The flags are:
+f
+ Include the function name in the printed message
+l
+ Include line number in the printed message
+m
+ Include module name in the printed message
p
Causes a printk() message to be emitted to dmesg
+t
+ Include thread ID in messages not generated from interrupt context
-Note the regexp ^[-+=][scp]+$ matches a flags specification.
+Note the regexp ^[-+=][flmpt]+$ matches a flags specification.
Note also that there is no convenient syntax to remove all
-the flags at once, you need to use "-psc".
+the flags at once, you need to use "-flmpt".
Debug messages during boot process