linux-kernel - Re: [PATCH 1/2] kconfig: report recursive dependency involving 'imply'

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Date:   Tue, 14 Aug 2018 12:38:25 +0200
From:   Dirk Gouders <dirk@...ders.net>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Sam Ravnborg <sam@...nborg.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kconfig: report recursive dependency involving 'imply'

Masahiro Yamada <yamada.masahiro@...ionext.com> writes:

> Currently, Kconfig does not report anything about the recursive
> dependency where 'imply' keywords are involved.
>
> [Test Code]
>
>   config A
>           bool "a"
>
>   config B
>           bool "b"
>           imply A
>           depends on A

Hello Masahiro,

obviously, it is hard to find a reason why one wants to use dependencies
like above but I also wonder how e.g. menuconfig handles this case:

First, only "a" is visible, if I then select "a", "b" does not become
visible but when I then reset "a" to "n", "b" becomes visible.  If I then
try to select "b", it becomes invisible...

Perhaps it would be better to just error out instead of giving users the
impression, Kconfig thinks such questionable behavior is OK.

Side note: perhaps, the documentation could be better when it comes to
           recursive dependencies.  The documentation says "select" and
           "imply" can be used to specify lower limits whereas direct
           dependencies specify upper limits for symbol values and with
           this in mind, one might wonder why it is a problem to work
           with both limits in a recursive way.

           Not very unlikely that it is just me who still has to
           understand recursive dependencies or problems with reading
           English text, though.

What definitely seems to get void with your patches is item c) in
"Practical solutions to kconfig recursive issue" in
Documentation/kbuild/kconfig-language:

        c) Consider the use of "imply" instead of "select"

Dirk

> In the code above, Kconfig cannot calculate the symbol values correctly
> due to the circular dependency.  For example, allyesconfig followed by
> syncconfig results in an odd behavior because CONFIG_B becomes visible
> in syncconfig.
>
>   $ make allyesconfig
>   scripts/kconfig/conf  --allyesconfig Kconfig
>   #
>   # configuration written to .config
>   #
>   $ cat .config
>   #
>   # Automatically generated file; DO NOT EDIT.
>   # Main menu
>   #
>   CONFIG_A=y
>   $ make syncconfig
>   scripts/kconfig/conf  --syncconfig Kconfig
>   *
>   * Restart config...
>   *
>   *
>   * Main menu
>   *
>   a (A) [Y/n/?] y
>     b (B) [N/y/?] (NEW)
>
> To report this correctly, sym_check_expr_deps() should recurse to
> not only sym->rev_dep.expr but also sym->implied.expr .
>
> At this moment, sym_check_print_recursive() cannot distinguish
> 'select' and 'imply' since it does not know the precise context
> where the recursive dependency is hit.  This will be solved by
> the next commit.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
>  scripts/kconfig/symbol.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
> index 4ec8b1f..7de7463a 100644
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -1098,7 +1098,7 @@ static void sym_check_print_recursive(struct symbol *last_sym)
>  				sym->name ? sym->name : "<choice>",
>  				next_sym->name ? next_sym->name : "<choice>");
>  		} else {
> -			fprintf(stderr, "%s:%d:\tsymbol %s is selected by %s\n",
> +			fprintf(stderr, "%s:%d:\tsymbol %s is selected or implied by %s\n",
>  				prop->file->name, prop->lineno,
>  				sym->name ? sym->name : "<choice>",
>  				next_sym->name ? next_sym->name : "<choice>");
> @@ -1161,8 +1161,13 @@ static struct symbol *sym_check_sym_deps(struct symbol *sym)
>  	if (sym2)
>  		goto out;
>  
> +	sym2 = sym_check_expr_deps(sym->implied.expr);
> +	if (sym2)
> +		goto out;
> +
>  	for (prop = sym->prop; prop; prop = prop->next) {
> -		if (prop->type == P_CHOICE || prop->type == P_SELECT)
> +		if (prop->type == P_CHOICE || prop->type == P_SELECT ||
> +		    prop->type == P_IMPLY)
>  			continue;
>  		stack.prop = prop;
>  		sym2 = sym_check_expr_deps(prop->visible.expr);