Compile error for custom0 custom instruction - riscv

Question

I'm trying to design simple accelerator to be familiar with RoCC and its interface in spike, and access it through RoCC command(such as custom0, custom1, ...)
In fact, I follow some guides described in cs250 lab4 from Berkeley by using master branch of riscv tools.(Actually, guides are different from this, but I could understand basic ideas, so I go through it.)
However, it seems that it does not work well.
First of all, I just build riscv tools in repository, and then I tried to compile dummy_rocc_test.c which resides in riscv-isa-sim/dumy_rocc
but it produces following outputs when using command:
riscv64-unknown-elf-gcc -o d ./dummy_rocc_test.c
./dummy_rocc_test.c: Assembler messages:
./dummy_rocc_test.c:13: Error: unrecognized opcode `custom0 x0,a5,2,0'
./dummy_rocc_test.c:15: Error: unrecognized opcode `custom0 a5,x0,2,1'
./dummy_rocc_test.c:18: Error: unrecognized opcode `custom0 x0,a5,2,3'
./dummy_rocc_test.c:20: Error: unrecognized opcode `custom0 a5,x0,2,1'
./dummy_rocc_test.c:23: Error: unrecognized opcode `custom0 x0,a5,2,2'
./dummy_rocc_test.c:24: Error: unrecognized opcode `custom0 x0,a5,2,3'
./dummy_rocc_test.c:25: Error: unrecognized opcode `custom0 a5,x0,2,1'
Did I miss something before compiling this? or Should I have to modify some build option even though I want to use dummy extension?

Answer 1

By default recognition of custom0/custom1 is off.
Try to use -march option with custom suffix:
riscv64-unknown-elf-gcc -march=rv64imafdxcustom -o d ./dummy_rocc_test.c
Note: old toolchain use upper case ISA extensions symbols, i.e:
-march=RV64IMAFDXcustom