交叉编译外部linux模块:M= ' pwd '目录未找到

I'm compiling an external module against a complete kernel tree using CentOS. I've succesfully modified, cross-compiled, built and booted this kernel on a Beaglebone. I'm using the linaro tools (arm-gnueabihf-). I'm using the same typical Makefile structure to compile the module I've ever used since 2.6 came out. When running the make rule:I'm compiling an external module against a comp