diff --git a/src/emu/CMakeLists.txt b/src/emu/CMakeLists.txt
index ec7aff7..f081dd2 100644
--- a/src/emu/CMakeLists.txt
+++ b/src/emu/CMakeLists.txt
@@ -1,4 +1,4 @@
-# Copyright (c) 2021-2022 Barcelona Supercomputing Center (BSC)
+# Copyright (c) 2021-2023 Barcelona Supercomputing Center (BSC)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 include_directories(
@@ -42,6 +42,7 @@ add_library(emu STATIC
   track.c
   thread.c
   extend.c
+  value.c
   ovni/event.c
   ovni/setup.c
   nanos6/setup.c
diff --git a/src/emu/chan.c b/src/emu/chan.c
index b2a787e..fccfe7c 100644
--- a/src/emu/chan.c
+++ b/src/emu/chan.c
@@ -71,9 +71,8 @@ check_duplicates(struct chan *chan, struct value *v)
 		return 0;
 
 	if (value_is_equal(&chan->last_value, v)) {
-		char buf[128];
 		err("%s: same value as last_value %s",
-				chan->name, value_str(chan->last_value, buf));
+				chan->name, value_str(chan->last_value));
 		return -1;
 	}
 
@@ -98,10 +97,7 @@ chan_set(struct chan *chan, struct value value)
 		return -1;
 	}
 
-#ifdef ENABLE_DEBUG
-	char buf[128];
-	dbg("%s: sets value to %s", chan->name, value_str(value, buf));
-#endif
+	dbg("%s: sets value to %s", chan->name, value_str(value));
 	chan->data.value = value;
 
 	if (set_dirty(chan) != 0) {
diff --git a/src/emu/mux.c b/src/emu/mux.c
index 474978f..e6a374c 100644
--- a/src/emu/mux.c
+++ b/src/emu/mux.c
@@ -77,7 +77,7 @@ cb_select(struct chan *sel_chan, void *ptr)
 	char buf[128];
 	UNUSED(buf);
 	dbg("select channel got value %s\n",
-			value_str(sel_value, buf));
+			value_str(sel_value));
 
 	struct mux_input *input = NULL;
 	if (select_input(mux, sel_value, &input) != 0) {
@@ -90,7 +90,7 @@ cb_select(struct chan *sel_chan, void *ptr)
 		input->selected = 1;
 		mux->selected = input->index;
 		dbg("mux selects input key=%s chan=%s\n",
-				value_str(sel_value, buf), input->chan->name);
+				value_str(sel_value), input->chan->name);
 	}
 
 	/* Set to null by default */
@@ -123,9 +123,8 @@ cb_input(struct chan *in_chan, void *ptr)
 		return -1;
 	}
 
-	char buf[128];
 	dbg("setting output chan %s to value %s",
-			input->output->name, value_str(out_value, buf));
+			input->output->name, value_str(out_value));
 
 	if (chan_set(input->output, out_value) != 0) {
 		err("chan_set() failed");
diff --git a/src/emu/pv/prv.c b/src/emu/pv/prv.c
index a5e5ad7..c7fa205 100644
--- a/src/emu/pv/prv.c
+++ b/src/emu/pv/prv.c
@@ -88,7 +88,6 @@ emit(struct prv *prv, struct prv_chan *rchan)
 {
 	struct value value;
 	struct chan *chan = rchan->chan;
-	char buf[128];
 	if (chan_read(chan, &value) != 0) {
 		err("chan_read %s failed\n", chan->name);
 		return -1;
@@ -106,7 +105,7 @@ emit(struct prv *prv, struct prv_chan *rchan)
 				return 0;
 
 			err("error duplicated value %s for channel %s\n",
-					value_str(value, buf), chan->name);
+					value_str(value), chan->name);
 			return -1;
 		}
 
@@ -125,7 +124,7 @@ emit(struct prv *prv, struct prv_chan *rchan)
 			if (~rchan->flags & PRV_ZERO && val == 0) {
 				err("forbidden value 0 in %s: %s\n",
 						chan->name,
-						value_str(value, buf));
+						value_str(value));
 				return -1;
 			}
 			break;
@@ -134,13 +133,13 @@ emit(struct prv *prv, struct prv_chan *rchan)
 			break;
 		default:
 			err("chan_read %s only int64 and null supported: %s\n",
-					chan->name, value_str(value, buf));
+					chan->name, value_str(value));
 			return -1;
 	}
 
 	write_line(prv, rchan->row_base1, rchan->type, val);
 
