Object code generation for new RISCV instruction emitted by LLVM backend

Question

From https://github.com/riscv/riscv-llvm,

Using the llvm-riscv is fairly simple to build a full executable however you need riscv64-unknown-*-gcc to do the assembling and linking. An example of compiling hello world:

$ clang -target riscv64 -mriscv=RV64IAMFD -S hello.c -o hello.S
$ riscv64-unknown-elf-gcc -o hello.riscv hello.S

My question is: if I change the LLVM backend and get it to emit a new instruction in the hello.S file, how will riscv64-unknown-elf-gcc know how to convert it into object code? Do I also need to make changes in riscv64-unknown-elf-gcc so that it knows the format of the new instruction?

Answer 1

riscv64-unknown-elf-gcc calls as, i.e. usually GNU as from the binutils to assemble assembly code (i.e. hello.S in your snippet) into executable machine code. Thus you would have to modify the binutils if you want to assemble a new instruction.