Re: [Qemu-trivial] [Qemu-devel] [PATCH 2/2] Makefile: use full path for qapi-generated directory

[Stefano Stabellini]

On Thu, 1 Dec 2011, Anthony Liguori wrote:
> On 12/01/2011 12:11 PM, Stefan Weil wrote:
> > Am 01.12.2011 16:19, schrieb Stefano Stabellini:
> >> On Wed, 30 Nov 2011, Stefan Weil wrote:
> >>> It's common to use either out-of-tree builds or in-tree builds,
> >>> but not to mix both variants with a common root directory.
> >>> I think QEMU should explicitly forbid that mixed scenario (like
> >>> other projects do).
> >>>
> >>> Even with your fix there can remain problems with generated
> >>> header files.
> >>
> >> Really? Can you provide more specific details?
> >
> > Yes. Suppose different generated header files with the same name
> > exist in the source directory tree and in the build directory tree.
> >
> > Then compiler options (the order of -I options) will determine
> > which of two header files with same name will be used in out-of-tree
> > builds. If the wrong one (that from the source directory tree) is used,
> > the compiler might fail or produce wrong code (for example when
> > macro values changed).
> >>> The mixed scenario creates unnecessary complexity.
> >>> Without the mixed scenario, your patch is not needed.
> >>
> >> I agree that supporting the mixed scenario shouldn't be a priority.
> >> However without this last patch a "make clean" on the main tree is not
> >> enough to allow out of tree builds.
> >>
> >> Try the following scenario:
> >>
> >> - cd qemu; ./configure; make
> >>
> >> - make clean
> >>
> >> - cd ../temp; ./configure --source-path=../qemu; make
> >
> > Which ./configure do you run in an empty temp directory?
> > This example (like similar ones in your previous mail) won't work.
> 
> Yes, you must do external builds only from a clean source directory.  This is 
> a 
> perfectly normal requirement.  In fact, I can't think of a project that 
> doesn't 
> require this.

Fair enough.

In that case, like Michael Roth wrote, the patch "Makefile: use full
path for qapi-generated directory" doesn't actually fix anything, so
probably we don't need it either, but I'll leave it up to you.