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

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Date:   Mon,  2 Mar 2020 15:23:40 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Nicolas Pitre <nico@...xnic.net>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-doc@...r.kernel.org
Subject: [PATCH 2/2] kconfig: make 'imply' obey the direct dependency

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>
---

 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