Index: sys/powerpc/aim/locore.S
===================================================================
--- sys/powerpc/aim/locore.S
+++ sys/powerpc/aim/locore.S
@@ -6,3 +6,10 @@
 #include <powerpc/aim/locore32.S>
 #endif
 
+/*
+ * XXX: This should be moved to a shared AIM/booke asm file, if one ever is
+ * created.
+ */
+ENTRY(get_spr)
+	mfspr	%r3, 0
+	blr
Index: sys/powerpc/booke/locore.S
===================================================================
--- sys/powerpc/booke/locore.S
+++ sys/powerpc/booke/locore.S
@@ -846,6 +846,14 @@
 
 	blr
 
+/*
+ * XXX: This should be moved to a shared AIM/booke asm file, if one ever is
+ * created.
+ */
+ENTRY(get_spr)
+	mfspr	%r3, 0
+	blr
+
 /************************************************************************/
 /* Data section								*/
 /************************************************************************/
Index: sys/powerpc/powerpc/machdep.c
===================================================================
--- sys/powerpc/powerpc/machdep.c
+++ sys/powerpc/powerpc/machdep.c
@@ -516,3 +516,31 @@
 	}
 }
 
+/*
+ * Simple ddb(4) command/hack to view any SPR on the running CPU.
+ * Uses a trivial asm function to perform the mfspr, and rewrites the mfspr
+ * instruction each time.
+ * XXX: Since it uses code modification, it won't work if the kernel code pages
+ * are marked RO.
+ */
+extern register_t get_spr(int);
+
+DB_SHOW_COMMAND(spr, db_show_spr)
+{
+	register_t spr;
+	volatile uint32_t *p;
+	int sprno, saved_sprno;
+
+	if (!have_addr)
+		return;
+
+	saved_sprno = sprno = (intptr_t) addr;
+	sprno = ((sprno & 0x3e0) >> 5) | ((sprno & 0x1f) << 5);
+	p = (uint32_t *)(void *)&get_spr;
+	*p = (*p & ~0x001ff800) | (sprno << 11);
+	__syncicache(get_spr, cacheline_size);
+	spr = get_spr(sprno);
+
+	db_printf("SPR %d(%x): %lx\n", saved_sprno, saved_sprno,
+	    (unsigned long)spr);
+}