;
 
@@ -89,8 +95,8 @@ static void scan_record(struct uns_gc *gc, unsigned char *p)
 	void *newp;
 
 	for (i = 0; i < l; i++) {
-		newp = relocate(gc, uns_c89_relo_record_get(p, i));
-		uns_c89_relo_record_set(p, i, newp);
+		newp = relocate(gc, uns_c89_relo_record_get((void *)p, i));
+		uns_c89_relo_record_set((void *)p, i, newp);
 	}
 }
 
@@ -118,6 +124,9 @@ int uns_cheney_c89_collect(struct uns_gc *gc)
 
 	/* Setup statistics */
 	gc->before_collection = fromspace_lim - fromspace;
+/*
+	printf("before: %ld\n", gc->before_collection);
+*/
 	gc->after_collection = 0;
 	gc->collection_number += 1;
 
@@ -170,7 +179,7 @@ void *uns_cheney_c89_alloc_record(struct uns_gc *gc, size_t records)
 	unsigned char *res = alloc(gc, records*sizeof(void *), 1);
 
 	for (i = 0; i < records; i++)
-		uns_c89_relo_record_set(res, i, NULL);
+		uns_c89_relo_record_set((void *)res, i, NULL);
 
 	return res;
 }
diff --git a/examples/string/Makefile b/examples/string/Makefile
index bf70827..6ec8882 100644
--- a/examples/string/Makefile
+++ b/examples/string/Makefile
@@ -4,6 +4,9 @@ COMMON_OBJS=../test_common.o uns_string.o
 .SUFFIXES: .test
 CFLAGS=-Wall -Wno-overlength-strings -std=c89 -Werror -pedantic -fPIC -g -Iinclude
 
+libunsstring.so: uns_string.o
+	$(CC) -shared -I../../include $(CFLAGS) $< -o libunsstring.so
+
 test: $(TESTS) $(COMMON_OBJS)
 	for i in $(TESTS); do \
 		LD_LIBRARY_PATH=$$(pwd)/../../ valgrind ./$$i || exit 1; \
diff --git a/include/internal/c89_relo.h b/include/internal/c89_relo.h
index 5347aa8..1226ce2 100644
--- a/include/internal/c89_relo.h
+++ b/include/internal/c89_relo.h
@@ -46,7 +46,7 @@ size_t uns_c89_relo_get_record_len(void *p);
 
 void *uns_c89_relo_init(void *p, size_t len_size, int is_record);
 
-void uns_c89_relo_record_set(void *rec, size_t i, void *v);
-void *uns_c89_relo_record_get(void *rec, size_t i);
+void uns_c89_relo_record_set(Uns_ptr rec, size_t i, void *v);
+void *uns_c89_relo_record_get(Uns_ptr rec, size_t i);
 
 #endif
diff --git a/uns.c b/uns.c
index 6ae6894..556a6aa 100644
--- a/uns.c
+++ b/uns.c
@@ -15,12 +15,16 @@
  * <https://www.gnu.org/licenses/>.
 */
 
+#include <assert.h>
 #include "uns.h"
 
 void uns_root_add(struct uns_gc *gc, struct uns_ctr *root)
 {
 	root->prev = NULL;
 	root->next = gc->roots;
+
+	if (gc->roots)
+		gc->roots->prev = root;
 	gc->roots = root;
 }
 
@@ -33,7 +37,10 @@ void uns_root_remove(struct uns_gc *gc, struct uns_ctr *root)
 		root->next->prev = root->prev;
 	}
 
-	if (gc->roots == root)
+	if (gc->roots == root) {
+		assert(!root->prev);
 		gc->roots = root->next;
+	}
+
 	root->prev = root->next = NULL;
 }