编译内核模块遇asm头文件缺失：软链接无法解决多依赖问题

问题描述 #

我尝试编译一个最小化内核模块，使用如下Makefile：

obj-m += mymodule.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

编译时出现头文件找不到的错误，我创建软链接解决了第一个问题，但随后又遇到另一个头文件缺失的问题，而一个软链接无法同时指向两个路径。我的理解是否有误？该如何解决此问题？

编译错误日志与操作记录 #

root@system-yocto:~/kernelModule# make -j
make -C /lib/modules/5.15.54-yocto-standard/build M=/home/root/kernelModule modules
make[1]: Entering directory '/lib/modules/5.15.54-yocto-standard/build'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: arm-poky-linux-gnueabi-gcc (GCC) 11.4.0
  You are using:           gcc (GCC) 11.4.0
  CC [M]  /home/root/kernelModule/mymodule.o
In file included from ./include/linux/init.h:5,
                 from /home/root/kernelModule/mymodule.c:1:
./include/linux/compiler.h:255:10: fatal error: asm/rwonce.h: No such file or directory
  255 | #include <asm/rwonce.h>
      |          ^~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [scripts/Makefile.build:288: /home/root/kernelModule/mymodule.o] Error 1
make[1]: *** [Makefile:1886: /home/root/kernelModule] Error 2
make[1]: Leaving directory '/lib/modules/5.15.54-yocto-standard/build'
make: *** [Makefile:4: all] Error 2
root@system-yocto:~/kernelModule# ls -l /lib/modules/5.15.54-yocto-standard/source/include/
total 204
drwxr-xr-x  3 root root  4096 Mar  9 12:34 acpi
drwxr-xr-x  4 root root  4096 Mar  9 12:42 asm-generic
drwxr-xr-x  2 root root  4096 Mar  9 12:34 clocksource
drwxr-xr-x  2 root root 53248 Mar  9 12:34 config
drwxr-xr-x  3 root root  4096 Mar  9 12:34 crypto
drwxr-xr-x  5 root root  4096 Mar  9 12:34 drm
drwxr-xr-x 37 root root  4096 Mar  9 12:34 dt-bindings
drwxr-xr-x  3 root root  4096 Mar  9 12:34 generated
drwxr-xr-x  2 root root  4096 Mar  9 12:34 keys
drwxr-xr-x  2 root root  4096 Mar  9 12:34 kunit
drwxr-xr-x  2 root root  4096 Mar  9 12:34 kvm
drwxr-xr-x 65 root root 40960 Mar  9 12:34 linux
drwxr-xr-x  2 root root  4096 Mar  9 12:34 math-emu
drwxr-xr-x  6 root root  4096 Mar  9 12:34 media
drwxr-xr-x  2 root root  4096 Mar  9 12:34 memory
drwxr-xr-x  2 root root  4096 Mar  9 12:34 misc
drwxr-xr-x 12 root root  4096 Mar  9 12:34 net
drwxr-xr-x  2 root root  4096 Mar  9 12:34 pcmcia
drwxr-xr-x  2 root root  4096 Mar  9 12:34 ras
drwxr-xr-x  2 root root  4096 Mar  9 12:34 rdma
drwxr-xr-x  3 root root  4096 Mar  9 12:34 scsi
drwxr-xr-x 16 root root  4096 Mar  9 12:34 soc
drwxr-xr-x  4 root root  4096 Mar  9 12:34 sound
drwxr-xr-x  3 root root  4096 Mar  9 12:34 target
drwxr-xr-x  3 root root  4096 Mar  9 12:34 trace
drwxr-xr-x 12 root root  4096 Mar  9 12:34 uapi
drwxr-xr-x  2 root root  4096 Mar  9 12:34 vdso
drwxr-xr-x  2 root root  4096 Mar  9 12:34 video
drwxr-xr-x  4 root root  4096 Mar  9 12:34 xen
root@system-yocto:~/kernelModule# ln -s /lib/modules/5.15.54-yocto-standard/source/include/asm-generic/ /lib/modules/5.15.54-yocto-standard/source/include/asm
root@system-yocto:~/kernelModule# make -j
make -C /lib/modules/5.15.54-yocto-standard/build M=/home/root/kernelModule modules
make[1]: Entering directory '/lib/modules/5.15.54-yocto-standard/build'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: arm-poky-linux-gnueabi-gcc (GCC) 11.4.0
  You are using:           gcc (GCC) 11.4.0
  CC [M]  /home/root/kernelModule/mymodule.o
In file included from ./include/linux/errno.h:5,
                 from ./include/linux/string.h:8,
                 from ./include/linux/bitmap.h:10,
                 from ./include/linux/cpumask.h:12,
                 from ./include/linux/mm_types_task.h:14,
                 from ./include/linux/mm_types.h:5,
                 from ./include/linux/buildid.h:5,
                 from ./include/linux/module.h:14,
                 from /home/root/kernelModule/mymodule.c:2:
./include/uapi/linux/errno.h:1:10: fatal error: asm/errno.h: No such file or directory
    1 | #include <asm/errno.h>
      |          ^~~~~~~~~~~~~
compilation terminated.
make[2]: *** [scripts/Makefile.build:288: /home/root/kernelModule/mymodule.o] Error 1
make[1]: *** [Makefile:1886: /home/root/kernelModule] Error 2
make[1]: Leaving directory '/lib/modules/5.15.54-yocto-standard/build'
make: *** [Makefile:4: all] Error 2

