linux-kernel - Re: [PATCH 2/2] kconfig: make 'imply' obey the direct dependency

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Date:   Mon, 2 Mar 2020 10:33:19 -0500 (EST)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Masahiro Yamada <masahiroy@...nel.org>
cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ulf Magnusson <ulfalizer@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] kconfig: make 'imply' obey the direct dependency

On Mon, 2 Mar 2020, Masahiro Yamada wrote:

> The 'imply' statement may create unmet direct dependency when the
> implied symbol depends on m.
> 
> [Test Code]
> 
>   config FOO
>           tristate "foo"
>           imply BAZ
> 
>   config BAZ
>           tristate "baz"
>           depends on BAR
> 
>   config BAR
>           def_tristate m
> 
>   config MODULES
>           def_bool y
>           option modules
> 
> If you set FOO=y, BAZ is also promoted to y, which results in the
> following .config file:
> 
>   CONFIG_FOO=y
>   CONFIG_BAZ=y
>   CONFIG_BAR=m
>   CONFIG_MODULES=y
> 
> This does not meet the dependency 'BAZ depends on BAR'.
> 
> Unlike 'select', what is worse, Kconfig never shows the
> 'WARNING: unmet direct dependencies detected for ...' for this case.
> 
> Because 'imply' is considered to be weaker than 'depends on', Kconfig
> should take the direct dependency into account.
> 
> For clarification, describe this case in kconfig-language.rst too.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Acked-by: Nicolas Pitre <nico@...xnic.net>

> ---
> 
>  Documentation/kbuild/kconfig-language.rst | 7 +++++--
>  scripts/kconfig/symbol.c                  | 4 +++-
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index d4d988aea679..68719e78ff85 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -159,11 +159,11 @@ applicable everywhere (see syntax).
>    Given the following example::
>  
>      config FOO
> -	tristate
> +	tristate "foo"
>  	imply BAZ
>  
>      config BAZ
> -	tristate
> +	tristate "baz"
>  	depends on BAR
>  
>    The following values are possible:
> @@ -174,6 +174,9 @@ applicable everywhere (see syntax).
>  	n		y		n		N/m/y
>  	m		y		m		M/y/n
>  	y		y		y		Y/m/n
> +	n		m		n		N/m
> +	m		m		m		M/n
> +	y		m		n		M/n
>  	y		n		*		N
>  	===		===		=============	==============
>  
> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
> index b101ef3c377a..3dc81397d003 100644
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -221,7 +221,7 @@ static void sym_calc_visibility(struct symbol *sym)
>  		sym_set_changed(sym);
>  	}
>  	tri = no;
> -	if (sym->implied.expr && sym->dir_dep.tri != no)
> +	if (sym->implied.expr)
>  		tri = expr_calc_value(sym->implied.expr);
>  	if (tri == mod && sym_get_type(sym) == S_BOOLEAN)
>  		tri = yes;
> @@ -394,6 +394,8 @@ void sym_calc_value(struct symbol *sym)
>  				if (sym->implied.tri != no) {
>  					sym->flags |= SYMBOL_WRITE;
>  					newval.tri = EXPR_OR(newval.tri, sym->implied.tri);
> +					newval.tri = EXPR_AND(newval.tri,
> +							      sym->dir_dep.tri);
>  				}
>  			}
>  		calc_newval:
> -- 
> 2.17.1
> 
>