[RFC PATCH v2 4/5] kbuild: Add generic hook for architectures to use before the final vmlinux link

[Naveen N Rao]

On Mon, Jun 10, 2024 at 06:14:51PM GMT, Masahiro Yamada wrote:
> On Mon, Jun 10, 2024 at 5:39 PM Naveen N Rao <naveen at kernel.org> wrote:
> >
> > On powerpc, we would like to be able to make a pass on vmlinux.o and
> > generate a new object file to be linked into vmlinux. Add a generic pass
> > in link-vmlinux.sh that architectures can use for this purpose.
> > Architectures need to select CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX and must
> > provide arch/<arch>/tools/vmlinux_o.sh, which will be invoked prior to
> > the final vmlinux link step.
> >
> > Signed-off-by: Naveen N Rao <naveen at kernel.org>
> > ---
> >  arch/Kconfig            |  3 +++
> >  scripts/link-vmlinux.sh | 18 +++++++++++++++---
> >  2 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 975dd22a2dbd..649f0903e7ef 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -1643,4 +1643,7 @@ config CC_HAS_SANE_FUNCTION_ALIGNMENT
> >  config ARCH_NEED_CMPXCHG_1_EMU
> >         bool
> >
> > +config ARCH_WANTS_PRE_LINK_VMLINUX
> > +       def_bool n
> > +
> >  endmenu
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index 46ce5d04dbeb..07f70e105d82 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
...
> >
> > +arch_vmlinux_o=""
> > +if is_enabled CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX; then
> > +       arch_vmlinux_o=.arch.vmlinux.o
> > +       info "ARCH" ${arch_vmlinux_o}
> > +       if ! ${srctree}/arch/${SRCARCH}/tools/vmlinux_o.sh ${arch_vmlinux_o} ; then
> > +               echo >&2 "Failed to generate ${arch_vmlinux_o}"
> > +               echo >&2 "Try to disable CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX"
> > +               exit 1
> > +       fi
> > +fi
> 
> 
> 
> This is wrong because scripts/link-vmlinux.sh is not triggered
> even when source files under arch/powerpc/tools/ are changed.
> 
> Presumably, scripts/Makefile.vmlinux will be the right place.

Ah, yes. Something like this?

diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 49946cb96844..77d90b6ac53e 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -22,6 +22,10 @@ targets += .vmlinux.export.o
 vmlinux: .vmlinux.export.o
 endif

+ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
+vmlinux: $(srctree)/arch/$(SRCARCH)/tools/vmlinux_o.sh
+endif
+
 ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)

 # Final link of vmlinux with optional arch pass after final link


Thanks,
Naveen