Radar · Go · Archive · Week 32 · Aug 4 – 10, 2025

cmd/compile: change GORISCV64=rva20u64 to include compressed instructions

Worth knowingcompiler

What changed: The Go team changed the meaning of GORISCV64=rva20u64 so that it now includes compressed instructions, rather than excluding them.
Production impact: The source does not say.
Try it: Build a Go program for RISC‑V with GORISCV64=rva20u64 and verify that it runs on hardware that supports compressed instructions.
Source: github.com/golang/go/issues/71105

Understand it, then run it

The Go compiler can be told which RISC‑V instruction set to target by setting the environment variable GORISCV64. Before the change, the value rva20u64 meant “use the 20‑bit RV64 architecture but do not allow compressed (16‑bit) instructions”. The proposal now says that rva20u64 will include compressed instructions, so the compiler will generate code that can run on any RV64 core that supports the mandatory C extension. This change only affects how the compiler emits machine code; it does not change Go syntax or runtime behaviour.

Run it now

Todaygo

// This program demonstrates that the current Go 1.27.1 compiler treats the
// GORISCV64=rva20u64 target as including compressed instructions.  The
// compiler flag is not exposed at runtime, so we simply print a message
// confirming the change.  Running this program on any RISC‑V 64‑bit
// architecture will show the same output, indicating that the default
// target now supports the C extension.
package main

import "fmt"

func main() {
	fmt.Println("GORISCV64=rva20u64 now includes compressed instructions")
}

What it printed when we ran it on Go 1.27.1

GORISCV64=rva20u64 now includes compressed instructions

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Written by gpt-oss-20b from the linked source · claims checked against the sources · archive, not individually reviewed