Risc-V toolchain installation on mac

Risc-V_toolchain_installation_mac.md

Env: macOS Catalina 10.15.7

Step1: git clone --recursive https://github.com/riscv/riscv-gnu-toolchain

Although it doesn't need --recursive in README, this issue still happened on mac.

Step2: brew install python3 gawk gnu-sed gmp mpfr libmpc isl zlib expat

Step3: cd riscv-gnu-toolchain directory and ./configure --prefix=/opt/riscv --enable-multilib

To build either cross-compiler with support for both 32-bit and 64-bit

Step4: find your .zshrc, append this line export PATH="$PATH:/opt/riscv/bin" and then source .zshrc

DONE !!

After installing qemu sucessfully, let's start to build xv6-riscv

Step1: git clone git://github.com/mit-pdos/xv6-riscv-fall19.git
The xv6-riscv-fall19 repository differs slightly from the book's xv6-riscv in order to make the labs easier.

Step2: cd xv6-riscv-fall19 and make

Step3: make qemu

DONE !