Re: [Qemu-devel] [PATCH] Add CONFIG_QEMU_TIMER to handle qemu-timer-common.o dep

[Stefan Hajnoczi]

On Mon, Aug 29, 2011 at 8:27 PM, Michael Roth <address@hidden> wrote:
> @@ -380,7 +381,6 @@ else
>  trace-obj-y = trace.o
>  ifeq ($(TRACE_BACKEND),simple)
>  trace-obj-y += simpletrace.o
> -user-obj-y += qemu-timer-common.o
>  endif
>  endif

Now that we have a concrete patch to look at I think this approach is
problematic.  There are several subsystems in QEMU which might be
built outside the main qemu binary for qemu-io, qemu-img, qemu-ga,
etc.

Each subsystem should explicitly include its dependencies (e.g.
subsys-obj-y += qemu-timer-common.o or subsys-obj-y +=
$(more-fundamental-subsys)) so that it can be easily used by a target.
 If this is not done then there are two disadvantages:
1. We spray dependency information across the makefiles instead of
keeping them contained with the subsystem that has the dependency
requirement.
2. We duplicate the dependencies across each target in the form of
conditional objects:
x-obj-$(CONFIG_MY_DEPENDENCY) += ...

If QEMU is split up into libraries then having an explicit list of
dependencies for each subsystem will be very useful, whereas the
CONFIG_* approach doesn't collect that information in one place.

So I think explicit subsys-obj-y += qemu-timer-common.o together with
$(sort) during the link stage actually allows for a cleaner build
system.  I prefer that approach.

Stefan