Messages in this thread Patch in this message | | | Date | Sat, 24 May 2008 21:25:40 +0200 | From | Sam Ravnborg <> | Subject | [RFC PATCH] kconfig: introduce KCONFIG_* symbols for .c files |
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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);
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