linux-kernel - Re: [PATCH 2/3] objtool: move libelf check out of top Makefile

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Date:   Tue, 16 Oct 2018 09:25:40 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Borislav Petkov <bp@...e.de>, Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] objtool: move libelf check out of top Makefile

On Tue, Oct 16, 2018 at 06:10:52PM +0900, Masahiro Yamada wrote:
> Another behavioral change is, missing libelf for CONFIG_STACK_VALIDATION
> was previously a warning, but now a error.

This behavioral change should be fine.  It was already an error for
UNWINDER_ORC, so this would only upgrade a warning to an error for
people using STACK_VALIDATION without ORC, which should be a small
number of people by this point.

> diff --git a/scripts/Makefile.toolcheck b/scripts/Makefile.toolcheck
> index f3c165d..bc26fc0 100644
> --- a/scripts/Makefile.toolcheck
> +++ b/scripts/Makefile.toolcheck
> @@ -12,6 +12,11 @@ include include/config/auto.conf
>  __toolcheck:
>  	@:
>  
> +chk_stack_validation = echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -
> +msg_stack_validation = "libelf is necessary for building the objtool." \
> +		       "Please install libelf-dev, libelf-devel or elfutils-libelf-devel."
> +toolcheck-$(CONFIG_STACK_VALIDATION) += stack_validation
> +
>  PHONY += $(toolcheck-y)
>  __toolcheck: $(toolcheck-y)

This is a nice improvement.

It would probably be a good idea to clarify to the user which config
option(s) are the cause for the error, by putting
"CONFIG_STACK_VALIDATION" in the error string, for example.

Though, for this particular case, it would be clearer to have a
different error, based on which option is enabled, like we had before.

Like:


ifdef CONFIG_UNWINDER_ORC

chk_unwinder_orc = echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -
msg_unwinder_orc = "Cannot build objtool to generate ORC metadata for CONFIG_UNWINDER_ORC=y.  " \
		       "Please install libelf-dev, libelf-devel or elfutils-libelf-devel."
toolcheck-$(CONFIG_UNWINDER_ORC) += unwinder_orc

else

chk_stack_validation = echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -
msg_stack_validation = "Cannot build objtool for CONFIG_STACK_VALIDATION=y.  " \
		       "Please install libelf-dev, libelf-devel or elfutils-libelf-devel."
toolcheck-$(CONFIG_STACK_VALIDATION) += stack_validation

endif


What do you think?

-- 
Josh