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.
-Summary of recommended directory reference syntaxes
----------------------------------------------------
+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 ?
-Path construction &-expansions, meanings summary:
+ (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
+ relates, or relative to the project's top level ?
- In build tree In source tree
- This directory just & &,
- Top level &. implies absolute &;
+ (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).
-Adding `@' means "absolute path". This is not needed with &. because
-there is never any need to use &. since it would expand to nothing.
-`/' terminates the escape (needed if the next thing is not a lowercase
-character, or space). `=' means "just the value, no /". Space starts
-multi-word processing.
+Path construction &-expansions are built from the following:
- 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
+ Relative paths in...
+ build source
+
+ This directory & &^
+ Top level . &~
- Top lc &.file &;file &@;file
- level any file &./file &;/file &@;/file
- several f g h &. f g h &; f g h &@; f g h
- .mk.in file $(abs)/file $(src)/file $(abs_src)/file
+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
-------------------
The assumption is that filenames are usually lowercase and
variables usually uppercase. Otherwise, use another syntax:
-&_ => sub_dir_ or TOP_
-&=_ => sub_dir or TOP
-
&/ => sub/dir/ or nothing
-&=/ => sub/dir or .
-
-&,lc => $(top_srcdir)/sub/dir/lc
-&,/ => $(top_srcdir)/sub/dir/
-
-&;lc => $(top_srcdir)/sub/dir/lc
-&;/ => $(top_srcdir)/sub/dir/
-
-&@lc => $(PWD)/sub/dir/lc
-&@/ => $(PWD)/sub/dir/
+&_ => sub_dir_ or TOP_
+&. => sub/dir or .
+ (This implies that `&./' works roughly like `&/', although
+ it can produce a needless `./')
-&.lc => $(PWD)/lc
-&./ => $(PWD)/
+&= => sub_dir or TOP
-&@,lc => $(abs_top_srcdir)/sub/dir/lc
-&@,/ => $(abs_top_srcdir)/sub/dir/
+&^lc => $(top_srcdir)/sub/dir/lc
+&^/ => $(top_srcdir)/sub/dir/
+&^. => $(top_srcdir)/sub/dir
-&@;lc => $(abs_top_srcdir)/sub/dir/lc
-&@;/ => $(abs_top_srcdir)/sub/dir/
+&~lc => $(top_srcdir)/lc
+&~/ => $(top_srcdir)/
+&~. => $(top_srcdir)
In general:
- = return subdir without delimiter (not allowed with `,' `;' `@')
- , pathname of this subdirectory in source tree
- ; pathname of top level of source tree
- . pathname of this directory in build tree, implies absolute pathnames
- @ absolute pathnames (forbidden with `.', must come first)
+ ^ pathname of this subdirectory in source tree
+ ~ pathname of top level of source tree
+ / terminates the path escape } needed if next is
+ _ terminates the var escape } not lwsp or space)
+ . terminates path escape giving dir name (excluding /)
+ = terminates var escape giving only prefix part (rarely needed)
+ lwsp starts multi-word processing (see below)
So pathname syntax is a subset of:
- '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ]
-
- To avoid incomprehensible .sd.mk files, some combinations are not
- allowed. For example `&@=./' would mean `$(PWD)/sub/dir' but can
- be spelled `$(PWD)/&=/', but more normally the trailing / can be
- tolerated, so use `&@/'.
+ '&' [ '^' | '~' ] [ lc | '/' | '.' | '=' ]
&& => && for convenience in shell runes
-\& => & general escaping mechanism
+
+&\& => & general escaping mechanism
+&\$ => $
+
+&$VARIABLE => $(sub_dir_VARIABLE) or $(TOP_VARIABLE)
+ VARIABLE is ASCII starting with a letter and matching \w+
& thing thing... &
-&. thing thing... & &@. thing thing... &
-&, thing thing... & &@, thing thing... &
-&; thing thing... & &@; thing thing... &
+&^ thing thing... &
+&~ thing thing... &
Convenience syntax for prefixing multiple filenames.
Introduced by & followed by lwsp where lc could go.
- Each lwsp-separated non-ws word is prefixed by &/ &./ &@./
+ 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.
recognised at start of line only (possibly after lwsp)
args are processed for &
-&:include filename filename should usually be foo.sd.mk
+&:include filename filename should usually be [&]foo.sd.mk
&:-include filename tolerate nonexistent file
filenames are relative to $(top_srcdir)
+ RHS is &-expanded
&!<lwsp> disables & until EOL (and then disappears)
&# delete everything to end of line
(useful if the RHS contains unrecognised & constructions)
-&!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.
+&:changequote NEWQUOTE
+ changes the escape sequence from & to literally NEWQUOTE
+ NEWQUOTE may be any series of of non-whitespace characters,
+ and is terminated by EOL or lwsp. The whole line is
+ discarded.
- After this, write STUFF instead of &, everywhere.
+ After this, write NEWQUOTE instead of &, everywhere.
The effect is global and lasts until the next setting.
It takes effect on &:include'd files too, so maybe set
it back before using &:include.
Notably
- STUFFSTUFF => STUFFSTUFF
- \STUFF => STUFF
- STUFF!& set escape back to &
+ NEWQUOTENEWQUOTE => NEWQUOTENEWQUOTE
+ NEWQUOTE\NEWQUOTE => NEWQUOTE
+ NEWQUOTE:changequote & set escape back to &
&TARGETS_things
- Handled specially. If mentioned, declares that this
+ Handled specially. If mentioned at the start of a line
+ (possibly following whitespace), declares that this
subdir ought to have a target `things'. The rule will be
&/things:: $(&TARGETS_things)
which recursively implies this directory's `things'.
Must be spelled exactly &TARGETS_things. &_TARGETS_things,
- for example, is not magic. But mentioning &TARGETS_things in
- a #-comment *does* work because the & filter does not care
- about comments.
+ for example, is not magic. To make the target exist
+ without providing any prerequisites for it, write a line
+ containing just `&TARGETS_things +='.
`all' is extra special: every directory has an `all'
target, which corresponds to &TARGETS.
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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