Re: makefile compilation question

[NICOLE Remi via Tech-talk <tech-talk at aps.anl.gov>]

This rule is a "static pattern rule"[1], it allows specifying multiple
targets, while also pattern matching with "%".

[1]:
https://www.gnu.org/software/make/manual/html_node/Static-Usage.html

Suppose we have 'DIRS = dir1'. Expanded, this rule looks like this:

    # Targets
    linux-x86_64 \
      inc build install ... \
      inc.linux-x86_64 build.linux-x86_64 install.linux-x86_64 \
        # Pattern match with "%" \
        :%: \
          # Dependencies \
          dir1.%


- 'linux-x86_64' comes from ARCH
- 'inc build install ...' comes from ACTIONS
- 'inc.linux-x86_64 build.linux-x86_64 install.linux-x86_64' comes from
actionArchTargets

If we run 'make install', this will match this rule, since install is
in it. Then make will pattern match the target 'install' with '%',
which matches everything.

make then looks up dependencies for the target 'install', which is 
'dir1.%', which gets replaced with 'dir1.install'.

Afterwards, we go into the other rule I mentionned, which gets expanded
to something like this:

    # Targets
    dir1 \
      dir1.inc dir1.build dir1.install ... \
      dir1.linux-x86_64 \
      dir1.inc.linux-x86_64 dir1.build.linux-x86_64 ...: \
        # Recipe
        #            ,--- Fetches the dir part of the target
        #          vvvvvvvvvv
        $(MAKE) -C $(dirPart) $(actionArchPart)
        #                     ^^^^^^^^^^^^^^^^^
        #                            |
        # Fetches the action part of the target


-- 
Rémi NICOLE <remi.nicole at cea.fr>
CEA/DRF/IRFU/DIS/LDISC

On Tue, 2023-05-23 at 01:37 +0800, timesir wrote:
> hello,
>     I still don't understand it very well, please explain it in
> detail. Especially 
> 
> beforeActions = $(addprefix before-,$(ACTIONS))
> $(beforeActions):
> $(ARCHS) $(ACTIONS) $(actionArchTargets) :%: \
>     $(foreach dir, $(DIRS), $(dir)$(DIVIDER)%)
> 
> NICOLE Remi via Tech-talk <tech-talk at aps.anl.gov> 于2023年5月22日周一
> 19:23写道：
> > Hey there!
> > 
> > From my understanding:
> > 
> > In epics-base/configure/RULES_DIR, you will find:
> > 
> >     $(DIRS) $(dirActionTargets) $(dirArchTargets)
> > $(dirActionArchTargets):
> >         $(MAKE) -C $(dirPart) $(actionArchPart)
> > 
> > which makes it so that 'make myApp.install' will run 'make -C myApp
> > install'.
> > 
> > and
> > 
> >     $(ARCHS) $(ACTIONS) $(actionArchTargets) :%: \
> >         $(foreach dir, $(DIRS), $(dir)$(DIVIDER)%)
> > 
> > will make it so that 'install' depends on every '$(dir).install'
> > 
> > Then, in epics-base/configure/RULES, it includes RULES_ARCH, which
> > conceptually "splits" the build for every wanted architecture,
> > which
> > then re-includes RULES but the second time, it goes into
> > RULES_BUILD,
> > which defines rules for building libraries, executables, and so on
> > for
> > the specified architecture (T_A).
> > 
> > Hope it helps.
> >