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Evaluating all the <PKG>_RECURSIVE_FINAL_DEPENDENCIES variables (abbreviated RFD hereafter) ends up being quite slow. Enough, on a reasonable modern workstation, to increase the time it takes to run "make printvars" from 13 seconds in 2018.02 to 371 seconds in 2019.02. This patch improves this by using dynamic programming to speed the evaluation of RFD, reducing the before mentioned printvars time to about 14.6 seconds. The evaluation of PKG1_RFD requires recursively evaluating each of PKG1's dependencies' RFDs, then their dependencies' RFDs, and so on. The same is done for PKG2_RFD. But it's likely that many of the dependencies of PKG2 are the same as PKG1. And when we consider all packages, the dependencies are re-computed many thousands of times. To avoid this re-computation we memoize, or save, the computed value of each RFD variable when it found the first time. Subsequent evaluations re-use the memoized value. Surprisingly, this ends up being not all the hard to implement in make. The basic construct is this: VAR = $(if !defined(VAR__X),$(eval VAR__X := value))$(VAR__X) The first time VAR is evaluated VAR__X will not be defined, and code to set VAR__X to the computed value is eval'd. Then the now defined value of VAR__X is returned. Subsequent evaluations can just return VAR__X. It is important to note that VAR is defined with '=', as not enough information (namely, all packages' dependencies) is know when it is parsed to find the correct value. VAR will be evaluated each time it is used. But VAR__X is defined with ":=", so that it is evaluated once when defined, and not each time it is used. Signed-off-by: Trent Piepho <tpiepho@impinj.com> Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Signed-off-by: Peter Korsgaard <peter@korsgaard.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. If you would like to contribute patches, please read https://buildroot.org/manual.html#submitting-patches