env GOARCH=riscv64
env GORISCV64=rva20u64
go list -f '{{context.ToolTags}}'
stdout 'riscv64.rva20u64'

env GOARCH=riscv64
env GORISCV64=rva22u64
go list -f '{{context.ToolTags}}'
stdout 'riscv64.rva20u64 riscv64.rva22u64'

env GOARCH=riscv64
env GORISCV64=rva22
! go list -f '{{context.ToolTags}}'
stderr 'go: invalid GORISCV64: must be rva20u64, rva22u64'

env GOARCH=riscv64
env GORISCV64=

	if goamd64(); Error == nil {
		t.Errorf("Wrong parsing of GOAMD64=1")
	}

	os.Setenv("GORISCV64", "rva20u64")
	if goriscv64() != 20 {
		t.Errorf("Wrong parsing of RISCV64=rva20u64")
	}
	os.Setenv("GORISCV64", "rva22u64")
	if goriscv64() != 22 {
		t.Errorf("Wrong parsing of RISCV64=rva22u64")
	}
	Error = nil
	os.Setenv("GORISCV64", "rva22")
	if _ = goriscv64(); Error == nil {

The `GORISCV64` environment variable defaults to `rva20u64`.

### Wasm {#wasm}

<!-- go.dev/issue/63718 -->
The `go_wasip1_wasm_exec` script in `GOROOT/misc/wasm` has dropped support

	return int(defaultGOPPC64[len("power")] - '0')
}

func goriscv64() int {
	switch v := envOr("GORISCV64", defaultGORISCV64); v {
	case "rva20u64":
		return 20
	case "rva22u64":
		return 22
	}
	Error = fmt.Errorf("invalid GORISCV64: must be rva20u64, rva22u64")
	v := defaultGORISCV64[len("rva"):]
	i := strings.IndexFunc(v, func(r rune) bool {
		return r < '0' || r > '9'
	})
	year, _ := strconv.Atoi(v[:i])