Subject: Re: [RFC PATCH v2 2/3] kbuild: Add objtool integration for PowerPC feature fixups

From: Nicolas Schier <[email-masked]>
Date: Sat, 4 Oct 2025 21:43:23 +0200

On Mon, Sep 29, 2025 at 01:34:55PM +0530, Sathvika Vasireddy wrote:
> Add build system support for PowerPC feature fixup processing:
> 
> - Add HAVE_OBJTOOL_FTR_FIXUP config option for architectures that support
>   build-time feature fixup processing
> - Integrate objtool feature fixup processing into vmlinux build
> 
> Suggested-by: Masahiro Yamada <[email-masked]>
> Signed-off-by: Sathvika Vasireddy <[email-masked]>
> ---
>  Makefile                 |  7 +++++++
>  arch/Kconfig             |  3 +++
>  scripts/Makefile.lib     |  5 +++--
>  scripts/Makefile.vmlinux | 13 ++++++++++++-
>  4 files changed, 25 insertions(+), 3 deletions(-)
> 
...
> diff --git a/arch/Kconfig b/arch/Kconfig
> index d1b4ffd6e085..d870aab17cba 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1334,6 +1334,9 @@ config HAVE_UACCESS_VALIDATION
>  	bool
>  	select OBJTOOL
>  
> +config HAVE_OBJTOOL_FTR_FIXUP

For me, FTR is not that natural to parse.  Is there a reason for using
FTR instead of FEATURE?

...
> diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
> index b64862dc6f08..94cc2bba929a 100644
> --- a/scripts/Makefile.vmlinux
> +++ b/scripts/Makefile.vmlinux
> @@ -84,7 +84,8 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
>  # Final link of vmlinux with optional arch pass after final link
>  cmd_link_vmlinux =							\
>  	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
> -	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
> +	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)	\
> +	$(cmd_objtool_vmlinux)
>  
>  targets += $(vmlinux-final)
>  $(vmlinux-final): scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
> @@ -131,3 +132,13 @@ existing-targets := $(wildcard $(sort $(targets)))
>  -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
>  
>  .PHONY: $(PHONY)
> +
> +# objtool for vmlinux
> +# ----------------------------------
> +#
> +#  For feature fixup, objtool does not run on individual
> +#  translation units. Run this on vmlinux instead.
> +
> +ifdef CONFIG_HAVE_OBJTOOL_FTR_FIXUP
> +cmd_objtool_vmlinux = ; $(objtool) --ftr-fixup --link $@

This cmd_* definition is broken as $(call cmd,objtool_vmlinux) would be
evaluated to '... ; ; ...' (shell syntax error).

What about putting the objtool call right into cmd_link_vmlinux?

cmd_link_vmlinux =							\
	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true);   \
	$(if $(CONFIG_HAVE_OBJTOOL_FTR_FIXUP), $(objtool) --ftr-fixup --link $@, true)

Kind regards,
Nicolas