1. 概述
conf的源码位于scripts/kconfig目录下。
2. conf的编译
u-boot配置过程执行make pangu_basic_defconfig V=1，对应于顶层Makefile中的%config目标：
%config: scripts_basic outputmakefile FORCE
$(Q)$(MAKE) $(build)=scripts/kconfig $@在这里展开后相当于：
pangu_basic_defconfig: scripts_basic outputmakefile FORCE
make -f ./scripts/Makefile.build obj=scripts/kconfig pangu_basic_defconfig这个规则的命令会指定参数obj=scripts/kconfig和pangu_basic_defconfig进入scripts/Makefile.build进行编译。
在scripts/Makefile.build中，会根据参数obj=scripts/kconfig，包含scripts/kconfig文件夹下的子Makefile：
# The filename Kbuild has precedence over Makefile
kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
include $(kbuild-file)scripts/kconfig/Makefile中相应的规则为：
%_defconfig: $(obj)/conf
$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)在这里展开为：
pangu_basic_defconfig: scripts/kconfig/conf
scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig由于pangu_basic_defconfig依赖于scripts/kconfig/conf，所以conf将会被编译。
conf依赖于conf.c和zconf.tab.c，后者进一步包含所需要的词法分析文件，整个编译链接过程如下：
make -f ./scripts/Makefile.build obj=scripts/kconfig pangu_basic_defconfig
cc -Wp,-MD,scripts/kconfig/.conf.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -DCURSES_LOC="<ncurses.h>" -DNCURSES_WIDECHAR=1 -DLOCALE -c -o scripts/kconfig/conf.o scripts/kconfig/conf.c
bison -oscripts/kconfig/zconf.tab.c -t -l scripts/kconfig/zconf.y
flex -oscripts/kconfig/zconf.lex.c -L scripts/kconfig/zconf.l
cc -Wp,-MD,scripts/kconfig/.zconf.tab.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -DCURSES_LOC="<ncurses.h>" -DNCURSES_WIDECHAR=1 -DLOCALE -Iscripts/kconfig -c -o scripts/kconfig/zconf.tab.o scripts/kconfig/zconf.tab.c
cc -o scripts/kconfig/conf scripts/kconfig/conf.o scripts/kconfig/zconf.tab.o
scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig（注：执行make pangu_basic_defconfig时，打开V=1选项可以看到整个过程）
除了u-boot配置过程（make pangu_basic_defconfig）外，u-boot编译过程中也有对应的规则编译conf，见顶层Makefile：
# If .config is newer than include/config/auto.conf, someone tinkered
# with it and forgot to run make oldconfig.
# if auto.conf.cmd is missing then we are probably in a cleaned tree so
# we execute the config step to be sure to catch updated Kconfig files
include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
@# If the following part fails, include/config/auto.conf should be
@# deleted so "make silentoldconfig" will be re-run on the next build.
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.autoconf || \
{ rm -f include/config/auto.conf; false; }
@# include/config.h has been updated after "make silentoldconfig".
@# We need to touch include/config/auto.conf so it gets newer
@# than include/config.h.
@# Otherwise, 'make silentoldconfig' would be invoked twice.
$(Q)touch include/config/auto.conf在这个规则中也会根据syncconfig再次检查并更新scripts/kconfig/conf文件。
3. conf调用
在u-boot的配置编译过程中，conf被调用了两次：一次是在配置过程中，一次是在编译过程中。
3.1 在u-boot配置过程中调用
在u-boot的配置过程中，完成conf的编译后，会随即调用命令：
scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig去生成根目录下的.config文件。
3.2 在u-boot编译过程中调用
u-boot配置完成后，执行make命令开始编译时，会检查.config是否比include/config/auto.conf更新，规则如下：
# If .config is newer than include/config/auto.conf, someone tinkered
# with it and forgot to run make oldconfig.
# if auto.conf.cmd is missing then we are probably in a cleaned tree so
# we execute the config step to be sure to catch updated Kconfig files
include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
@# If the following part fails, include/config/auto.conf should be
@# deleted so "make silentoldconfig" will be re-run on the next build.
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.autoconf || \
{ rm -f include/config/auto.conf; false; }
@# include/config.h has been updated after "make silentoldconfig".
@# We need to touch include/config/auto.conf so it gets newer
@# than include/config.h.
@# Otherwise, 'make silentoldconfig' would be invoked twice.
