[RFC PATCH] kconfig: introduce KCONFIG_* symbols for .c files

Sam Ravnborg
2008-05-24T19:25:16Z

We have many places in the kernel that looks like
the following:

#ifdef CONFIG_FOO
...
#endif

Which has the disadvantage that the code denoted '...'
are not even built if CONFIG_FOO is not selected in
the current configuration.

We know that gcc do simple code-elimination for
conditionals which is always true/false and
thus the above code could be turned into:

if (CONFIG_FOO)
...

One line smaller and we follow the normal flow in the program.
The code is always build but we do not waste space as gcc will
do proper code-elimination for us.

Today this is not possible because kconfig will only
define CONFIG_FOO if selected and FOO is not a module.

The following patch implement a new set of defines in
the KCONFIG_* namespace.

For a tristate symbol the following are defined:

FOO not selected:
#define KCONFIG_FOO 0
#define KCONFIG_FOO_MODULE 0

FOO is built-in ('y')
#define KCONFIG_FOO 1
#define KCONFIG_FOO_MODULE 0

FOO is a module ('m'):
#define KCONFIG_FOO 1
#define KCONFIG_FOO_MODULE 1

In other words KCONFIG_FOO will say if the
symbol is selected and KCONFIG_FOO_MODULE
will say if it is a module.

With the above included we can now do:

if (KCONFIG_FOO)
...

This is not a replacement for the CONFIG_*
defines but a pleasant supplement.
Using KCONFIG_FOO will also give us a nice
error message the day that FOO is no longer part
of the configuration.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
---
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index ee5fe94..011a5ec 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -666,6 +666,31 @@ out:
return res;
}

+static void write_tristate(FILE *m, FILE *h, struct symbol *sym)
+{
+ switch (sym_get_tristate_value(sym)) {
+ case mod:
+ fprintf(m, "CONFIG_%s=m\n", sym->name);
+ fprintf(h, "#define CONFIG_%s_MODULE 1\n", sym->name);
+ fprintf(h, "#define KCONFIG_%s 1\n", sym->name);
+ if (sym->type == S_TRISTATE)
+ fprintf(h, "#define KCONFIG_%s_MODULE 1\n", sym->name);
+ break;
+ case yes:
+ fprintf(m, "CONFIG_%s=y\n", sym->name);
+ fprintf(h, "#define CONFIG_%s 1\n", sym->name);
+ fprintf(h, "#define KCONFIG_%s 1\n", sym->name);
+ if (sym->type == S_TRISTATE)
+ fprintf(h, "#define KCONFIG_%s_MODULE 0\n", sym->name);
+ break;
+ case no:
+ fprintf(h, "#define KCONFIG_%s 0\n", sym->name);
+ if (sym->type == S_TRISTATE)
+ fprintf(h, "#define KCONFIG_%s_MODULE 0\n", sym->name);
+ break;
+ }
+}
+
int conf_write_autoconf(void)
{
struct symbol *sym;
@@ -716,18 +741,7 @@ int conf_write_autoconf(void)
switch (sym->type) {
case S_BOOLEAN:
case S_TRISTATE:
- switch (sym_get_tristate_value(sym)) {
- case no:
- break;
- case mod:
- fprintf(out, "CONFIG_%s=m\n", sym->name);
- fprintf(out_h, "#define CONFIG_%s_MODULE 1\n", sym->name);
- break;
- case yes:
- fprintf(out, "CONFIG_%s=y\n", sym->name);
- fprintf(out_h, "#define CONFIG_%s 1\n", sym->name);
- break;
- }
+ write_tristate(out, out_h, sym);
break;
case S_STRING:
str = sym_get_string_value(sym);