Reference:https://xpack.github.io/blog/2022/05/18/riscv-none-elf-gcc-v12-1-0-2-released/
RISC-V ISA updates
Compared to previous releases, starting from 12.x, the compiler implements the new RISC-V ISA, which introduces an incompatibility issue, and builds might throw error messages like unrecognized opcode csrr.
The reason is that csr read/write (csrr*/csrw*) instructions and fence.i instruction were separated from the I extension, becoming two standalone extensions: Zicsr and Zifencei.
The solution is to add _zicsr and/or _zifencei to the -march option, e.g. -march=rv32imac becomes -march=rv32imac_zicsr_zifencei.
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