docs: Summarise directory reference syntaxes, permute

[secnet.git] / README

diff --git a/README b/README
index 0ab3b50057b5ed23172f7fa60b911fd8c9d47e23..5a585df4f26d3a1f042622712aec99232994edc0 100644 (file)
--- a/README
+++ b/README
@@ -138,6 +138,19 @@ 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
+---------------------------------------
+
+                  In build tree             In source tree             
+                  Relative  Absolute        Relative     Absolute      
+                                          
+                  &file     $(abs)/&file                             
+ This directory   &/file    $(abs)/&/file   &^/file      &~/file       
+                  & f g h                   & ^ f g h    & ~ f g h     
+                                          
+ Top level        file      $(abs)/file     $(ts)/file   $(ats)/file   
+                  f g h                                              
+
 Substitution syntax
 -------------------
 
@@ -282,15 +295,18 @@ 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.
+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 there is no
-separate-directory barrier stopping the different invocations ending
-up trying to make the same targets at the same time, which causes
-hideous racy lossage.  There are ways to get this to work reliably but
-it is advanced stuff.
+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