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理解 openwrt/scripts/kconfig.pl ，了解.config 的生成
一般的编译内核
.config 是由 make xxx_defconfig 生成的
在OpenWrt 中则更复杂些
涉及的文件有
需要理清上述文件的关系，摘取编译时的输出如下：
/openwrt/scripts/kconfig.pl + + /openwrt/target/linux/generic/config-4.14 /openwrt/target/linux/sunxi/config-4.14 /openwrt/target/linux/sunxi/cortexa7/config-default > /openwrt/build_dir/target-arm_cortex-a7+neon-vfpv4_glibc_eabi/linux-sunxi_cortexa7/linux-4.14.63/.config.target
awk '/^(#[[:space:]]+)?CONFIG_KERNEL/{sub("CONFIG_KERNEL_","CONFIG_");print}' /openwrt/.config >> /openwrt/build_dir/target-arm_cortex-a7+neon-vfpv4_glibc_eabi/linux-sunxi_cortexa7/linux-4.14.63/.config.target
为理解 openwrt/scripts/kconfig.pl 的用途，创建 A.config B.config C.config
$ cat A.config
CONFIG_A=y
$ cat B.config
CONFIG_B=y
$ cat C.config
CONFIG_C=y
$ /openwrt/scripts/kconfig.pl + + A.config B.config C.config
CONFIG_A=y
CONFIG_B=y
CONFIG_C=y
可见 /openwrt/scripts/kconfig.pl + + 作用是将三个文件的配置拼成一个。
那当三个文件存在冲突时，输出会怎么样呢。
我们修改 C.config
$ vi C.config
CONFIG_C=y
CONFIG_B=m
输出如下：
$ /openwrt/scripts/kconfig.pl + + A.config B.config C.config
CONFIG_A=y
CONFIG_B=m
CONFIG_C=y
可见C.config 会覆盖 B.config
再验证 B 是否覆盖 A
$ vi B.config
CONFIG_B=y
CONFIG_A=m
$ /openwrt/scripts/kconfig.pl + + A.config B.config C.config
CONFIG_A=m
CONFIG_B=y
CONFIG_C=y
确实是 B > A
总结：当存在冲突时，优先顺序是 C > B > A 。
$ cat A.config
CONFIG_A=y
CONFIG_B=y
CONFIG_ALL=y
$ cat B.config
CONFIG_B=y
CONFIG_A=m
减法 -
$ /openwrt/scripts/kconfig.pl - A.config B.config
CONFIG_ALL=y
与 &
$ /openwrt/scripts/kconfig.pl \& A.config B.config
CONFIG_B=y
diff >
$ /openwrt/scripts/kconfig.pl \> A.config B.config
CONFIG_A=m
m+
$ /openwrt/scripts/kconfig.pl m+ A.config B.config
CONFIG_A=y
CONFIG_ALL=y
CONFIG_B=y
#!/usr/bin/env perl
#
# Copyright (C) 2006 Felix Fietkau <nbd@nbd.name>
#
# This is free software, licensed under the GNU General Public License v2.
# See /LICENSE for more information.
#
use warnings;
use strict;
my @arg;
my $PREFIX = "CONFIG_";
sub set_config($$$$) {
my $config = shift;
my $idx = shift;
my $newval = shift;
my $mod_plus = shift;
if (!defined($config->{$idx}) or !$mod_plus or
$config->{$idx} eq '#undef' or $newval eq 'y') {
$config->{$idx} = $newval;
}
}
sub load_config($$) {
my $file = shift;
my $mod_plus = shift;
my %config;
open FILE, "$file" or die "can't open file '$file'";
while (<FILE>) {
chomp;
/^$PREFIX(.+?)=(.+)/ and do {
set_config(\%config, $1, $2, $mod_plus);
next;
};
/^# $PREFIX(.+?) is not set/ and do {
set_config(\%config, $1, "#undef", $mod_plus);
next;
};
/^#/ and next;
/^(.+)$/ and warn "WARNING: can't parse line: $1\n";
}
return \%config;
}
sub config_and($$) {
my $cfg1 = shift;
my $cfg2 = shift;
my %config;
foreach my $config (keys %$cfg1) {
my $val1 = $cfg1->{$config};
my $val2 = $cfg2->{$config};
$val2 and ($val1 eq $val2) and do {
$config{$config} = $val1;
};
}
return \%config;
}
sub config_add($$$) {
my $cfg1 = shift;
my $cfg2 = shift;
my $mod_plus = shift;
my %config;
for ($cfg1, $cfg2) {
my %cfg = %$_;
foreach my $config (keys %cfg) {
if ($mod_plus and $config{$config}) {
next if $config{$config} eq "y";
next if $cfg{$config} eq '#undef';
}
$config{$config} = $cfg{$config};
}
}
return \%config;
}
sub config_diff($$$) {
my $cfg1 = shift;
my $cfg2 = shift;
my $new_only = shift;
my %config;
foreach my $config (keys %$cfg2) {
if (!defined($cfg1->{$config}) or $cfg1->{$config} ne $cfg2->{$config}) {
next if $new_only and !defined($cfg1->{$config}) and $cfg2->{$config} eq '#undef';
$config{$config} = $cfg2->{$config};
}
}
return \%config
}
sub config_sub($$) {
my $cfg1 = shift;
my $cfg2 = shift;
my %config = %{$cfg1};
foreach my $config (keys %$cfg2) {
delete $config{$config};
}
return \%config;
}
sub print_cfgline($$) {
my $name = shift;
my $val = shift;
if ($val eq '#undef' or $val eq 'n') {
print "# $PREFIX$name is not set\n";
} else {
print "$PREFIX$name=$val\n";
}
}
sub dump_config($) {
my $cfg = shift;
die "argument error in dump_config" unless ($cfg);
my %config = %$cfg;
foreach my $config (sort keys %config) {
print_cfgline($config, $config{$config});
}
}
sub parse_expr {
my $pos = shift;
my $mod_plus = shift;
my $arg = $arg[$$pos++];
die "Parse error" if (!$arg);
if ($arg eq '&') {
my $arg1 = parse_expr($pos);
my $arg2 = parse_expr($pos);
return config_and($arg1, $arg2);
} elsif ($arg =~ /^\+/) {
my $arg1 = parse_expr($pos);
my $arg2 = parse_expr($pos);
return config_add($arg1, $arg2, 0);
} elsif ($arg =~ /^m\+/) {
my $arg1 = parse_expr($pos);
my $arg2 = parse_expr($pos, 1);
