X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=secnet.git;a=blobdiff_plain;f=subdirmk%2Fcdeps.sd.mk;h=5a2bfb28df5bf2737c2c556eac31b1090c7b41db;hp=aeb35bf88427385246cf02a841b544325f22d9c1;hb=95bcfc013b7ec7ccf60e522409d71daa7464a2ee;hpb=21f1f96d711d4e745a87bc1561143887c02f1031

diff --git a/subdirmk/cdeps.sd.mk b/subdirmk/cdeps.sd.mk
index aeb35bf..5a2bfb2 100644
--- a/subdirmk/cdeps.sd.mk
+++ b/subdirmk/cdeps.sd.mk
@@ -1,5 +1,26 @@
+# subdirmk - useful rules for making and using cpp .*.d files
+#  Copyright 2019 Mark Wooding
+#  Copyright 2019 Ian Jackson
+# SPDX-License-Identifier: LGPL-2.0-or-later
 
-&DEPFILES += $(foreach b,$(patsubst %.o,%,$(&OBJECTS)), \
+&# Usage:
+&#   &:include subdirmk/cdeps.sd.mk
+&# (probably in Perdir.sd.mk)
+&#
+&# Arranges for automatic #include dependency tracking for
+&# C compilation.  The compiler is asked to write the dependencies to
+&#  .*.d and these are automatically included.
+&#
+&# There is a bug: if a #included file is deleted and all references
+&# in .c files to it removed, `make' will complain that it is needed
+&# and can't be built.  `make clean' will fix this.
+
+CDEPS_CFLAGS ?= -MD -MF $(*D)/.$(*F).d
+
+&CDEPS_OBJECTS += $(&OBJECTS)
+
+&DEPFILES += $(foreach b,$(patsubst %.o,%,$(&CDEPS_OBJECTS)), \
 		$(dir $b).$(notdir $b).d)
 -include $(&DEPFILES)
 
+&CLEAN += $(&DEPFILES)