sifive
Building Linux tools with buildroot
Buildroot has a Linux tools package BR2_PACKAGE_LINUX_TOOLS for building various utilities contained in the Linux tree. To enable this packages it seems to be required to build the Linux kernel itself with buildroot. Unfortunately, freedom-u-sdk currently builds the kernel independently of buildroot and only builds the userland with buildroot. Is there any specific reason why the kernel is not build with buildroot?
I encountered this issue because I wanted to enable perf (which is part of BR2_PACKAGE_LINUX_TOOLS) to make some performance benchmarks.
Note that freedom-u-sdk is not actively maintained. We use it for building demos to run on a hifive unleashed board, and we do the minimum amount of work necessary to keep this working.
I would guess a historical issue here. We probably had the linux kernel working first, and then we added buildroot to get a root file system. This would have been done a few years ago, and we never changed it because we never had any need to change it.
At the time we did this, buidlroot did not have RISC-V support, and we had to hack it to get it working. Since then, RISC-V support has been contributed upstream to buidlroot. You could try using buildroot directly instead of freedom-u-sdk. I've never tried this myself.
In general, if you want to do anything interesting, you are probably better off using a real linux distro rather than freedom-u-sdk. Fedora, debian, opensuse, open-embedded all have RISC-V support, and all have more features than freedom-u-sdk. open-embedded can give you an image that boots directly on a freedom unleashed board. For the others, if you edit the u-boot uEnv.txt file on the first partition, and install the linux distro rootfs on the second partition, you can use freedom-u-sdk to boot directly into any one of these real linux distros. I've done this. freedom-u-sdk comes with a debian rootfs that you can use for this. "make format-demo-image" copies a debian rootfs to the sdcard.
