The developer is expected to write a makefile fragment, in each
relevant subdirectory, called `Subdir.sd.mk'.
-These fragments may contain ordinary make language.
+These fragments may contain ordinary make language. Unqualified
+filenames are relative to the build toplevel, and all commands all run
+there.
However, the sigil & is treated specially. By and large, it refers to
-`the current directory'. There are a variety of convenient
-constructions.
+`the build directory corresponding to this .sd.mk file', etc.
+There are a variety of convenient constructions.
The result is that to a large extent, the Subdir.sd.mk has an easy way
to namespace its "local" make variables, and an easy way to refer to
-its "local" filenames.
+its "local" filenames (and filenames in general).
The Subdir.sd.mk's are filtered, fed through autoconf in the usual way
(for @..@-substitutions) and included by one autogenerated toplevel
&:include subdirmk/clean.sd.mk
For example you could put that in Perdir.sd.mk.
+The top-level Subdir.sd.mk is the first makefile included after the
+autogenerated `main.mk' which merely has some basic settings and
+includes. So if you want to get in early and set global variables,
+put them near the top of Subdir.sd.mk.
+
+subdirmk's filter script itself sets (only) these variables:
+ top_srcdir
+ abs_top_srcdir
+ SUBDIRMK_MAKEFILES
+ MAKEFILE_TEMPLATES
+You are likely to want to define $(PWD), and shorter names for
+top_srdir and abs_top_srcdir (we suggest $(src) and $(abs_src)).
+
Global definitions
------------------
automatic regeneration for all of this template substitution, and for
config.status etc. is done for you.
+Tables of file reference syntaxes
+---------------------------------
+
+In a nonrecursive makefile supporting out of tree builds there are
+three separate important distinctions between different file
+locations:
+
+ (i) In the build tree, or in the source tree ?
+
+ (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
+ relates, or relative to the project's top level ?
+
+ (iii) Absolute or relative pathname ? Usually relative pathnames
+ suffice. Where an absolute pathname is needed, it can be built
+ out of &/ and an appropriate make variable such as $(PWD).
+
+Path construction &-expansions are built from the following:
+
+ Relative paths in...
+ build source
+
+ This directory & &^
+ Top level . &~
+
+In more detail, with all the various options laid out:
+
+ Recommended Relative paths in... Absolute paths in...
+ for build source build source
+
+ This lc &file &^file $(PWD)/&file $(abs_src)/&file
+ directory any &/file &^/file $(PWD)/&/file $(abs_src)/&/file
+ several & f g h &^ f g h $(addprefix...)
+
+ Top lc file &~file
+ level any file &~/file $(PWD)/file $(abs_src)/file
+ .mk.in file $(src)/file $(PWD)/file $(abs_src)/file
+ several f g h &~ f g h $(addprefix...)
+
+(This assumes you have appropriate make variables src, PWD and
+abs_src.)
+
Substitution syntax
-------------------
variables usually uppercase. Otherwise, use another syntax:
&_ => sub_dir_ or TOP_
-&/ => sub/dir/ or nothing
&=_ => sub_dir or TOP
+
+&/ => sub/dir/ or nothing
&=/ => sub/dir or .
-&^ => $(top_srcdir)/sub/dir or $(top_srcdir)
-&~ => $(abs_top_srcdir)/sub/dir or $(abs_top_srcdir)
+
+&^lc => $(top_srcdir)/sub/dir/lc
+&^/ => $(top_srcdir)/sub/dir/
+
+&~lc => $(top_srcdir)/lc
+&~/ => $(top_srcdir)/
+
+In general:
+ = return subdir without delimiter (not allowed with `^' `~')
+ ^ pathname of this subdirectory in source tree
+ ~ pathname of top level of source tree
+ / terminates the escape (needed if next is not lwsp or space)
+ lwsp starts multi-word processing (see below)
+
+So pathname syntax is a subset of:
+ '&' [ '^' | '~' ] [ lc | '/' ]
&& => && for convenience in shell runes
\& => & general escaping mechanism
& thing thing... &
-& ^ thing thing... &
-& ~ thing thing... &
+&^ thing thing... &
+&~ thing thing... &
Convenience syntax for prefixing multiple filenames.
- Introduced by & followed by lwsp (space or tab).
- Each lwsp-separated non-ws word is prefixed by &/ &^/ &~/
- respectively. No other & escapes are recognised.
+ Introduced by & followed by lwsp where lc could go.
+ Each lwsp-separated non-ws word is prefixed by &/ etc.
+ etc. respectively. No other & escapes are recognised.
This processing continues until & preceded by lwsp,
or until EOL (the end of the line), or \ then EOL.
&# delete everything to end of line
(useful if the RHS contains unrecognised & constructions)
-&!STUFF
+&:changequote STUFF
changes the escape sequence from & to literally STUFF
STUFF may be any series of of non-whitespace characters,
- and is terminated by EOL or lwsp. &!STUFF and the lwsp
- are discarded.
+ and is terminated by EOL or lwsp. The whole line is
+ discarded.
After this, write STUFF instead of &, everywhere.
The effect is global and lasts until the next setting.
it back before using &:include.
Notably
- STUFFSTUFF => STUFFSTUFF
- \STUFF => STUFF
- STUFF!& set escape back to &
+ STUFFSTUFF => STUFFSTUFF
+ \STUFF => STUFF
+ STUFF:changequote & => set escape back to &
&TARGETS_things
Handled specially. If mentioned, declares that this
far enough to regenerate a working set of makefiles. If this happens
just rerun ./config.status by hand.
+If you go back and forth between different versions of your code you
+can sometimes find that `make' complains that one of your Subdir.sd.mk
+files is missing: typically, if iot was used and therefore a
+dependency in some other version of your code. If you run `make
+clean' (or `make realclean') these dependencies are suppressed, which
+will clear up the problem.
+
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