It can be useful to have the processor registers writable when debugging a kernel, for example
for jtagfs. If they are not, the filesystem will protect you against it anyway.

Reference: /n/sources/patch/applied/rw-regs-map
Date: Mon Jul 11 11:45:55 CES 2011
Signed-off-by: paurea@gmail.com

--- /sys/src/libmach/map.c	Mon Jul 11 11:44:43 2011
+++ /sys/src/libmach/map.c	Mon Jul 11 11:44:41 2011
@@ -89,13 +89,11 @@
 	map = newmap(0, 4);
 	if (!map)
 		return 0;
-	if(kflag) {
+	if(kflag)
 		regs = "kregs";
-		mode = OREAD;
-	} else {
+	else
 		regs = "regs";
-		mode = ORDWR;
-	}
+	mode = ORDWR;
 	if (mach->regsize) {
 		sprint(buf, "/proc/%d/%s", pid, regs);
 		fd = open(buf, mode);