Re: Patch to allow configure out-with source directory

[Rich Felker <dalias@libc.org>]

On Wed, Mar 04, 2015 at 05:52:30PM +0100, Laurent Bercot wrote:
> On 04/03/2015 17:41, Rich Felker wrote:
> >Could you clarify what problem it solves? I don't think this is
> >anywhere near sufficient to support out-of-tree builds. That's a
> >difficult problem which nsz worked on in the past but didn't complete
> >because we kept running into corner cases that broke.
> 
>  Is there a discussion archive or some log of that attempt and the
> problems you ran into ?
> 
>  I shamelessly stole the musl Makefile's design to use in my
> software - I hardly knew the make language at the time, and wanted
> to study a small and clean case - and was considering implementing
> out-of-tree builds at some point in the (distant) future. If there
> were some notes describing the obstacles you faced, it would help
> me when I get to it - or more likely convince me, like it
> apparently convinced you, that it's just not worth it.

The first problem you face is how the implicit rules are written,
especially the ones for asm files that replace C files. They depend on
make's implicit application of leading directories. But I'm pretty
sure nsz had this worked out clearly and it was more subtle corner
cases that kept biting. He could probably explain better.

Another issue I recall is the presence of generated include files and
the bits symlink in the include tree. This is part of the build
process I want to revisit/change anyway when refactoring the bits
headers to reduce duplication, so understanding the obstacles to
out-of-tree builds before getting started with that would be a big
help.

Rich