Linux/RISC-V

This is a port of Linux kernel for the RISC-V instruction set architecture. Development is currently based on the 4.6 longterm branch.

Obtaining kernel sources

Master

Overlay the riscv architecture-specific subtree onto an upstream release:

    $ curl -L https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.6.2.tar.xz | tar -xJ
    $ cd linux-4.6.2
    $ git init
    $ git remote add -t master origin https://github.com/riscv/riscv-linux.git
    $ git fetch
    $ git checkout -f -t origin/master

Note that the -t <branch> option minimizes the history fetched. To add another branch:

    $ git remote set-branches --add origin <branch>
    $ git fetch

Full kernel source trees

For convenience, full kernel source trees are maintained on separate branches tracking linux-stable:

linux-4.6.y-riscv
linux-3.14.y-riscv (historical)

Building the kernel image

Create kernel configuration based on architecture defaults:
```
 $ make ARCH=riscv defconfig
```
Optionally edit the configuration via an ncurses interface:
```
 $ make ARCH=riscv menuconfig
```
Build the uncompressed kernel image:
```
 $ make -j4 ARCH=riscv vmlinux
```
Boot the kernel in the functional simulator, optionally specifying a raw disk image for the root filesystem:
```
 $ spike +disk=path/to/root.img bbl vmlinux
```
bbl (the Berkeley Boot Loader) is available from the riscv-pk repository.

Exporting kernel headers

The riscv-gnu-toolchain repository includes a copy of the kernel header files. If the userspace API has changed, export the updated headers to the riscv-gnu-toolchain source directory:

$ make ARCH=riscv headers_check
$ make ARCH=riscv INSTALL_HDR_PATH=path/to/riscv-gnu-toolchain/linux-headers headers_install

Rebuild riscv64-unknown-linux-gnu-gcc with the linux target: