gem5_FS.md

It's been a while since the last time I set up the full system mode of gem5 with Linux kernel. Recently I upgraded my desktop and finally gave it a chance to dual boot Ubuntu on a system installed with Windows 11. It worked but it means I will have to set up the system again.

So I installed RISC-V cross compiler following this link, which was what I followed a year ago, hoping to use such tool chain to cross compile the Linux kernel (this link); however, an error occurred:

csrs 0x100,s4', extension `zicsr' required

First try (did not work)

I found the corresponding issue here, and the solution I've tried so far is to pass this flag to the configure script: --with-arch=rv64gc

./configure --prefix=/opt/riscv --with-arch=rv64gc
sudo make linux

Second try (did not work)

./configure --prefix=/opt/riscv --with-arch=rv64gc_zicsr
sudo make linux

This link is useful: https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4

Third try (working solution)

First of all, we should build the riscv cross compiler following the instructions shown on the Github repo, i.e.

./configure --prefix=/opt/riscv
make linux

Then, when we try to build the Linux kernel, we should modify the Makefile. How to modify is based on this issue.

In linux.../arch/riscv/Makefile:

# Search for "KBUILD_AFLAGS += -march=", then append "_zicsr_zifencei"
# Search for "KBUILD_CFLAGS += -march=", then append "_zicsr_zifencei"
# In my case, I modified it to be the following:
KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))_zicsr_zifencei
KBUILD_AFLAGS += -march=$(riscv-march-y)_zicsr_zifencei

Then we are good to go.

Actually, the simplest way is to switch to an older version of riscv cross compiler. Follow the instructions here: https://gem5.googlesource.com/public/gem5-resources/+/HEAD/src/riscv-fs/README.md