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Re: Naming object files according to target

From: Philip Guenther
Subject: Re: Naming object files according to target
Date: Sun, 3 May 2009 17:21:46 -0700

On Sun, May 3, 2009 at 11:25 AM, t-timmy <address@hidden> wrote:
> I want to name each of my object files prefixed with the current target
> name. That way when I change targets, I won't have to recompile everything to
> make sure there is no residue from the previous compilation (which may have 
> been
> for a different target).
> For example:
> target1: c_flags = -DSOMETHING
> target1: main.o
> target2: c_flags = -DSOMETHING_ELSE
> target2: main.o
> main.o:
> gcc $(c_flags) etc...

No, that isn't an example of what you want, because that doesn't use
prefixes like you want.  As is, you didn't give us enough to go on.
You don't show any rules for linking programs, so saying "make
target1" will compile main.o but *not* create a program from it, which
is almost certainly not what you want, but we can't tell whether "make
target1" should build a program "target1" from main.o or whether it
should build "target1-someprogram" from main.o

Next, you show main.o with an explicit rule.  Really?  You give each
.o an explicit rule instead of using pattern rules?  Why?  If you
actually have a real reason to do that (how can we tell?) then that'll
affect what solutions are appropriate.

> The only way I can avoid recompiling every time is by manually making a rule
> for, let's say, target1-main.o and target2-main.o, but I have a lot of
> source files and it's a real hassle.

Make give you at least two different ways to let you use the same rule
for the two targets.  You almost certainly only one of the following;
you'll need to decide which though the former is probably simpler.

1) target-specific variable assignments.  As described in the info
pages, such a setting
   is propagated to all the prerequisites of the target, so setting
CFLAGS for target1
   will mean that it'll be set for the files target1 depends
on...which would presumably
   be things like target1-main.o

2) automatic variables.  These are the variables like $@ and $^ that
are set for you
   by make with values that depend on the rule involved.  You can use
the same rule
   for both target1-main.o and target2-main.o and example $@ in the commands to
   figure out which settings to use.

Philip Guenther

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