Makefile.include: add rule to verify thin archives.

Thin archives should be created with relative paths so that archives created
in a build container are useful in the host. This check ensures there are no
absolute paths inside thin archives.
that there are

Makefile.base

@@ -67,12 +67,10 @@ $(BINDIR)/$(MODULE)/:
 
 $(BINDIR)/$(MODULE).a $(OBJ): | $(BINDIR)/$(MODULE)/
 
-relpath = $(shell realpath --relative-to=$(abspath .) $(1))
-
 $(BINDIR)/$(MODULE).a: $(OBJ) | $(DIRS:%=ALL--%)
 	@# Recreate archive to cleanup deleted/non selected source files objects
 	$(Q)$(RM) $@
-	$(Q)$(AR) $(ARFLAGS) $(foreach f,$(abspath $@ $^),$(call relpath,$f))
+	$(Q)$(AR) $(ARFLAGS) $(foreach f,$(abspath $@ $^),$(call relpath,$(abspath .),$f))
 
 CXXFLAGS = $(filter-out $(CXXUWFLAGS), $(CFLAGS)) $(CXXEXFLAGS)
 CCASFLAGS = $(filter-out $(CCASUWFLAGS), $(CFLAGS)) $(CCASEXFLAGS)
@@ -99,6 +97,9 @@ $(ASMOBJ): $(BINDIR)/$(MODULE)/%.o: %.s
 $(ASSMOBJ): $(BINDIR)/$(MODULE)/%.o: %.S $(RIOTBUILD_CONFIG_HEADER_C)
 	$(Q)$(CCAS) $(CCASFLAGS) $(INCLUDES) -MD -MP -c -o $@ $(abspath $<)
 
+# Include utility library
+include $(RIOTMAKE)/utils.inc.mk
+
 # pull in dependency info for *existing* .o files
 # deleted header files will be silently ignored
 -include $(DEP)

Makefile.include

@@ -457,6 +457,41 @@ print-size: $(ELFFILE)
 
 endif # BUILD_IN_DOCKER
 
+# Rules to check the correctness of thin archives.
+
+# Each ARCHECK file contains all the absolute paths found inside the archive.
+BASELIB_ARCHECKS = $(patsubst %.a,%.a-check,$(filter %.a,$(BASELIBS)))
+
+# For each a file, print the absolute paths found inside it
+# If "ar t" is called with an absolute path it will print an abs path regardless
+# of how the archive is internally
+# In case of a malformed archive, ar prints to stderr (and sets an error code).
+# Doing `2>&1` is hacky, the correct thing would be to get the exit code.
+# The `| %.a` is necessary to be able to check file produced in docker.
+%.a-check: %.a
+	$(Q)$(AR) t $(call relpath_here,$<) 2>&1 | grep '^/' | '$(LAZYSPONGE)' $(LAZYSPONGE_FLAGS) '$@'
+
+ARCHIVE_CHECK = $(BINDIR)/$(APPLICATION).archive-check
+
+$(ARCHIVE_CHECK): $(BASELIB_ARCHECKS)
+	$(Q)cat $^ | '$(LAZYSPONGE)' $(LAZYSPONGE_FLAGS) '$@'
+
+# Rule to check if thin archives are correctly produced, that is, with a correct
+# relative path.
+ifeq ($(BUILD_IN_DOCKER),1)
+archive-check: ..in-docker-container
+else
+archive-check: $(ARCHIVE_CHECK) FORCE
+	@if [ -s '$<' ] ; then \
+		$(COLOR_ECHO) '$(COLOR_RED)Found the following absolute paths in archives' ;\
+		cat '$<';\
+	elif [ -f '$<' ] ; then \
+		$(COLOR_ECHO) '$(COLOR_GREEN)Archives correctly formed' ;\
+	else \
+		$(COLOR_ECHO) '$(COLOR_RED)Unexpected error (file not found)' ;\
+	fi
+endif # BUILD_IN_DOCKER
+
 # Check given command is available in the path
 #   check_cmd 'command' 'description'
 define check_cmd
@@ -709,6 +744,9 @@ CFLAGS := $(patsubst -D%,,$(CFLAGS))
 CFLAGS := $(patsubst -U%,,$(CFLAGS))
 CFLAGS += -include '$(RIOTBUILD_CONFIG_HEADER_C)'
 
+# include utility library
+include $(RIOTMAKE)/utils.inc.mk
+
 # include mcuboot support
 include $(RIOTMAKE)/mcuboot.mk
 

makefiles/docker.inc.mk

@@ -8,6 +8,7 @@ export DOCKER_MAKECMDGOALS_POSSIBLE = \
   scan-build \
   scan-build-analyze \
   tests-% \
+  archive-check \
   #
 export DOCKER_MAKECMDGOALS = $(filter $(DOCKER_MAKECMDGOALS_POSSIBLE),$(MAKECMDGOALS))
 

makefiles/utils.inc.mk

@@ -83,3 +83,5 @@ test-relpath-negtive:
 	echo $(call relpath,/,/)
 	echo $(call relpath,/1/2/3,/1/2/3)
 
+# Return a path relative to the current directory
+relpath_here = $(call relpath,$(abspath .),$(abspath $(1)))