linux-kernel - Re: [PATCH 2/2] kbuild: add 'private' to target-specific variables

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Date: Tue, 7 May 2024 23:25:05 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Nicolas Schier <nicolas@...sle.eu>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH 2/2] kbuild: add 'private' to target-specific variables

On Tue, May 7, 2024 at 8:16 PM Nicolas Schier <nicolas@...sle.eu> wrote:
>
> On Sun, Apr 28, 2024 at 12:32:53AM +0900, Masahiro Yamada wrote:
> > Currently, Kbuild produces inconsistent results in some cases.
> >
> > You can do an interesting experiment using the --shuffle option, which
> > is supported by GNU Make 4.4 or later.
> >
> > Set CONFIG_KVM_INTEL=y and CONFIG_KVM_AMD=m (or vice versa), and repeat
> > incremental builds w/wo --shuffle=reverse.
> >
> >   $ make
> >     [ snip ]
> >     CC      arch/x86/kvm/kvm-asm-offsets.s
> >
> >   $ make --shuffle=reverse
> >     [ snip ]
> >     CC [M]  arch/x86/kvm/kvm-asm-offsets.s
> >
> >   $ make
> >     [ snip ]
> >     CC      arch/x86/kvm/kvm-asm-offsets.s
> >
> > arch/x86/kvm/kvm-asm-offsets.s is rebuilt every time w/wo the [M] marker.
> >
> > arch/x86/kvm/kvm-asm-offsets.s is built as built-in when it is built as
> > a prerequisite of arch/x86/kvm/kvm-intel.o, which is built-in.
> >
> > arch/x86/kvm/kvm-asm-offsets.s is built as modular when it is built as
> > a prerequisite of arch/x86/kvm/kvm-amd.o, which is a module.
> >
> > Another odd example is single target builds.
> >
> > When CONFIG_LKDTM=m, drivers/misc/lkdtm/rodata.o can be built as
> > built-in or modular, depending on how it is built.
> >
> >   $ make drivers/misc/lkdtm/lkdtm.o
> >     [ snip ]
> >     CC [M]  drivers/misc/lkdtm/rodata.o
> >
> >   $ make drivers/misc/lkdtm/rodata.o
> >     [ snip ]
> >     CC      drivers/misc/lkdtm/rodata.o
> >
> > drivers/misc/lkdtm/rodata.o is built as modular when it is built as a
> > prerequisite of another, but built as built-in when it is a final
> > target.
> >
> > The same thing happens to drivers/memory/emif-asm-offsets.s when
> > CONFIG_TI_EMIF_SRAM=m.
> >
> >   $ make drivers/memory/ti-emif-sram.o
> >     [ snip ]
> >     CC [M]  drivers/memory/emif-asm-offsets.s
> >
> >   $ make drivers/memory/emif-asm-offsets.s
> >     [ snip ]
> >     CC      drivers/memory/emif-asm-offsets.s
> >
> > This is because the part-of-module=y flag defined for the modules is
> > inherited by its prerequisites.
> >
> > Target-specific variables are likely intended only for local use.
> > This commit adds 'private' to them.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
>
> uh, thanks for fixing this!  (And for the bug documentation, as always!)
>
> I have just one question below.
>
> >
> >  Makefile               | 8 ++++----
> >  scripts/Makefile.build | 6 +++---
> >  2 files changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 62557fabfee5..25dcc7ead330 100644
> > --- a/Makefile
> > +++ b/Makefile
> [...]
> > @@ -1500,7 +1500,7 @@ MRPROPER_FILES += include/config include/generated          \
> >
> >  # clean - Delete most, but leave enough to build external modules
> >  #
> > -clean: rm-files := $(CLEAN_FILES)
> > +clean: private rm-files := $(CLEAN_FILES)
>
> Did you leave 'clean: rm-files := $(KBUILD_EXTMOD)/...' for oot kmods
> the way it is (w/o 'private') by intention?


No. I missed to update this line.

I will fix it up for consistency. Thanks.





>
> Even though I cannot think of a possible problem without the 'private',
> I think it makes sense to change the line as well.
>
> W/ or w/o the 'clean'-update for oot kmods:
>
> Reviewed-by: Nicolas Schier <n.schier@....de>
>
> Kind regards,
> Nicolas



-- 
Best Regards
Masahiro Yamada