-	dbg("written %s for chan %s", value_str(value, buf), chan->name);
+	dbg("written %s for chan %s", value_str(value), chan->name);
 
 
 	return 0;
diff --git a/src/emu/value.c b/src/emu/value.c
new file mode 100644
index 0000000..a382a7c
--- /dev/null
+++ b/src/emu/value.c
@@ -0,0 +1,7 @@
+/* Copyright (c) 2023 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include "value.h"
+
+char value_buffers[VALUE_NBUF][VALUE_BUFSIZE];
+size_t value_nextbuf = 0;
diff --git a/src/emu/value.h b/src/emu/value.h
index 330c4de..5ec8395 100644
--- a/src/emu/value.h
+++ b/src/emu/value.h
@@ -9,6 +9,12 @@
 #include <stdio.h>
 #include "common.h"
 
+#define VALUE_NBUF 32
+#define VALUE_BUFSIZE 128
+
+extern char value_buffers[VALUE_NBUF][VALUE_BUFSIZE];
+extern size_t value_nextbuf;
+
 enum value_type {
 	VALUE_NULL = 0,
 	VALUE_INT64,
@@ -51,22 +57,33 @@ value_is_null(struct value a)
 }
 
 static inline char *
-value_str(struct value a, char *buf)
+value_str(struct value a)
 {
+	char *buf = value_buffers[value_nextbuf];
+	int ret = 0;
+	size_t n = VALUE_BUFSIZE;
+
 	switch (a.type) {
 		case VALUE_NULL:
-			sprintf(buf, "{NULL}");
+			ret = snprintf(buf, n, "{NULL}");
 			break;
 		case VALUE_INT64:
-			sprintf(buf, "{int64_t %ld}", a.i);
+			ret = snprintf(buf, n, "{int64_t %ld}", a.i);
 			break;
 		case VALUE_DOUBLE:
-			sprintf(buf, "{double %e}", a.d);
+			ret = snprintf(buf, n, "{double %e}", a.d);
 			break;
 		default:
 			die("value_str: unexpected value type\n");
 	}
 
+	if (ret >= (int) n)
+		die("value string too long");
+
+	value_nextbuf++;
+	if (value_nextbuf > VALUE_NBUF)
+		value_nextbuf = 0;
+
 	return buf;
 }
 
diff --git a/test/unit/mux.c b/test/unit/mux.c
index 5891535..46f7ff9 100644
--- a/test/unit/mux.c
+++ b/test/unit/mux.c
@@ -14,11 +14,9 @@ check_output(struct mux *mux, struct value expected)
 		die("chan_read() failed for output channel\n");
 
 	if (!value_is_equal(&out_value, &expected)) {
-		char buf1[128];
-		char buf2[128];
 		die("unexpected value found %s in output (expected %s)\n",
-				value_str(out_value, buf1),
-				value_str(expected, buf2));
+				value_str(out_value),
+				value_str(expected));
 	}
 
 	err("----- output ok -----\n");
diff --git a/test/unit/value.c b/test/unit/value.c
index c6738c7..bdff9f9 100644
--- a/test/unit/value.c
+++ b/test/unit/value.c
@@ -4,8 +4,9 @@
 #include "emu/value.h"
 #include "common.h"
 
-int
-main(void)
+/* Ensure there are no holes in the value structure */
+static void
+test_holes(void)
 {
 	struct value a, b;
 
@@ -21,6 +22,16 @@ main(void)
 		die("values are not the same\n");
 
 	err("OK\n");
+}
+
+/* Ensure value_null results in values being equal */
+static void
+test_null_init(void)
+{
+	struct value a, b;
+
+	memset(&a, 66, sizeof(struct value));
+	memset(&b, 0, sizeof(struct value));
 
 	a = value_null();
 	b = value_null();
@@ -28,5 +39,42 @@ main(void)
 	if (!value_is_equal(&a, &b))
 		die("null not equal");
 
+	err("OK\n");
+}
+
+/* Test that we can printf at least 8 values without overwritting the
+ * value_str() buffer */
+static void
+test_multiple_str(void)
+{
+	if (VALUE_NBUF < 8)
+		die("VALUE_NBUF too small");
+
+	char *str[VALUE_NBUF];
+	for (int i = 0; i < VALUE_NBUF; i++) {
+		struct value v = value_int64(i);
+		str[i] = value_str(v);
+	}
+
+	for (int i = 0; i < VALUE_NBUF; i++) {
+		char expected[128];
+		sprintf(expected, "{int64_t %d}", i);
+		if (strcmp(expected, str[i]) != 0) {
+			die("mismatch in bufer i=%d: expected %s, got %s",
+					i, expected, str[i]);
+		}
+	}
+
+	err("OK");
+}
+
+
+int
+main(void)
+{
+	test_holes();
+	test_null_init();
+	test_multiple_str();
+
 	return 0;
 }