Re: [RFC/CFT] Separate obj/src dir

[Daniel Jacobowitz <dan@debian.org>]

On Tue, Nov 19, 2002 at 03:46:28PM -0500, Richard B. Johnson wrote:
> On Tue, 19 Nov 2002, Sam Ravnborg wrote:
> 
> > On Tue, Nov 19, 2002 at 03:22:45PM -0500, Richard B. Johnson wrote:
> > > I have a question; "What problem is this supposed to solve?"
> > 
> > Two problems (at least):
> > 
> > 1) You want to compile your kernel based on two different configurations,
> > but sharing the same src. No need to have a duplicate of all src.
> > - There are other ways to do this using symlinks
> > 
> > 2) You have the src located on a read-only filesystem.
> > I have been told this is the case for some SCM systems.
> > 
> > People has requested this feature at several occasions, and here
> > it is based on the current build system.
> > It's not ready for inclusion (obviously), and you shall
> > also see this as a way to check that this is considered usefull
> > by someone.
> > 
> > 	Sam
> 
> Hmmm. If your source is located on a read-only file-system, you
> can't modify it. You are therefore doomed to use only "known working"
> distributions that are known to work with all possible module
> combinations (these don't exist). So you get to compile the kernel
> just as a test exercise or a gimmick like; "what did you do today?..."
> answer; "I compiled the kernel..." This seems to not be very practical
> since the purpose of compiling the kernel was to add something or
> fix something. Now, its just to see if it compiles.
> 
> Different configurations are handled with different ".config"
> files.
> 
> I think all you did was increase the compile time by writing
> output files to different directories than the ones currently
> in cache. There are a lot of negatives. It would be a shame for
> you to waste a great deal of time on something that would not
> be accepted into the distribution. Remember the earlier `make modules`
> where the new objects went into a separate directory with sym-links?
> That got changed. I think it got changed for good reasons.

There are plenty of other good reasons for this.  Offhand:

- Speeds up grepping through the source tree for things if you don't
have to look at object files.  SCCS dirs still make this a pain, I may
hack grep -r to optionally skip them.

- Guarantees that doing a build should not affect anything in the srcdir;
this is handy when preparing release tarballs etc.

- Multiple builds from the same source (different architectures,
configs, compilers, whatever) without copying the source.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer