[PATCH RESEND] arm64: fix vdso-offsets.h dependency

[Catalin Marinas]

On Wed, Jul 06, 2016 at 06:57:39PM +0100, Catalin Marinas wrote:
> On Thu, May 12, 2016 at 05:39:15PM +0100, Kevin Brodsky wrote:
> > +# We need to generate vdso-offsets.h before compiling certain files in kernel/.
> > +# In order to do that, we should use the archprepare target, but we can't since
> > +# asm-offsets.h is included in some files used to generate vdso-offsets.h, and
> > +# asm-offsets.h is built in prepare0, for which archprepare is a dependency.
> > +# Therefore we need to generate the header after prepare0 has been made, hence
> > +# this hack.
> > +prepare: vdso_prepare
> > +vdso_prepare: prepare0
> > +	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
> 
> This indeed looks dodgy. I'm not sure about the makefile rules but would
> the above override the "prepare" target in the top Makefile?
> 
> I think a dependency problem we have is that arch/arm64/kernel/signal.o
> depends on include/generated/vdso-offsets.h. However, we don't have any
> target for the latter, only for
> $(objtree)arch/arm64/kernel/vdso/vdso-offsets.h which no-one is
> including. Because of this, we have a fake dependency in
> arch/arm64/kernel/Makefile.
> 
> -----------8<-------------------------
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 7700c0c23962..9bdacbf59091 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -55,5 +55,4 @@ head-y					:= head.o
>  extra-y					+= $(head-y) vmlinux.lds
>  
>  # vDSO - this must be built first to generate the symbol offsets
> -$(call objectify,$(arm64-obj-y)): $(obj)/vdso/vdso-offsets.h
> -$(obj)/vdso/vdso-offsets.h: $(obj)/vdso
> +$(objtree)/include/generated/vdso-offsets.h: $(obj)/vdso

This didn't work either. Basically, when building
arch/arm64/kernel/signal.o for example, it doesn't figure out that
vdso-offsets.h has additional dependencies like the vdso.so.dbg so that
it builds the vdso object first. I'll look for a little longer, maybe I
find a better workaround.

-- 
Catalin