c - obj-y += something/in linux kernel Makefile 是什么意思？

Question

我明白了

的意思

obj-$(CONFIG_USB)       += usb.o

如果 CONFIG_USB 是 y 那么 usb.o 将被编译。那么现在如何理解这个

obj-y               += something/

Answer 1

内核 Makefile 是 kbuild 系统的一部分，记录在网络上的各个地方，例如 http://lwn.net/Articles/21835/ .相关摘录在这里:

--- 3.1 Goal definitions

Goal definitions are the main part (heart) of the kbuild Makefile. These lines define the files to be built, any special compilation options, and any subdirectories to be entered recursively.

The most simple kbuild makefile contains one line:

Example: obj-y += foo.o

This tell kbuild that there is one object in that directory named foo.o. foo.o will be build from foo.c or foo.S.

If foo.o shall be built as a module, the variable obj-m is used. Therefore the following pattern is often used:

Example: obj-$(CONFIG_FOO) += foo.o

$(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). If CONFIG_FOO is neither y nor m, then the file will not be compiled nor linked.

所以 m 表示模块，y 表示内置(在内核配置过程中代表是)，$(CONFIG_FOO) 从正常中提取正确答案配置过程。