问题根源与解决方法 #

你的理解没错，单个软链接确实无法同时指向两个路径，核心问题在于Yocto环境下内核头文件包不完整，或者/lib/modules/$(uname -r)/build指向的内核源码缺少对应架构的asm目录。以下是可行的解决步骤：

1. 安装完整内核头文件包 #

在Yocto系统中，必须安装对应内核版本的kernel-dev包，执行命令：

opkg install kernel-dev-5.15.54-yocto-standard

注意替换版本号为uname -r输出的实际内核版本。

2. 验证内核源码链接 #

确认/lib/modules/$(uname -r)/build和/lib/modules/$(uname -r)/source指向完整的内核源码目录。如果链接错误，重新创建：

rm -f /lib/modules/5.15.54-yocto-standard/build
ln -s /path/to/your/complete/kernel/source /lib/modules/5.15.54-yocto-standard/build

3. 使用Yocto交叉编译工具链（推荐） #

当前使用的gcc与内核编译时的arm-poky-linux-gnueabi-gcc不一致，后续易出现兼容性问题。正确做法是使用Yocto提供的交叉编译环境：

• 加载Yocto环境变量：

  source /path/to/yocto/build/environment-setup-armv7at2hf-neon-poky-linux-gnueabi
  

• 修改Makefile，指定交叉编译器：

  obj-m += mymodule.o
  ARCH=arm
  CROSS_COMPILE=arm-poky-linux-gnueabi-
  
  all:
          make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
  clean:
          make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
  

• 重新执行make编译。

4. 临时应急修复（不推荐长期使用） #

若无法安装完整头文件包，可手动创建asm目录并合并头文件：

mkdir -p /lib/modules/5.15.54-yocto-standard/source/include/asm
cp -r /lib/modules/5.15.54-yocto-standard/source/include/asm-generic/* /lib/modules/5.15.54-yocto-standard/source/include/asm/
# 复制对应架构的asm头文件，例如从Yocto构建目录获取arm架构内容
cp -r /path/to/yocto/build/tmp/work-shared/.../linux-yocto/include/asm/* /lib/modules/5.15.54-yocto-standard/source/include/asm/

此方法易引发头文件冲突，仅作临时方案。

内容的提问来源于stack exchange，提问作者ohiliouh