path: root/scripts
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authorUlf Magnusson <ulfalizer@gmail.com>2018-02-23 12:49:01 +0100
committerMasahiro Yamada <yamada.masahiro@socionext.com>2018-03-26 02:03:58 +0900
commitf467c5640c29ad258c3cd8186a776c82fc3b8057 (patch)
tree81c7c1ef0d3aa74d1cba9ba9b986a61691250a76 /scripts
parentd9119b5925a03b9a3191fa3e93b4091651d8ad25 (diff)
kconfig: only write '# CONFIG_FOO is not set' for visible symbols
=== Background === - Visible n-valued bool/tristate symbols generate a '# CONFIG_FOO is not set' line in the .config file. The idea is to remember the user selection without having to set a Makefile variable. Having n correspond to the variable being undefined in the Makefiles makes for easy CONFIG_* tests. - Invisible n-valued bool/tristate symbols normally do not generate a '# CONFIG_FOO is not set' line, because user values from .config files have no effect on invisible symbols anyway. Currently, there is one exception to this rule: Any bool/tristate symbol that gets the value n through a 'default' property generates a '# CONFIG_FOO is not set' line, even if the symbol is invisible. Note that this only applies to explicitly given defaults, and not when the symbol implicitly defaults to n (like bool/tristate symbols without 'default' properties do). This is inconsistent, and seems redundant: - As mentioned, the '# CONFIG_FOO is not set' won't affect the symbol once the .config is read back in. - Even if the symbol is invisible at first but becomes visible later, there shouldn't be any harm in recalculating the default value rather than viewing the '# CONFIG_FOO is not set' as a previous user value of n. === Changes === Change sym_calc_value() to only set SYMBOL_WRITE (write to .config) for non-n-valued 'default' properties. Note that SYMBOL_WRITE is always set for visible symbols regardless of whether they have 'default' properties or not, so this change only affects invisible symbols. This reduces the size of the x86 .config on my system by about 1% (due to removed '# CONFIG_FOO is not set' entries). One side effect of (and the main motivation for) this change is making the following two definitions behave exactly the same: config FOO bool config FOO bool default n With this change, neither of these will generate a '# CONFIG_FOO is not set' line (assuming FOO isn't selected/implied). That might make it clearer to people that a bare 'default n' is redundant. This change only affects generated .config files and not autoconf.h: autoconf.h only includes #defines for non-n bool/tristate symbols. === Testing === The following testing was done with the x86 Kconfigs: - .config files generated before and after the change were compared to verify that the only difference is some '# CONFIG_FOO is not set' entries disappearing. A couple of these were inspected manually, and most turned out to be from redundant 'default n/def_bool n' properties. - The generated include/generated/autoconf.h was compared before and after the change and verified to be identical. - As a sanity check, the same modification was done to Kconfiglib. The Kconfiglib test suite was then run to check for any mismatches against the output of the C implementation. Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Diffstat (limited to 'scripts')
1 files changed, 2 insertions, 1 deletions
diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
index 2220bc4b051b..0f7eba7d472a 100644
--- a/scripts/kconfig/symbol.c
+++ b/scripts/kconfig/symbol.c
@@ -403,9 +403,10 @@ void sym_calc_value(struct symbol *sym)
if (!sym_is_choice(sym)) {
prop = sym_get_default_prop(sym);
if (prop) {
- sym->flags |= SYMBOL_WRITE;
newval.tri = EXPR_AND(expr_calc_value(prop->expr),
+ if (newval.tri != no)
+ sym->flags |= SYMBOL_WRITE;
if (sym->implied.tri != no) {
sym->flags |= SYMBOL_WRITE;