MESSAGE
| DATE | 2021-01-31 |
| FROM | Gavin Smith
|
| SUBJECT | Re: [Hangout - NYLXS] Future plans for Autotools
|
On Mon, Jan 25, 2021 at 03:15:47PM -0800, Paul Eggert wrote:
> On 1/25/21 2:59 PM, Gavin Smith wrote:
> > Does this
> > work or does GNU make have other ways of doing this? (It would be
> > better if it could be done without communicating via files.) Is there
> > any way to set a Makefile variable from within a rule and then depend upon
> > that variable being set in other rules?
>
> GNU Make supports variables defined via ::=, and an earlier section of a GNU
> makefile could compute CC and assign to it that way. This would handle the
> simple case you gave. Unfortunately there are other cases that would require
> intermediate files with current GNU Make. Still, the overhead in using files
> would be worth it (at least for me) if we could use make -j.
>
> The ::= feature was added to POSIX ten years ago or so, so it could even be
> used in Makefiles intended to be portable to other new-enough
> POSIX-compatible platforms. It wouldn't work on older platforms, though.
Another issue is how to record the results of tests from a a Makefile.
With autoconf, autoconf variables are recorded with AC_CONFIG_FILES
and AC_CONFIG_HEADERS. Presumably the same would have to be done,
substituting in an output file with the values of these variables.
However, there can be many hundreds of them (just look at a Makefile.in
file). As far as I can tell, there isn't an easy way to export
hundreds of Makefile variables to a process. Is there some feature or
trick I'm missing?
You could build up a long command line, but it could end up being
extremely long. The code below shows how this could be done with
GNU Make (for just 3 variables). The substitution step would need to
be done after all the variables had been set, unless there was some
kind of locking/synchronisation to allow Makefile rules to record
configuration variables in parallel. It's possible to create a
small file for every variable but this would lead to hundreds of
small files being created.
VARS::=
VARS::=$(VARS) A=$$(A)
set-A:
$(eval A ::= $(shell echo 1))
VARS::=$(VARS) B=$$(B)
set-B:
$(eval B ::= $(shell echo 2))
VARS::=$(VARS) C=$$(C)
set-C:
$(eval C ::= $(shell echo 3))
finish-configure: set-A set-B set-C
$(eval EXVARS=$(VARS))
export $(EXVARS) ; echo "$$A $$B $$C"
_______________________________________________
Hangout mailing list
Hangout-at-nylxs.com
http://lists.mrbrklyn.com/mailman/listinfo/hangout
|
|
