On Sun, 23 Nov 2014 16:25:11 +0800, 孙建希 said:
I found there's many files with same name in kernel. e.g: include/asm/linkage.h arch/x86/include/asm/linkage.h
I know when compile for x86, kbuild will use x86 linkage.h.
The secret is in the -I include directives - it will search for linkage.h in directories in order of -I on the compile command line, and use the first one it finds. So x86 gets built with "-I arch/x86/include/asm -I include/asm". The neat thing is that this allows a generic version for each .h to live in include/, and if a given architecthre FooVax doesn't use a custom version of that header, it finds it in include/,and if it *does* have a custom version, it finds it in -I arch/FooVax/include. (A nice benefit when porting - it means that even if you know that eventually you'll need a custom linkage.h due to the API, or whatever, you can still do compile-testing of other code while you're still writing linkage.h) To see the compile command line in gory detail, use 'make V=1'.