【症状】
编译内核模块时，只显示最底部的Error，不显示任何C语言的错误信息。
[oct1158@fed41-bh8f7e0 first]$ make
make -C /home/oct1158/Documents/Code/C/luckfox-pico/sysdrv/source/kernel M=/home/oct1158/Documents/Code/C/driver_test/first modules ARCH=arm CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-
make[2]: *** [scripts/Makefile.build:273: /home/oct1158/Documents/Code/C/driver_test/first/test.o] Error 1
make[1]: *** [Makefile:1935: /home/oct1158/Documents/Code/C/driver_test/first] Error 2
make: *** [Makefile:7: build] Error 2
[oct1158@fed41-bh8f7e0 first]$

【原因】
make命令中含有s字符，导致进入了安静模式。
make -C /home/oct1158/Documents/Code/C/luckfox-pico/sysdrv/source/kernel M=/home/oct1158/Documents/Code/C/driver_test/first modules ARCH=arm CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-
在这句命令中，“driver_test”就含有s字符，所以就会触发安静模式。

$(MAKEFLAGS)变量的值：
rR --no-print-directory -- CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf- ARCH=arm M=/home/oct1158/Documents/Code/C/driver_test/first

$(filter-out --%,$(MAKEFLAGS))表达式的值：
rR CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf- ARCH=arm M=/home/oct1158/Documents/Code/C/driver_test/first
可见这个表达式含有s字符。

【解决办法】
注释掉内核根目录的Makefile文件里面的下面三句话。
ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
  quiet=silent_
endif
禁止进入安静模式。

修改后就有错误信息输出了。
[oct1158@fed41-bh8f7e0 first]$ make
make -C /home/oct1158/Documents/Code/C/luckfox-pico/sysdrv/source/kernel M=/home/oct1158/Documents/Code/C/driver_test/first modules ARCH=arm CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-
  CC [M]  /home/oct1158/Documents/Code/C/driver_test/first/test.o
/home/oct1158/Documents/Code/C/driver_test/first/test.c: In function 'mytestdriver_probe':
/home/oct1158/Documents/Code/C/driver_test/first/test.c:10:9: error: implicit declaration of function 'devm_gpiod_get'; did you mean 'em_pd_get'? [-Werror=implicit-function-declaration]
  gpio = devm_gpiod_get(&pdev->dev, NULL, GPIOD_OUT_HIGH); // led on
         ^~~~~~~~~~~~~~
         em_pd_get
/home/oct1158/Documents/Code/C/driver_test/first/test.c:10:42: error: 'GPIOD_OUT_HIGH' undeclared (first use in this function)
  gpio = devm_gpiod_get(&pdev->dev, NULL, GPIOD_OUT_HIGH); // led on
                                          ^~~~~~~~~~~~~~
/home/oct1158/Documents/Code/C/driver_test/first/test.c:10:42: note: each undeclared identifier is reported only once for each function it appears in
/home/oct1158/Documents/Code/C/driver_test/first/test.c: In function 'mytestdriver_remove':
/home/oct1158/Documents/Code/C/driver_test/first/test.c:28:3: error: implicit declaration of function 'gpiod_set_value'; did you mean 'bitmap_set_value8'? [-Werror=implicit-function-declaration]
   gpiod_set_value(gpio, 0); // led off
   ^~~~~~~~~~~~~~~
   bitmap_set_value8
cc1: all warnings being treated as errors
make[2]: *** [scripts/Makefile.build:273: /home/oct1158/Documents/Code/C/driver_test/first/test.o] Error 1
make[1]: *** [Makefile:1935: /home/oct1158/Documents/Code/C/driver_test/first] Error 2
make: *** [Makefile:7: build] Error 2
[oct1158@fed41-bh8f7e0 first]$

事实上，在编译内核模块时，就算make命令没带CROSS_COMPILE=参数，M=参数肯定是必须带的。我们很难保证M参数里面没有s这个字符。

修改C语言的错误后：
[oct1158@fed41-bh8f7e0 first]$ make
make -C /home/oct1158/Documents/Code/C/luckfox-pico/sysdrv/source/kernel M=/home/oct1158/Documents/Code/C/driver_test/first modules ARCH=arm CROSS_COMPILE=/home/oct1158/Documents/Code/C/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-
  CC [M]  /home/oct1158/Documents/Code/C/driver_test/first/test.o
  MODPOST /home/oct1158/Documents/Code/C/driver_test/first/Module.symvers
  LD [M]  /home/oct1158/Documents/Code/C/driver_test/first/test.ko
[oct1158@fed41-bh8f7e0 first]$
编译通过了，CC MODPOST LD等字样也能正常显示了。