Adding Custom Instructions to RISC-V GCC Toolchain

git clone [e-mail]:riscv-collab/riscv-gnu-toolchain.git
git submodule update --init --recursive

git clone [e-mail]:riscv/riscv-opcodes.git

Create a new file for the new instruction. We will use rv_zbme

testinst    rd rs1 rs2 31..25=1  14..12=0 6..2=0x1A 1..0=3

./parse.py -c ./unratified/rv_zbme

In the resulting encoding.out.h file, we can see the custom instruction:

encoding.out.h

/* Automatically generated by parse_opcodes. */
#ifndef RISCV_ENCODING_H
#define RISCV_ENCODING_H
#define MATCH_TESTINST 0x200006b
#define MASK_TESTINST 0xfe00707f

Then, we go to riscv-gnu-toolchain/binutils.

We need to edit the following files:

riscv-op.h

#define MATCH_TESTINST 0x200006b
#define MASK_TESTINST 0xfe00707f

DECLARE_INSN(testinst, MATCH_TESTINST, MASK_TESTINST)

riscv-op.c

{"testinst", 0, INSN_CLASS_I,       "d,s,t",         MATCH_TESTINST, MASK_TESTINST, match_opcode, 0 },

Make the same edit in

riscv-gnu-toolchain/gdb/opcodes/riscv-opc.c

riscv-gnu-toolchain/gdb/include/opcode/riscv-opc.h

Build

./configure --prefix=/scratch/tk/Desktop/riscv-matrix/riscv-unknown-elf/
make

./configure --prefix=/scratch/tk/Desktop/riscv-matrix/riscv-unknown-elf/ --with-cmodel=medany --enable-multilib

Example program

main.c

#include <stdint.h>
#include <stdio.h>


int main(void) {

  asm volatile("testinst x1, x0, x4\n");
  
  printf("hello\n");

  return 0;
}

riscv64-unknown-elf-gcc main.c -o main.elf

riscv64-unknown-elf-objdump -d main.elf > disassemble.S

Adding custom instructions compilation support, to RISCV toolchain.Medium

Adding Custom Instructions to the RISC-V GNU-GCC toolchain