In config/config.mk, there is a make function core_winabspath that fails with my directory layout. I have a directory /local-t that contains my source tree. It is actually at c:\mozilla-build\msys. When building a .fake lib file, it produces paths such as local-t:\js\src\... These are invalid. I resolved it by changing from core_winabspath = $(firstword $(subst /, ,$(call core_abspath,$(1)))):$(subst $(space),,$(patsubst %,\\%,$(wordlist 2,$(words $(subst /, ,$(call core_abspath,$(1)))), $(strip $(subst /, ,$(call core_abspath,$(1))))))) to core_winabspath = $(shell cd $(dir $(1)); pwd -W)/$(notdir $(1)) which is probably much slower but gives the correct answer. Perhaps something in between would be best -- use the pwd -W method to find and memoize the windows path to the obj dir, then textually substitute for the rest?

This build configuration is unsupported. You must build from /x/foo paths, not from within the MSYS root directory. We've talked about adding an $(error) to make this more obvious. khuey, did you have a plan for that?