[build] add a few pseudo targets to assist with building

list-arch and list-toolchain will compute and print the architecture and
toolchain needed to build the project the build is set to.

Used by the CI builder to decide what toolchain to grab.

engine.mk

@@ -1,7 +1,12 @@
 LOCAL_MAKEFILE:=$(MAKEFILE_LIST)
 
+# macros used all over the build system
+include make/macros.mk
+
 BUILDROOT ?= .
 
+# 'make spotless' is a special rule that skips most of the rest of the build system and
+# simply deletes everything in build-*
 ifeq ($(MAKECMDGOALS),spotless)
 spotless:
 	rm -rf -- "$(BUILDROOT)"/build-*
@@ -11,8 +16,8 @@ ifndef LKROOT
 $(error please define LKROOT to the root of the lk build system)
 endif
 
+# any local environment overrides can optionally be placed in local.mk
 -include local.mk
-include make/macros.mk
 
 # If one of our goals (from the commandline) happens to have a
 # matching project/goal.mk, then we should re-invoke make with
@@ -29,8 +34,8 @@ make-make:
 	@PROJECT=$(project-name) $(MAKE) -rR -f $(LOCAL_MAKEFILE) $(filter-out $(project-name), $(MAKECMDGOALS))
 
 .PHONY: make-make
-endif
-endif
+endif # expansion of project-name
+endif # project-name == null
 
 # some additional rules to print some help
 include make/help.mk
@@ -43,8 +48,9 @@ ifneq ($(DEFAULT_PROJECT),)
 PROJECT := $(DEFAULT_PROJECT)
 else
 $(error No project specified. Use 'make list' for a list of projects or 'make help' for additional help)
-endif
-endif
+endif # DEFAULT_PROJECT == something
+
+endif # PROJECT == null
 
 DEBUG ?= 2
 
@@ -271,12 +277,22 @@ clean: $(EXTRA_CLEANDEPS)
 install: all
 	scp $(OUTBIN) 192.168.0.4:/tftproot
 
+list-arch:
+	@echo ARCH = ${ARCH}
+
+list-toolchain:
+	@echo TOOLCHAIN_PREFIX = ${TOOLCHAIN_PREFIX}
+
+.PHONY: all clean install list-arch list-toolchain
+
 # generate a config.h file with all of the GLOBAL_DEFINES laid out in #define format
 configheader:
 
 $(CONFIGHEADER): configheader
 	@$(call MAKECONFIGHEADER,$@,GLOBAL_DEFINES)
 
+.PHONY: configheader
+
 # Empty rule for the .d files. The above rules will build .d files as a side
 # effect. Only works on gcc 3.x and above, however.
 %.d:
@@ -285,7 +301,6 @@ ifeq ($(filter $(MAKECMDGOALS), clean), )
 -include $(DEPS)
 endif
 
-.PHONY: configheader
-endif
+endif # do-nothing = 1
 
 endif # make spotless

make/help.mk

@@ -23,6 +23,9 @@ help:
 	@echo "make spotless: removes all build directories"
 	@echo "make <project>: try to build project named <project>"
 	@echo ""
+	@echo "make list-arch: print the architecture of the current project"
+	@echo "make list-toolchain: print the computed toolchain prefix of the current project"
+	@echo ""
 	@echo "Examples:"
 	@echo "PROJECT=testproject make"
 	@echo "PROJECT=testproject make clean"

make/macros.mk

@@ -1,3 +1,6 @@
+# A collection of handy macros used all over the build system.
+# This can be included anywhere and must not have any side effects.
+
 # Find the local dir of the make file
 GET_LOCAL_DIR    = $(patsubst %/,%,$(dir $(word $(words $(MAKEFILE_LIST)),$(MAKEFILE_LIST))))