[Mesa-dev] [PATCH] Mesa: Fix a race in the build

[Mike Frysinger]

On Tue, Jun 12, 2012 at 6:47 PM, Dan Nicholson <dbn.lists at gmail.com> wrote:

> On 6/12/12, Stéphane Marchesin <marcheu at chromium.org> wrote:
> > From: Mike Frysinger <vapier at chromium.org>
> >
> > The intent of the message above it is right (we need to build those
> > dependencies in that order) but the implementation is wrong, as it
> > can be executed in any order. To enforce the order, invoke make
> > multiple times.
> > ---
> >  src/mesa/Makefile |    8 ++++++--
> >  1 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/mesa/Makefile b/src/mesa/Makefile
> > index b0b461f..c436890 100644
> > --- a/src/mesa/Makefile
> > +++ b/src/mesa/Makefile
> > @@ -33,8 +33,12 @@ MESA_CXXFLAGS := $(LLVM_CFLAGS) $(CXXFLAGS)
> >       $(CC) -c -o $@ $< $(MESA_CPPFLAGS) $(MESA_CFLAGS)
> >
> >  # Default: build dependencies, then asm_subdirs, GLSL built-in lib,
> > -# then convenience libs (.a) and finally the device drivers:
> > -default: $(DEPENDS) asm_subdirs $(MESA_LIBS) driver_subdirs
> > +# then convenience libs (.a) and finally the device drivers.
> > +# To ensure ordering, we have to invoke make each time:
> > +default: $(DEPENDS)
> > +     $(MAKE) asm_subdirs
> > +     $(MAKE) $(MESA_LIBS)
> > +     $(MAKE) driver_subdirs
> >
> >  .PHONY: main/git_sha1.h.tmp
> >  main/git_sha1.h.tmp:
>
> The alternative that's more correct is to encode the dependencies in
> the right locations. I.e., make $(DEPENDS) a prereq for asm_subdirs,
> asm_subdirs as prereq for $(MESA_LIBS), etc. That enforces the order
> in the correct place and allows you to do something like "make
> driver_dirs" and have it work correctly. Some of that is already
> there, and it would be useful to know which part is racing. I suppose
> if no one is going to do that work, though...
>

the trouble is that w/out GNU make, you can't declare a dependency as
order-only.  so by having $(MESA_LIBS) depend on asm_subdirs (which is a
PHONY target), things end up getting regenerated all the time.

i picked this as the portable and least crappy solution.  if you can make
it work otherwise, SGTM :).
-mike
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