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

Message ID 20160707112325.GB27180@e104818-lin.cambridge.arm.com
State New
Headers show

Commit Message

Catalin Marinas July 7, 2016, 11:23 a.m. UTC 
On Thu, Jul 07, 2016 at 11:26:01AM +0100, Catalin Marinas wrote:
> 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.


If I also add the patch below, it works fine but I'm not sure we can
guarantee that kbuild first dives into subdirectories with a parallel
build:

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diff mbox

Patch

--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -49,11 +49,7 @@  arm64-obj-$(CONFIG_HIBERNATION)		+= hibernate.o hibernate-asm.o
 arm64-obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o	\
 					   cpu-reset.o
 
-obj-y					+= $(arm64-obj-y) vdso/
+obj-y					+= vdso/ $(arm64-obj-y)
 obj-m					+= $(arm64-obj-m)
 head-y					:= head.o
 extra-y					+= $(head-y) vmlinux.lds

-- 
Catalin