X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=cfd7ad03d1853cc3b8e68b6847ee1df079d401ca;hp=b22927beace665887ce11e60810a4f1c73d09112;hb=c0b216c79763f720df20e002fc14c9348a0e05c2;hpb=3d411362b8d7c28f0faea3aef1c424f5696f561c diff --git a/README b/README index b22927b..cfd7ad0 100644 --- a/README +++ b/README @@ -28,15 +28,17 @@ Basic approach 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 @@ -83,7 +85,7 @@ individual targets (as specified according to their dependencies). You can define other per-directory recursive targets too: simply mention (usually, by setting) the variable &TARGETS_zonk, or whatever. -This will create a src/zonk target. +This will create a src/zonk target (for appropriate value of src/). Unlike `all', these other targets only exist in areas of the project where at least something mentions them. So for example, if &TARGETS_zonk is mentioned in src but not lib, `make zonk' in @@ -103,6 +105,19 @@ is already provided in subdirmk, for you to reference like this: &: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 ------------------ @@ -138,6 +153,47 @@ 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. +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 ------------------- @@ -163,22 +219,37 @@ empty string). 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 +&;/ => $(top_srcdir)/ + +In general: + = return subdir without delimiter (not allowed with `,' `;') + , pathname of this subdirectory in source tree + ; pathname of top level of source tree + / terminates the escape (needed if next is not lwsp or space) + lwsp starts multi-word processing (see below) + +So pathname syntax is a subset of: + '&' [ ',' | ';' ] [ lc | '/' ] && => && for convenience in shell runes \& => & general escaping mechanism & thing thing... & -& ^ thing thing... & -& ~ thing thing... & +&, thing thing... & +&; thing thing... & Convenience syntax for prefixing multiple filenames. - Introduced by & followed by lwsp (space or tab). - Each lwsp-separated non-ws word is prefixed by &/ &^/ &~/ - respectively. No other & escapes are recognised. + Introduced by & followed by lwsp where lc could go. + Each lwsp-separated non-ws word is prefixed by &/ etc. + etc. respectively. No other & escapes are recognised. This processing continues until & preceded by lwsp, or until EOL (the end of the line), or \ then EOL. @@ -193,7 +264,7 @@ empty string). &! disables & until EOL (and then disappears) &# delete everything to end of line - (useful if the RHS contains unrecognise & constructions) + (useful if the RHS contains unrecognised & constructions) &!STUFF changes the escape sequence from & to literally STUFF @@ -275,6 +346,31 @@ have: &:include subdirmk/cdeps.sd.mk &:include subdirmk/clean.sd.mk +Hints +----- + +You can convert your project incrementally. Start with the top-level +Makefile.in and rename it to Subdir.sd.mk, and add the appropriate +stuff to configure.ac, and fix everything up. Leave the existing +$(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 -----------------