diff --git a/include/lib/libfdt/libfdt.h b/include/lib/libfdt/libfdt.h
index 48f375c9c..544d3efff 100644
--- a/include/lib/libfdt/libfdt.h
+++ b/include/lib/libfdt/libfdt.h
@@ -9,6 +9,10 @@
 #include <libfdt_env.h>
 #include <fdt.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define FDT_FIRST_SUPPORTED_VERSION	0x02
 #define FDT_LAST_SUPPORTED_VERSION	0x11
 
@@ -2069,4 +2073,8 @@ int fdt_overlay_apply(void *fdt, void *fdto);
 
 const char *fdt_strerror(int errval);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* LIBFDT_H */
diff --git a/lib/libfdt/fdt.c b/lib/libfdt/fdt.c
index c28fcc115..6cf2fa03b 100644
--- a/lib/libfdt/fdt.c
+++ b/lib/libfdt/fdt.c
@@ -134,16 +134,20 @@ int fdt_check_header(const void *fdt)
 
 const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len)
 {
-	unsigned absoffset = offset + fdt_off_dt_struct(fdt);
+	unsigned int uoffset = offset;
+	unsigned int absoffset = offset + fdt_off_dt_struct(fdt);
+
+	if (offset < 0)
+		return NULL;
 
 	if (!can_assume(VALID_INPUT))
-		if ((absoffset < offset)
+		if ((absoffset < uoffset)
 		    || ((absoffset + len) < absoffset)
 		    || (absoffset + len) > fdt_totalsize(fdt))
 			return NULL;
 
 	if (can_assume(LATEST) || fdt_version(fdt) >= 0x11)
-		if (((offset + len) < offset)
+		if (((uoffset + len) < uoffset)
 		    || ((offset + len) > fdt_size_dt_struct(fdt)))
 			return NULL;
 
@@ -206,10 +210,11 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
 
 int fdt_check_node_offset_(const void *fdt, int offset)
 {
-	if (can_assume(VALID_INPUT))
-		return offset;
-	if ((offset < 0) || (offset % FDT_TAGSIZE)
-	    || (fdt_next_tag(fdt, offset, &offset) != FDT_BEGIN_NODE))
+	if (!can_assume(VALID_INPUT)
+	    && ((offset < 0) || (offset % FDT_TAGSIZE)))
+		return -FDT_ERR_BADOFFSET;
+
+	if (fdt_next_tag(fdt, offset, &offset) != FDT_BEGIN_NODE)
 		return -FDT_ERR_BADOFFSET;
 
 	return offset;
@@ -217,8 +222,11 @@ int fdt_check_node_offset_(const void *fdt, int offset)
 
 int fdt_check_prop_offset_(const void *fdt, int offset)
 {
-	if ((offset < 0) || (offset % FDT_TAGSIZE)
-	    || (fdt_next_tag(fdt, offset, &offset) != FDT_PROP))
+	if (!can_assume(VALID_INPUT)
+	    && ((offset < 0) || (offset % FDT_TAGSIZE)))
+		return -FDT_ERR_BADOFFSET;
+
+	if (fdt_next_tag(fdt, offset, &offset) != FDT_PROP)
 		return -FDT_ERR_BADOFFSET;
 
 	return offset;
@@ -306,9 +314,12 @@ const char *fdt_find_string_(const char *strtab, int tabsize, const char *s)
 
 int fdt_move(const void *fdt, void *buf, int bufsize)
 {
+	if (!can_assume(VALID_INPUT) && bufsize < 0)
+		return -FDT_ERR_NOSPACE;
+
 	FDT_RO_PROBE(fdt);
 
-	if (fdt_totalsize(fdt) > bufsize)
+	if (fdt_totalsize(fdt) > (unsigned int)bufsize)
 		return -FDT_ERR_NOSPACE;
 
 	memmove(buf, fdt, fdt_totalsize(fdt));
diff --git a/lib/libfdt/fdt_overlay.c b/lib/libfdt/fdt_overlay.c
index b310e49a6..d217e79b6 100644
--- a/lib/libfdt/fdt_overlay.c
+++ b/lib/libfdt/fdt_overlay.c
@@ -241,6 +241,7 @@ static int overlay_update_local_node_references(void *fdto,
 
 		if (fixup_len % sizeof(uint32_t))
 			return -FDT_ERR_BADOVERLAY;
+		fixup_len /= sizeof(uint32_t);
 
 		tree_val = fdt_getprop(fdto, tree_node, name, &tree_len);
 		if (!tree_val) {
@@ -250,7 +251,7 @@ static int overlay_update_local_node_references(void *fdto,
 			return tree_len;
 		}
 
