1 files changed, 69 insertions, 0 deletions
diff --git a/common/dtb_reloc.c b/common/dtb_reloc.c
new file mode 100644
index 0000000..c3e0fe5
--- /dev/null
+++ b/common/dtb_reloc.c
@@ -0,0 +1,69 @@
+/*
+ * dtb_reloc.c - grow the devicetree the way libfdt does, in a
+ * buffer with room to spare. firmware cannot edit a packed fdt
+ * in place, new properties shift everything behind them, so the
+ * blob is copied into scratch verbatim, the free space after
+ * totalsize is the room the insert code shifts into, then the
+ * walkers patch the copy and the kernel gets its address.
+ *
+ * The layout follows the devicetree specification: header,
+ * struct block, strings block, free space. The rebuild copies
+ * header, struct, strings, fixes the offsets in the new header,
+ * and leaves the gap between struct and strings as the room new
+ * properties will consume.
+ *
+ * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
+ */
+
+#include <string.h>
+#include <endian.h>
+#include <boot.h>
+#include <dtb_patch.h>
+
+#define FDT_BEGIN_NODE	1
+#define FDT_END_NODE	2
+#define FDT_PROP	3
+#define FDT_NOP		4
+#define FDT_END		9
+
+static uint32_t be32(const void *p)
+{
+	const uint8_t *b = p;
+
+	return ((uint32_t)b[0] << 24) | ((uint32_t)b[1] << 16) |
+	       ((uint32_t)b[2] << 8) | (uint32_t)b[3];
+}
+
+/*
+ * copy the blob into the scratch, grow bytes of headroom after
+ * the end. returns the new blob address or 0 on a short buffer.
+ */
+uintptr_t tb_dtb_relocate(uintptr_t dtb, void *scratch, size_t scratch_size,
+			  size_t grow)
+{
+	uint8_t *in = (uint8_t *)dtb;
+	uint8_t *out = scratch;
+	uint32_t totalsize;
+
+	if (be32(in) != 0xd00dfeed)
+		return 0;
+
+	totalsize = be32(in + 4);
+
+	if (scratch_size < (size_t)totalsize + grow)
+		return 0;
+
+	/*
+	 * verbatim copy, byte for byte. the grow room is the free
+	 * scratch after totalsize, the insert code shifts the
+	 * strings block into it. an interior gap between the
+	 * struct and strings blocks only invites the walkers to
+	 * count it as tree.
+	 */
+	for (uint32_t i = 0; i < totalsize; i++)
+		out[i] = in[i];
+
+	(void)grow;
+
+	return (uintptr_t)out;
+}