根据.config剥离Linux内核源代码 [英] Strip Linux kernel sources according to .config

问题描述

是否有任何有效的方法(也许是通过滥用gcc预处理器?)来获取一组剥离的内核源，其中没有根据.config不需要的所有代码?

Is there any efficient way (maybe by abusing the gcc preprocessor?) to get a set of stripped kernel sources where all code not needed according to .config is left out?

推荐答案

很好地采取了一些措施.

Well got some steps into a solution.

首先，可以通过

make KBUILD_VERBOSE=1 | tee build.log
grep '^  gcc' build.log

现在，我仅选择一个gcc命令行以进行进一步的操作.例如，kernel/kmod.c的构建看起来像:

For now, I select only one gcc command line for further steps. For example the build of kernel/kmod.c, it looks like:

gcc <LIST OF MANY OPTIONS> -c -o kernel/kmod.o kernel/kmod.c

我现在删除选项-c，-o ...并添加-E，从而禁用编译并将预处理器输出写入屏幕.此外，我添加了-fdirectives-only来防止宏扩展，并添加了-undef来删除GNU定义的宏定义.内核makefile已添加-nostdinc删除标准c标头.

I now remove the option -c, -o ... and add -E, thus disabling compilation and writing preprocessor output to the screen. Further I add -fdirectives-only to prevent macro expansion and -undef to remove the GNU defined macro definitions. -nostdinc to remove the standard c headers is already added by the kernel makefile.

现在包括仍然包括在内，因此在预处理器输出上进行了扩展.因此，我通过grep通过管道将输入文件删除:grep -v '#include' kernel/kmod.c.现在只剩下一个include:Makefile的命令行中包含了autoconf.h.这很棒，因为它实际上定义了#ifdef CONFIG_...用来选择活动内核代码的宏.

Now includes are still included and thus expanded on the preprocessor output. Thus I pipe the input file through grep removing them: grep -v '#include' kernel/kmod.c. Now only one include is left: autoconf.h is included by the Makefile's command line. This is great as it actually defines the macros used by #ifdef CONFIG_... to select the active kernel code.

剩下的唯一事情就是通过grep -v '^#'从autoconf.h中过滤出预处理程序注释和其余的#define.

The only thing left is to filter out the preprocessor comments and the remaining #defines from autoconf.h by means of grep -v '^#'.

整个管道看起来像:

grep -v '#include' kernel/kmod.c | gcc -E -fdirectives-only -undef <ORIGINAL KERNEL BUILD GCC OPTIONS WITHOUT -c AND -o ...> - |grep -v '^#'

，结果是kernel/kmod.c的过滤版本，其中包含实际上内置在kmod.o中的代码.

and the result is a filtered version of kernel/kmod.c containing the code that is actually build into kmod.o.

问题仍然存在:如何对整个源代码树执行此操作?是否存在实际上在构建但从未使用过并且在链接时被删除的文件?

Questions remain: How to do that for the whole source tree? Are there files that are actually build but never used and stripped at linking?

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