$(Q)touch include/config/auto.conf这个规则的make输出log如下：
make -f ./Makefile syncconfig
make -f ./scripts/Makefile.build obj=scripts/basic
rm -f .tmp_quiet_recordmcount
make -f ./scripts/Makefile.build obj=scripts/kconfig syncconfig
mkdir -p include/config include/generated
scripts/kconfig/conf --syncconfig Kconfig
make -f ./scripts/Makefile.autoconf || \
{ rm -f include/config/auto.conf; false; }
if [ -d arch/arm/mach-stm32mp/include/mach ]; then \
dest=../../mach-stm32mp/include/mach; \
else \
dest=arch-stm32mp; \
fi; \
ln -fsn $dest arch/arm/include/asm/arch
... ...实际执行$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig命令的结果就是检查并更新scripts/kconfig/conf文件，然后调用之：
scripts/kconfig/conf --syncconfig Kconfig。
为了检查这个命令的输出，可以直接在命令行执行命令：
wei@wei-PC:~/stm32mp/uboot/u-boot-st$ make -f ./Makefile syncconfig V=1
make -f ./scripts/Makefile.build obj=scripts/basic
rm -f .tmp_quiet_recordmcount
make -f ./scripts/Makefile.build obj=scripts/kconfig syncconfig
mkdir -p include/config include/generated
scripts/kconfig/conf --syncconfig Kconfig
其实跟命令行上运行make syncconfig是一样的效果。
执行结果就是：
- 在include/config下生成auto.conf和auto.conf.cmd，以及tristate.conf；
- 在include/generated下生成autoconfig.h文件；
3.3 调用简述
简而言之：
- 配置阶段生成.config文件
scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig
- 编译阶段生成auto.conf和autoconf.h
scripts/kconfig/conf --syncconfig Kconfig
4. conf源码分析
conf由conf.o和zconf.tab.o链接而来，其中conf.c生成conf.o，是整个应用的主程序；zconf.tab.c生成zconf.tab.o，完成具体的词法和语法分析任务。
4.1 zconf.tab.c
zconf.tab.c用于读取并分析整个Kconfig系统的文件，较为复杂，也比较枯燥，此处略过。
4.2 conf.c
conf.c是conf主程序的文件，通过分析main函数可以大致了解操作流程：
4.2.1 解析参数部分
while ((opt = getopt_long(ac, av, "s", long_opts, NULL)) != -1) {
if (opt == 's') {
conf_set_message_callback(NULL);
continue;
}
input_mode = (enum input_mode)opt;
switch (opt) {
case syncconfig:
sync_kconfig = 1;
break;
case defconfig:
case savedefconfig:
defconfig_file = optarg;
break;
case randconfig:
{
struct timeval now;
unsigned int seed;
char *seed_env;
/*
* Use microseconds derived seed,
* compensate for systems where it may be zero
*/
gettimeofday(&now, NULL);
seed = (unsigned int)((now.tv_sec + 1) * (now.tv_usec + 1));
seed_env = getenv("KCONFIG_SEED");
if( seed_env && *seed_env ) {
char *endp;
int tmp = (int)strtol(seed_env, &endp, 0);
if (*endp == '\0') {
seed = tmp;
}
}
fprintf( stderr, "KCONFIG_SEED=0x%X\n", seed );
srand(seed);
break;
}
case oldaskconfig:
case oldconfig:
case allnoconfig:
case allyesconfig:
case allmodconfig:
case alldefconfig:
case listnewconfig:
case olddefconfig:
break;
case '?':
conf_usage(progname);
exit(1);
break;
}
}
if (ac == optind) {
fprintf(stderr, _("%s: Kconfig file missing\n"), av[0]);
conf_usage(progname);
exit(1);
}
name = av[optind];
conf_parse(name);
//zconfdump(stdout);
if (sync_kconfig) {
name = conf_get_configname();
if (stat(name, &tmpstat)) {
fprintf(stderr, _("***\n"
"*** Configuration file \"%s\" not found!\n"
"***\n"
"*** Please run some configurator (e.g. \"make oldconfig\" or\n"
"*** \"make menuconfig\" or \"make xconfig\").\n"
"***\n"), name);
exit(1);
}
}
... ...第一次调用：scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig
参数解析后：
- input_mode：defconfig
- defconfig_file：arch/../configs/pangu_basic_defconfig
- name = av[optind]：Kconfig
第二次调用：scripts/kconfig/conf --syncconfig Kconfig
参数解析后：
- input_mode：syncconfig
- name = av[optind]：Kconfig
4.2.2 读取Kconfig系统配置文件
设置好input_mode和name后：
conf_parse(name);
//zconfdump(stdout);
if (sync_kconfig) {
name = conf_get_configname();
if (stat(name, &tmpstat)) {
fprintf(stderr, _("***\n"
"*** Configuration file \"%s\" not found!\n"
"***\n"
"*** Please run some configurator (e.g. \"make oldconfig\" or\n"
"*** \"make menuconfig\" or \"make xconfig\").\n"
"***\n"), name);
exit(1);
}
}- 调用conf_parse(name)从$(srctree)目录下依次查找名为Kconfig的文件，然后将取得的信息存放在链表中；
- 如果syncconfig，即sync_kconfig=1，还要调用conf_get_configname并检查顶层目录下的.config文件是否存在。
4.2.3 读取指定的配置文件
switch (input_mode) {
case defconfig:
if (!defconfig_file)
defconfig_file = conf_get_default_confname();
if (conf_read(defconfig_file)) {
fprintf(stderr,
_("***\n"
"*** Can't find default configuration \"%s\"!\n"
"***\n"),
defconfig_file);
exit(1);
}
break;
case savedefconfig:
case syncconfig:
case ...:
conf_read(NULL);
break;
... ...
