X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=5bfb29ebdecf5cfdd00246e8319427a04464c4b9;hp=e5ef4b4f5c28a1291e1d4b9c4e981d1ffb4f4eb7;hb=10b511fc2feaaf18a62eeb57087c2527ff71ce11;hpb=f1789a0ae66174a95c8d629738eae98d40c084ac

diff --git a/README b/README
index e5ef4b4..5bfb29e 100644
--- a/README
+++ b/README
@@ -138,6 +138,21 @@ If you `include subdirmk/regen.mk', dependency management and
 automatic regeneration for all of this template substitution, and for
 config.status etc. is done for you.
 
+Summary of directory reference syntaxes
+---------------------------------------
+
+      Recommended     In build tree             In source tree
+             when     Relative  Absolute        Relative     Absolute
+                                          
+  This       lc       &file     &~file          &^file       &^~file
+  directory  any      &/file    &~/file         &^/file      &^~/file
+             several  & f g h   & ~ f g h       & ^ f g h    & ^~ f g h
+
+  Top        lc                 &@~file         &@^file      &@~^file
+  level      any      file      &@~/file        &@^/file     &@~^/file
+             .mk.in   file      $(abs)/file     $(src)/file  $(abs_src)/file
+             several  f g h     & @~ f g h      & @^ f g h   & @~^ f g h
+
 Substitution syntax
 -------------------
 
@@ -169,6 +184,11 @@ empty string).
 &^		=>	$(top_srcdir)/sub/dir		or $(top_srcdir)
 &~		=>	$(abs_top_srcdir)/sub/dir	or $(abs_top_srcdir)
 
+In general:
+        ^       filenames in source tree rather than build tree
+        ~       filenames are absolute rather than relative
+        @       filenames do not contain subdir (useful with the above)
+
 &&		=>	&&		for convenience in shell runes
 \&		=>	&		general escaping mechanism
 
@@ -275,6 +295,31 @@ have:
   &:include subdirmk/cdeps.sd.mk
   &:include subdirmk/clean.sd.mk
 
+Hints
+-----
+
+You can convert your project incrementally.  Start with the top-level
+Makefile.in and rename it to Subdir.sd.mk, and add the appropriate
+stuff to configure.ac, and fix everything up.  Leave the existing
+$(MAKE) -C for your existing subdirectories alone.  Then you can
+convert individual subdirectories, or classes of subdirectories, at
+your leisure.  (You must be /sure/ that each subdirectory will be
+entered only once at a time, but your existing recursive make descent
+system should already do that or you already have concurrency bugs.)
+
+Aside from this, be very wary of any invocation of $(MAKE) anywhere.
+This is a frequent source of concurrency bugs in recursive make build
+systems.  When combined with nonrecursive make it's all in the same
+directory and there is nothing stopping the different invocations
+ending up trying to make the same targets at the same time. That
+causes hideous racy lossage.  There are ways to get this to work
+reliably but it is advanced stuff.
+
+If you make syntax errors, or certain kinds of other errors, in your
+makefiles, you may find that just `make' is broken now and cannot get
+far enough to regenerate a working set of makefiles.  If this happens
+just rerun ./config.status by hand.
+
 
 Legal information
 -----------------