question about adding "mod" instruction

[WilliamWangPeng]

Hi dear all
I have added the corresponding shell commands to riscv-gdb as well, and followed the four steps at
https://nitish2112.github.io/post/adding-instruction-riscv/
In the riscv-isa-sim/riscv/encoding.h add the following lines:

#define MATCH_MOD 0x200006b
#define MASK_MOD 0xfe00707f
...
DECLARE_INSN(add, MATCH_MOD, MASK_MOD)
Create a file riscv-isa-sim/riscv/insns/mod.h and add these lines:

WRITE_RD(sext_xlen(RS1 % RS2));
Add this file to riscv-isa-sim/riscv/riscv.mk.in

riscv_insn_list =
...
mod
...
In riscv-isa-sim/spike_main/disasm.cc add the following lines:

DEFINE_RTYPE(mod);
and I meet with new errors like the picture one(mod.cc failed) and in riscv-isa-sim there are many .cc,.o and .d of some instructions in picture two.

if I put the shell command "spike pk mod", where mod is the elf, which will occur "an illegal instruction was executed" shown in picture two.

[WilliamWangPeng]

by the way
I have already changed
DECLARE_INSN(add, MATCH_MOD, MASK_MOD)
to
DECLARE_INSN(mod, MATCH_MOD, MASK_MOD)

[jim-wilson]

Spike isn't part of the toolchain, and the instructions you are following are out of date. But the problem seems obvious from your screen shot. Compare the MATCH_MOD sed command on the last line to the MATCH_AND sed command one line above. Then figure out how to fix it.

[WilliamWangPeng]

Spike isn't part of the toolchain, and the instructions you are following are out of date. But the problem seems obvious from your screen shot. Compare the MATCH_MOD sed command on the last line to the MATCH_AND sed command one line above. Then figure out how to fix it.

thank you dear Jim
I have delete "//new added" which informs me of new added instruction but made the rebuilding error, cause the compiler may misunderstand this in the rebuilding process. At the same time, I added
#define match_mod 0x200006b
#define mask_mod 0xfe00707f
in disasm.cc. After that, there will not be errors like
"disasm.cc ::error, "match_mod" was not declared in this scope"when rebuilding Spike.
finally, I put
riscv64-unknown-elf-gcc -o mod mod.c
spike pk mod
Spike appears

[aswaterman]

Are you sure that the spike that's in your PATH is the same one you just built? What that dump is saying is that 02e787eb is an illegal instruction, but in fact that pattern corresponds to the new instruction you've added. So I would expect this program to execute correctly. Perhaps you forgot to make install, or the install path isn't in your PATH?

[WilliamWangPeng]

Are you sure that the spike that's in your PATH is the same one you just built? What that dump is saying is that 02e787eb is an illegal instruction, but in fact that pattern corresponds to the new instruction you've added. So I would expect this program to execute correctly. Perhaps you forgot to make install, or the install path isn't in your PATH?

thank you for your advice, dear Andrew.
I use the testing program provided by Nitish
https://nitish2112.github.io/post/adding-instruction-riscv/
and now
when I run "spike pk mod", it works.

[TommyMurphyTM1234]

This is a list of all issues logged that I can find that relate to adding new instructions to the toolchain:

• How to add support for a new instruction? #1095
• Adding custom instruction to vector compiler #1055
• Adding custom instruction to the elf tool-chain #837
• How to Add custom instructions to riscv-elf-toolchain #782
• Adding rvv intrinsic to already installed toolchain #1003
• How to add a custom non-standard instruction type format #795
• how can I modify functionality of an instruction? #660
• question about adding "mod" instruction #543
• Searching for explainations to define a new instruction in the "struct riscv-opcode " #341
• adding new opode extensions #115

At this stage in the evolution of RISC-V,the majority of instruction addition will be done under the auspices of the relevant groups working on standardising, prototyping, and implementing/enhancing RISC-V extensions and their corresponding instructions. As such, there should be less of a demand for others to do so.

However, where somebody still wants to implement a non stadard custom extension/instruction here are some useful resources:

• GCC internals documentation: https://gcc.gnu.org/onlinedocs/gccint/
• https://hsandid.github.io/posts/risc-v-custom-instruction/
• https://ossg.bcs.org/blog/2020/10/29/adding-an-instruction-to-the-gnu-assembler/
• https://embdev.net/topic/228773
• https://groups.google.com/u/0/a/groups.riscv.org/g/sw-dev/c/sL_OHXYj3LY/m/NOm5Fwa3BAAJ
• https://forums.sifive.com/t/adding-custom-instruction-to-riscv-toolchain/4044/2