On Fri Sep 15 01:47:31 2017, invalid.nore...@gnu.org (anonymous) wrote: [...] > Summary: Preventing infinite recursions when make is invoked from recipes
[...] > Details: > > Consider this Makefile: > > a : > echo a1 > $(MAKE) b > echo a2 > > b : > echo b1 > $(MAKE) a > echo b2 > > Building either a or b will cause infinite recursion. Yes, this is a potential issue with recursive $(MAKE) invocations, but it is not a bug. > It is possible to work around this with a template, similar to the following: > > SHELL := bash > exportable = $(shell echo $(1) | sed 's%[^[:alnum:]_]%_%g') > define make > $(eval d := $(strip $(call exportable,$(1)))) > $(eval f := $(if $(strip $(2)), -f $(realpath $(strip $2)))) > if [ "$$_making_$(d)" != "$@" ]; then \ > export _making_$(d)="$@"; \ > $(MAKE) $(f) "$(strip $(1))"; \ > fi This is a bad idea, for several reasons: 1. It uses nonportable functionality. Some of that will go away when implemented directly in C code, but not all of it. How to implement realpath for arbitrary operating systems and arbitrary file systems? If it were easy enough, GNU Make would have had it a long time ago. 2. It's a hack; there will always be cases slipping through. It is fundamentally impossible to determine whether a call to $(MAKE) is recursive just by looking at the calling syntax. E.g., realpath doesn't look at hard links. 3. There is a better way. A much simpler way to stop infinite recursion is to pass a variable indicating the recursion depth and make recursive calls conditional on its value. The $(MAKELEVEL) variable is provided for that purpose, and it has been in GNU Make for a long time, see e.g. https://ftp.gnu.org/old-gnu/Manuals/make-3.79.1/html_chapter/make_5.html#SEC50 Finally, 0. There are more reasons to avoid $(MAKE). Nonrecursive make can be faster and can track dependencies better, although it may not be wise to avoid $(MAKE) at all costs, see e.g. https://www.microsoft.com/en-us/research/wp-content/uploads/2016/03/hadrian.pdf -- Reinier Post TU Eindhoven _______________________________________________ Bug-make mailing list Bug-make@gnu.org https://lists.gnu.org/mailman/listinfo/bug-make
