Seems I forgot to add prof.html to the list of files to install.
(sigh)
--- mk/doc.mk~ 2015-08-05 04:18:46.000000000 +0000
+++ mk/doc.mk
@@ -3,7 +3,7 @@
#
HTML=devices.html gdb.html index.html install.html lamebus.html \
- mips.html networking.html system.html
+ mips.html networking.html prof.html system.html
include defs.mk