Created attachment 9586 [details] Example of the difference between the linux and linux-headers trees following an extension being applied. Linux extensions are a mechanism for providing new features through modification to the Linux kernel tree. This is usually in the form of patches or new files from an out-of-tree source. (See Buildroot manual section 18.22.2. linux-kernel-extensions). Currently during a build the Linux extensions are applied to the linux source tree, but not the linux-headers source tree. In comparison, the global and Linux patch directories are applied to both the linux and linux-headers source trees. This can lead issues where the source of the linux-headers does not represent the kernel running on the target - For example, linux-headers is consumed by most C libraries. I have encountered this when attempting to write a patch that modifies an applied kernel extension. The patch fails to apply to linux-headers as the source files added by the extension do not exist. This can be reproduced this by enabling a Linux extension (I've tested with fbtft and ev3dev-linux-drivers) and performing a build, then comparing the linux and linux-headers build directories - I have attached a diff example showing the additions in one source tree but not the other.
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