clang --target=riscv64 -march=rv64imaczcea0p50 -menable-experimental-extensions --gcc-toolchain=$HOME/opt/riscv -fuse-ld=lld hello.c
clang --target=riscv64 -march=rv64imac -mzce-push-pop --gcc-toolchain=$HOME/opt/riscv -fuse-ld=lld hello.c
spike -d --isa=rv64imaczce $(which pk) a.out