-		for (i = 0; i < (fixup_len / sizeof(uint32_t)); i++) {
+		for (i = 0; i < fixup_len; i++) {
 			fdt32_t adj_val;
 			uint32_t poffset;
 
diff --git a/lib/libfdt/fdt_ro.c b/lib/libfdt/fdt_ro.c
index e03570a56..91cc6fefe 100644
--- a/lib/libfdt/fdt_ro.c
+++ b/lib/libfdt/fdt_ro.c
@@ -53,7 +53,7 @@ const char *fdt_get_string(const void *fdt, int stroffset, int *lenp)
 
 	err = -FDT_ERR_BADOFFSET;
 	absoffset = stroffset + fdt_off_dt_strings(fdt);
-	if (absoffset >= totalsize)
+	if (absoffset >= (unsigned)totalsize)
 		goto fail;
 	len = totalsize - absoffset;
 
@@ -61,17 +61,19 @@ const char *fdt_get_string(const void *fdt, int stroffset, int *lenp)
 		if (stroffset < 0)
 			goto fail;
 		if (can_assume(LATEST) || fdt_version(fdt) >= 17) {
-			if (stroffset >= fdt_size_dt_strings(fdt))
+			if ((unsigned)stroffset >= fdt_size_dt_strings(fdt))
 				goto fail;
 			if ((fdt_size_dt_strings(fdt) - stroffset) < len)
 				len = fdt_size_dt_strings(fdt) - stroffset;
 		}
 	} else if (fdt_magic(fdt) == FDT_SW_MAGIC) {
-		if ((stroffset >= 0)
-		    || (stroffset < -fdt_size_dt_strings(fdt)))
+		unsigned int sw_stroffset = -stroffset;
+
+		if ((stroffset >= 0) ||
+		    (sw_stroffset > fdt_size_dt_strings(fdt)))
 			goto fail;
-		if ((-stroffset) < len)
-			len = -stroffset;
+		if (sw_stroffset < len)
+			len = sw_stroffset;
 	} else {
 		err = -FDT_ERR_INTERNAL;
 		goto fail;
@@ -157,8 +159,8 @@ int fdt_generate_phandle(const void *fdt, uint32_t *phandle)
 
 static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
 {
-	int offset = n * sizeof(struct fdt_reserve_entry);
-	int absoffset = fdt_off_mem_rsvmap(fdt) + offset;
+	unsigned int offset = n * sizeof(struct fdt_reserve_entry);
+	unsigned int absoffset = fdt_off_mem_rsvmap(fdt) + offset;
 
 	if (!can_assume(VALID_INPUT)) {
 		if (absoffset < fdt_off_mem_rsvmap(fdt))
@@ -680,7 +682,7 @@ int fdt_node_offset_by_phandle(const void *fdt, uint32_t phandle)
 {
 	int offset;
 
-	if ((phandle == 0) || (phandle == -1))
+	if ((phandle == 0) || (phandle == ~0U))
 		return -FDT_ERR_BADPHANDLE;
 
 	FDT_RO_PROBE(fdt);
diff --git a/lib/libfdt/fdt_rw.c b/lib/libfdt/fdt_rw.c
index 93e4a2b56..68887b969 100644
--- a/lib/libfdt/fdt_rw.c
+++ b/lib/libfdt/fdt_rw.c
@@ -59,7 +59,7 @@ static int fdt_splice_(void *fdt, void *splicepoint, int oldlen, int newlen)
 
 	if ((oldlen < 0) || (soff + oldlen < soff) || (soff + oldlen > dsize))
 		return -FDT_ERR_BADOFFSET;
-	if ((p < (char *)fdt) || (dsize + newlen < oldlen))
+	if ((p < (char *)fdt) || (dsize + newlen < (unsigned)oldlen))
 		return -FDT_ERR_BADOFFSET;
 	if (dsize - oldlen + newlen > fdt_totalsize(fdt))
 		return -FDT_ERR_NOSPACE;
diff --git a/lib/libfdt/fdt_strerror.c b/lib/libfdt/fdt_strerror.c
index 768db66ea..b4356931b 100644
--- a/lib/libfdt/fdt_strerror.c
+++ b/lib/libfdt/fdt_strerror.c
@@ -40,7 +40,7 @@ static struct fdt_errtabent fdt_errtable[] = {
 	FDT_ERRTABENT(FDT_ERR_NOPHANDLES),
 	FDT_ERRTABENT(FDT_ERR_BADFLAGS),
 };
-#define FDT_ERRTABSIZE	(sizeof(fdt_errtable) / sizeof(fdt_errtable[0]))
+#define FDT_ERRTABSIZE	((int)(sizeof(fdt_errtable) / sizeof(fdt_errtable[0])))
 
