[PATCH v5 05/13] kconfig: Add support for conditional values

Simon Glass
2022-01-22T12:08:47Z

At present if an optional Kconfig value needs to be used it must be
bracketed by #ifdef. For example, with this Kconfig setup:

config WIBBLE
bool "Support wibbles, the world needs more wibbles"

config WIBBLE_ADDR
hex "Address of the wibble"
depends on WIBBLE

then the following code must be used:

#ifdef CONFIG_WIBBLE
static void handle_wibble(void)
{
int val = CONFIG_WIBBLE_ADDR;

...
}
#endif

static void init_machine()
{
...
#ifdef CONFIG_WIBBLE
handle_wibble();
#endif
}

Add a new IF_ENABLED_INT() to help with this. So now it is possible to
write, without #ifdefs:

static void handle_wibble(void)
{
int val = IF_ENABLED_INT(CONFIG_WIBBLE, CONFIG_WIBBLE_ADDR);

...
}

static void init_machine()
{
...
if (IS_ENABLED(CONFIG_WIBBLE))
handle_wibble();
}

The value will be CONFIG_WIBBLE_ADDR if CONFIG_WIBBLE is defined and will
produce a build error if not.. This allows us to reduce the use of #ifdef
in the code, ensuring that the compiler still checks the code even if it
is not ultimately used for a particular build.

Add a CONFIG_IF_ENABLED_INT() version as well.

If an attempt is made to use a value that does not exist (i.e. when the
conditional is not enabled), an error about a non-existing function is
generated, e.g.:

common/bloblist.c:447: undefined reference to `invalid_use_of_IF_ENABLED_INT'

Signed-off-by: Simon Glass <sjg@chromium.org>
---

(no changes since v4)

Changes in v4:
- Update stale mention of zero in commit message
- Update stale comments in the header file
- Define the macros even in assembly context

Changes in v3:
- Add a way to detect use of a non-existent value

include/linux/kconfig.h | 40 +++++++++++++++++++++++++++++++++++++++
scripts/Makefile.autoconf | 2 +-
2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index 52586a7557b..d20da615b96 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -57,6 +57,30 @@
*/
#define CONFIG_VAL(option) config_val(option)

+/*
+ * This uses a similar mechanism to config_enabled() above. If cfg is enabled,
+ * it resolves to the value of opt_cfg, otherwise it resolves to def_val
+ */
+#define config_opt_enabled(cfg, opt_cfg, def_val) _config_opt_enabled(cfg, opt_cfg, def_val)
+#define _config_opt_enabled(cfg_val, opt_value, def_val) \
+ __config_opt_enabled(__ARG_PLACEHOLDER_##cfg_val, opt_value, def_val)
+#define __config_opt_enabled(arg1_or_junk, arg2, def_val) \
+ ___config_opt_enabled(arg1_or_junk arg2, def_val)
+#define ___config_opt_enabled(__ignored, val, ...) val
+
+#ifndef __ASSEMBLY__
+/*
+ * Detect usage of a the value when the conditional is not enabled. When used
+ * in assembly context, this likely produces a assembly error, or hopefully at
+ * least something recognisable.
+ */
+long invalid_use_of_IF_ENABLED_INT(void);
+#endif
+
+/* Evaluates to int_option if option is defined, otherwise a build error */
+#define IF_ENABLED_INT(option, int_option) \
+ config_opt_enabled(option, int_option, invalid_use_of_IF_ENABLED_INT())
+
/*
* Count number of arguments to a variadic macro. Currently only need
* it for 1, 2 or 3 arguments.
@@ -111,5 +135,21 @@
#define CONFIG_IS_ENABLED(option, ...) \
__concat(__CONFIG_IS_ENABLED_, __count_args(option, ##__VA_ARGS__)) (option, ##__VA_ARGS__)

+#ifndef __ASSEMBLY__
+/*
+ * Detect usage of a the value when the conditional is not enabled. When used
+ * in assembly context, this likely produces a assembly error, or hopefully at
+ * least something recognisable.
+ */
+long invalid_use_of_CONFIG_IF_ENABLED_INT(void);
+#endif
+
+/*
+ * Evaluates to SPL_/TPL_int_option if SPL_/TPL_/option is not defined,
+ * otherwise build error
+ */
+#define CONFIG_IF_ENABLED_INT(option, int_option) \
+ CONFIG_IS_ENABLED(option, (CONFIG_VAL(int_option)), \
+ (invalid_use_of_CONFIG_IF_ENABLED_INT()))

#endif /* __LINUX_KCONFIG_H */
diff --git a/scripts/Makefile.autoconf b/scripts/Makefile.autoconf
index 5ed9abc8e14..0b3ffa08bfa 100644
--- a/scripts/Makefile.autoconf
+++ b/scripts/Makefile.autoconf
@@ -68,7 +68,7 @@ quiet_cmd_u_boot_cfg = CFG $@
cmd_u_boot_cfg = \
$(CPP) $(c_flags) $2 -DDO_DEPS_ONLY -dM $(srctree)/include/common.h > $@.tmp && { \
grep 'define CONFIG_' $@.tmp | \
- sed '/define CONFIG_IS_ENABLED(/d;/define CONFIG_VAL(/d;' > $@; \
+ sed '/define CONFIG_IS_ENABLED(/d;/define CONFIG_IF_ENABLED_INT(/d;/define CONFIG_VAL(/d;' > $@; \
rm $@.tmp; \
} || { \
rm $@.tmp; false; \
--
2.35.0.rc0.227.g00780c9af4-goog