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Backports provide drivers released on newer kernels backported for usage on older kernels. There are two versions of linux-backports: one that supports Linux kernels >= 3.0 and one supports even older kernels. We're only packaging the version that supports >= 3.0. linux-backports needs to have access to the kernel's .config to extract information it reintroduces as blind options in generated Kconfig snippets for its own menuconfig. However, Buildroot offers no way to express this kind of dependency. So we need to hand-write a dependency from linux-backports' own .config to linux' .config . Since linux.mk has not already been sourced by the time we source linux-backports.mk, we are missing the definition for LINUX_DIR, so we can not use it our rule. Fortunately, make provides so-called "secondary expansion", by which rules which dependencies include a $$-dereferenced variable wil lbe re-evaluated after all the rest of the Makefiles have been parsed. So, we use that secondary expansion to post-pone evaluation of that dependency so we can use LINUX_DIR. Note: reconstructing LINUX_DIR by hand does not work, because of the custom archives, git tree, or override-srcdir. Signed-off-by: Petr Vorel <petr.vorel@gmail.com> Cc: Arnout Vandecappelle <arnout@mind.be> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Cc: "Yann E. MORIN" <yann.morin.1998@free.fr> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr> Reviewed-by: Romain Naour <romain.naour@openwide.fr> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Buildroot is a simple, efficient and easy-to-use tool to generate embedded Linux systems through cross-compilation. The documentation can be found in docs/manual. You can generate a text document with 'make manual-text' and read output/docs/manual/manual.text. Online documentation can be found at http://buildroot.org/docs.html To build and use the buildroot stuff, do the following: 1) run 'make menuconfig' 2) select the target architecture and the packages you wish to compile 3) run 'make' 4) wait while it compiles 5) find the kernel, bootloader, root filesystem, etc. in output/images You do not need to be root to build or run buildroot. Have fun! Buildroot comes with a basic configuration for a number of boards. Run 'make list-defconfigs' to view the list of provided configurations. Please feed suggestions, bug reports, insults, and bribes back to the buildroot mailing list: buildroot@buildroot.org You can also find us on #buildroot on Freenode IRC.