Subject: Re: [PATCH 1/2] kbuild: Hoist '--orphan-handling' into Kconfig

From: Michael Ellerman <[email-masked]>
Date: Tue, 17 Nov 2020 22:03:29 +1100

Nathan Chancellor <[email-masked]> writes:
> Currently, '--orphan-handling=warn' is spread out across four different
> architectures in their respective Makefiles, which makes it a little
> unruly to deal with in case it needs to be disabled for a specific
> linker version (in this case, ld.lld 10.0.1).
>
> To make it easier to control this, hoist this warning into Kconfig and
> the main Makefile so that disabling it is simpler, as the warning will
> only be enabled in a couple places (main Makefile and a couple of
> compressed boot folders that blow away LDFLAGS_vmlinx) and making it
> conditional is easier due to Kconfig syntax. One small additional
> benefit of this is saving a call to ld-option on incremental builds
> because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.
>
> To keep the list of supported architectures the same, introduce
> CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
> gain this automatically after all of the sections are specified and size
> asserted. A special thanks to Kees Cook for the help text on this
> config.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Signed-off-by: Nathan Chancellor <[email-masked]>
> ---
>  Makefile                          | 6 ++++++
>  arch/Kconfig                      | 9 +++++++++
>  arch/arm/Kconfig                  | 1 +
>  arch/arm/Makefile                 | 4 ----
>  arch/arm/boot/compressed/Makefile | 4 +++-
>  arch/arm64/Kconfig                | 1 +
>  arch/arm64/Makefile               | 4 ----
>  arch/powerpc/Kconfig              | 1 +
>  arch/powerpc/Makefile             | 1 -

Acked-by: Michael Ellerman <[email-masked]> (powerpc)

>  arch/x86/Kconfig                  | 1 +
>  arch/x86/Makefile                 | 3 ---
>  arch/x86/boot/compressed/Makefile | 4 +++-
>  init/Kconfig                      | 3 +++
>  13 files changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 008aba5f1a20..c443afd61886 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -984,6 +984,12 @@ ifeq ($(CONFIG_RELR),y)
>  LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
>  endif
>  
> +# We never want expected sections to be placed heuristically by the
> +# linker. All sections should be explicitly named in the linker script.
> +ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
> +LDFLAGS_vmlinux += --orphan-handling=warn
> +endif

This is a nit, but you can use ifdef with bool CONFIG symbols in
Makefiles, which reads a bit nicer, eg:

ifdef CONFIG_LD_ORPHAN_WARN
LDFLAGS_vmlinux += --orphan-handling=warn
endif

cheers