openwrt, there are 2 way to compile .ko

one way is package build, anothor is single build.

Below is commnd for single build, for compiling rtl8812au, an advance example

make  -C "/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/linux-5.4.154" \
KCFLAGS="-fmacro-prefix-map=/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl=target-mipsel_24kc_musl" HOSTCFLAGS="-O2 \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/host/include \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/hostpkg/include \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/target-mipsel_24kc_musl/host/include \
-Wall -Wmissing-prototypes -Wstrict-prototypes" \
CROSS_COMPILE="mipsel-openwrt-linux-musl-" \
ARCH="mips" \
KBUILD_HAVE_NLS=no \
KBUILD_BUILD_USER="" \
KBUILD_BUILD_HOST="" \
KBUILD_BUILD_TIMESTAMP="Sun Oct 24 09:01:35 2021" \
KBUILD_BUILD_VERSION="0" HOST_LOADLIBES="-L/home/ai7688/0310/openwrt-b4d7885/staging_dir/host/lib" \
KBUILD_HOSTLDLIBS="-L/home/ai7688/0310/openwrt-b4d7885/staging_dir/host/lib" \
CONFIG_SHELL="bash" V=  cmd_syscalls= \
KBUILD_EXTRA_SYMBOLS="\
/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/symvers/rtl8812au-ct.symvers \
/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/symvers/rtl8192eu.symvers \
/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/symvers/gpio-button-hotplug.symvers \
/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/symvers/mac80211.symvers \
/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/symvers/mt76.symvers" \
KERNELRELEASE=5.4.154 \
M="/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/rtl8812au-ct" \
NOSTDINC_FLAGS="\
-nostdinc  \
-isystem /home/ai7688/0310/openwrt-b4d7885/staging_dir/toolchain-mipsel_24kc_gcc-8.4.0_musl/bin/../lib/gcc/mipsel-openwrt-linux-musl/8.4.0/include \
-I/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/rtl8812au-ct \
-I/home/ai7688/0310/openwrt-b4d7885/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/rtl8812au-ct/include \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/target-mipsel_24kc_musl/usr/include/mac80211-backport \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/target-mipsel_24kc_musl/usr/include/mac80211-backport/uapi \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/target-mipsel_24kc_musl/usr/include/mac80211 \
-I/home/ai7688/0310/openwrt-b4d7885/staging_dir/target-mipsel_24kc_musl/usr/include/mac80211/uapi \
-include backport/backport.h \
-DCONFIG_IOCTL_CFG80211 \
-DRTW_USE_CFG80211_STA_EVENT \
-DCONFIG_CONCURRENT_MODE \
-DBUILD_OPENWRT" modules