default:
break;
}- 如果是defconfig，调用conf_read(defconfig_file)读取指定的配置文件arch/../configs/pangu_basic_defconfig
- 如果是syncconfig，调用conf_read(NULL)读取生成的.config。（conf_read传入的参数为NULL时，在conf_read_simple中会将读取的文件指向.config）
4.2.4 检查更新设置
接下来：
if (sync_kconfig) {
if (conf_get_changed()) {
name = getenv("KCONFIG_NOSILENTUPDATE");
if (name && *name) {
fprintf(stderr,
_("\n*** The configuration requires explicit update.\n\n"));
return 1;
}
}
}
switch (input_mode) {
... ...
case defconfig:
conf_set_all_new_symbols(def_default);
break;
... ...
case oldconfig:
case listnewconfig:
case syncconfig:
/* Update until a loop caused no more changes */
do {
conf_cnt = 0;
check_conf(&rootmenu);
} while (conf_cnt);
break;
case olddefconfig:
default:
break;
}- 如果是syncconfig，检查.config是否被改动的，并检查各项设置的有效性
- 如果是defconfig，设置默认值
4.2.5 更新.config，设置默认值
最后：
if (sync_kconfig) {
/* syncconfig is used during the build so we shall update autoconf.
* All other commands are only used to generate a config.
*/
if (conf_get_changed() && conf_write(NULL)) {
fprintf(stderr, _("\n*** Error during writing of the configuration.\n\n"));
exit(1);
}
if (conf_write_autoconf()) {
fprintf(stderr, _("\n*** Error during update of the configuration.\n\n"));
return 1;
}
} else if (input_mode == savedefconfig) {
if (conf_write_defconfig(defconfig_file)) {
fprintf(stderr, _("n*** Error while saving defconfig to: %s\n\n"),
defconfig_file);
return 1;
}
} else if (input_mode != listnewconfig) {
if (conf_write(NULL)) {
fprintf(stderr, _("\n*** Error during writing of the configuration.\n\n"));
exit(1);
}
}- 如果是syncconfig：
（1）调用conf_get_changed()检查是否更新过，然后调用conf_write(NULL)将更新的项写入到.config文件中
（2）调用conf_write_autoconf()更新以下文件：
include/generated/autoconf.h
include/config/auto.conf.cmd
include/config/tristate.conf
include/config/auto.conf
- 如果是defconfig，进入最后一个(input_mode != listnewconfig)分支，调用conf_write(NULL)，将读取到的所有配置写入.config中。
5. 总结
（1）配置时，执行make pangu_basic_defconfig，会根据规则生成scripts/kconfig/conf工具：
pangu_basic_defconfig: scripts_basic outputmakefile FORCE
make -f ./scripts/Makefile.build obj=scripts/kconfig pangu_basic_defconfig利用生成的scripts/kconfig/conf工具，根据默认配置，在根目录下生成.config文件。
scripts/kconfig/conf --defconfig=arch/../configs/pangu_basic_defconfig Kconfig（2）编译时，执行
scripts/kconfig/conf --syncconfig Kconfig* 检查并分析系统中各个`Kconfig`文件
* 同配置时生成的`.config`比较，更新`.config`文件
* 生成相应的其他文件供下一步编译使用
- `include/generated/autoconf.h`
- `include/config/auto.conf.cmd`
- `include/config/tristate.conf`
- `include/config/auto.conf`