 const char *fdt_strerror(int errval)
 {
@@ -48,7 +48,7 @@ const char *fdt_strerror(int errval)
 		return "<valid offset/length>";
 	else if (errval == 0)
 		return "<no error>";
-	else if (errval > -FDT_ERRTABSIZE) {
+	else if (-errval < FDT_ERRTABSIZE) {
 		const char *s = fdt_errtable[-errval].str;
 
 		if (s)
diff --git a/lib/libfdt/fdt_sw.c b/lib/libfdt/fdt_sw.c
index 26759d5df..68b543c4d 100644
--- a/lib/libfdt/fdt_sw.c
+++ b/lib/libfdt/fdt_sw.c
@@ -32,7 +32,7 @@ static int fdt_sw_probe_(void *fdt)
 /* 'memrsv' state:	Initial state after fdt_create()
  *
  * Allowed functions:
- *	fdt_add_reservmap_entry()
+ *	fdt_add_reservemap_entry()
  *	fdt_finish_reservemap()		[moves to 'struct' state]
  */
 static int fdt_sw_probe_memrsv_(void *fdt)
@@ -93,8 +93,8 @@ static inline uint32_t sw_flags(void *fdt)
 
 static void *fdt_grab_space_(void *fdt, size_t len)
 {
-	int offset = fdt_size_dt_struct(fdt);
-	int spaceleft;
+	unsigned int offset = fdt_size_dt_struct(fdt);
+	unsigned int spaceleft;
 
 	spaceleft = fdt_totalsize(fdt) - fdt_off_dt_struct(fdt)
 		- fdt_size_dt_strings(fdt);
@@ -108,8 +108,8 @@ static void *fdt_grab_space_(void *fdt, size_t len)
 
 int fdt_create_with_flags(void *buf, int bufsize, uint32_t flags)
 {
-	const size_t hdrsize = FDT_ALIGN(sizeof(struct fdt_header),
-					 sizeof(struct fdt_reserve_entry));
+	const int hdrsize = FDT_ALIGN(sizeof(struct fdt_header),
+				      sizeof(struct fdt_reserve_entry));
 	void *fdt = buf;
 
 	if (bufsize < hdrsize)
@@ -152,6 +152,9 @@ int fdt_resize(void *fdt, void *buf, int bufsize)
 
 	FDT_SW_PROBE(fdt);
 
+	if (bufsize < 0)
+		return -FDT_ERR_NOSPACE;
+
 	headsize = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
 	tailsize = fdt_size_dt_strings(fdt);
 
@@ -159,7 +162,7 @@ int fdt_resize(void *fdt, void *buf, int bufsize)
 	    headsize + tailsize > fdt_totalsize(fdt))
 		return -FDT_ERR_INTERNAL;
 
-	if ((headsize + tailsize) > bufsize)
+	if ((headsize + tailsize) > (unsigned)bufsize)
 		return -FDT_ERR_NOSPACE;
 
 	oldtail = (char *)fdt + fdt_totalsize(fdt) - tailsize;
@@ -247,18 +250,18 @@ int fdt_end_node(void *fdt)
 static int fdt_add_string_(void *fdt, const char *s)
 {
 	char *strtab = (char *)fdt + fdt_totalsize(fdt);
-	int strtabsize = fdt_size_dt_strings(fdt);
-	int len = strlen(s) + 1;
-	int struct_top, offset;
+	unsigned int strtabsize = fdt_size_dt_strings(fdt);
+	unsigned int len = strlen(s) + 1;
+	unsigned int struct_top, offset;
 
-	offset = -strtabsize - len;
+	offset = strtabsize + len;
 	struct_top = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
-	if (fdt_totalsize(fdt) + offset < struct_top)
+	if (fdt_totalsize(fdt) - offset < struct_top)
 		return 0; /* no more room :( */
 
-	memcpy(strtab + offset, s, len);
+	memcpy(strtab - offset, s, len);
 	fdt_set_size_dt_strings(fdt, strtabsize + len);
-	return offset;
+	return -offset;
 }
 
 /* Must only be used to roll back in case of error */
diff --git a/lib/libfdt/fdt_wip.c b/lib/libfdt/fdt_wip.c
index f64139e0b..c2d7566a6 100644
--- a/lib/libfdt/fdt_wip.c
+++ b/lib/libfdt/fdt_wip.c
@@ -23,7 +23,7 @@ int fdt_setprop_inplace_namelen_partial(void *fdt, int nodeoffset,
 	if (!propval)
 		return proplen;
 
-	if (proplen < (len + idx))
+	if ((unsigned)proplen < (len + idx))
 		return -FDT_ERR_NOSPACE;
 
 	memcpy((char *)propval + idx, val, len);