linux-kernel - Re: [PATCH] kbuild: fix false positive warning/error about missing libelf

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Date:   Tue, 18 Dec 2018 09:34:08 -0500
From:   Qian Cai <cai@....pw>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kbuild@...r.kernel.org
Cc:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: fix false positive warning/error about missing
 libelf

On Tue, 2018-12-18 at 14:25 +0900, Masahiro Yamada wrote:
> For the same reason as commit 25896d073d8a ("x86/build: Fix compiler
> support check for CONFIG_RETPOLINE"), you cannot put this $(error ...)
> into the parse stage of the top Makefile.
> 
> Perhaps I'd propose a more sophisticated solution later, but this is
> the best I can do for now.
> 
> Link: https://lkml.org/lkml/2017/12/25/211
> Reported-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> Reported-by: Bernd Edlinger <bernd.edlinger@...mail.de>
> Reported-by: Qian Cai <cai@....pw>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 

Tested-by: Qian Cai <cai@....pw>

>  Makefile | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 56d5270..d45856f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -962,11 +962,6 @@ ifdef CONFIG_STACK_VALIDATION
>    ifeq ($(has_libelf),1)
>      objtool_target := tools/objtool FORCE
>    else
> -    ifdef CONFIG_UNWINDER_ORC
> -      $(error "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please
> install libelf-dev, libelf-devel or elfutils-libelf-devel")
> -    else
> -      $(warning "Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-
> dev, libelf-devel or elfutils-libelf-devel")
> -    endif
>      SKIP_STACK_VALIDATION := 1
>      export SKIP_STACK_VALIDATION
>    endif
> @@ -1125,6 +1120,14 @@ uapi-asm-generic:
>  
>  PHONY += prepare-objtool
>  prepare-objtool: $(objtool_target)
> +ifeq ($(SKIP_STACK_VALIDATION),1)
> +ifdef CONFIG_UNWINDER_ORC
> +	@echo "error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y,
> please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
> +	@false
> +else
> +	@echo "warning: Cannot use CONFIG_STACK_VALIDATION=y, please install
> libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
> +endif
> +endif
>  
>  # Generate some files
>  # ---------------------------------------------------------------------------