Index: sys/sys/kerneldump.h
===================================================================
--- sys/sys/kerneldump.h
+++ sys/sys/kerneldump.h
@@ -81,8 +81,8 @@
 #define	KERNELDUMPMAGIC_CLEARED	"Cleared Kernel Dump"
 	char		architecture[12];
 	uint32_t	version;
-#define	KERNELDUMPVERSION		3
-#define	KERNELDUMP_TEXT_VERSION		3
+#define	KERNELDUMPVERSION		4
+#define	KERNELDUMP_TEXT_VERSION		4
 	uint32_t	architectureversion;
 #define	KERNELDUMP_AARCH64_VERSION	1
 #define	KERNELDUMP_AMD64_VERSION	2
@@ -93,16 +93,19 @@
 #define	KERNELDUMP_RISCV_VERSION	1
 #define	KERNELDUMP_SPARC64_VERSION	1
 	uint64_t	dumplength;		/* excl headers */
-	uint64_t	dumpextent;
 	uint64_t	dumptime;
 	uint32_t	dumpkeysize;
 	uint32_t	blocksize;
-	uint8_t		compression;
 	char		hostname[64];
 	char		versionstring[192];
-	char		panicstring[179];
+	char		panicstring[175];
+	uint8_t		compression;
+	uint64_t	dumpextent;
+	char		unused[4];
 	uint32_t	parity;
 };
+_Static_assert(sizeof(struct kerneldumpheader) == 512,
+    "Expected block-sized kerneldumpheader");
 
 struct kerneldumpkey {
 	uint8_t		kdk_encryption;