cpu: add riscv64 hwprobe drift test

Add a test that checks the Linux/riscv64 riscv_hwprobe constants, syscall
number, and pair layout copied into x/sys/cpu stay in sync with the
generated x/sys/unix sources.

The cpu package cannot depend on unix in production, but test files can
import it. Compare the copied definitions directly with unix rather than
parsing source files.

Updates golang/go#61416

Co-authored-by: YuanSheng <yuansheng@isrc.iscas.ac.cn>
Change-Id: I01407445099424b429d2494b63c05ef1bba746ef
Reviewed-on: https://go-review.googlesource.com/c/sys/+/800020
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

cpu/riscv64_hwprobe_test.go

diff --git a/cpu/riscv64_hwprobe_test.go b/cpu/riscv64_hwprobe_test.go
new file mode 100644
index 0000000..26ed42f
--- /dev/null
+++ b/cpu/riscv64_hwprobe_test.go
@@ -0,0 +1,73 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && riscv64
+
+package cpu
+
+import (
+	"testing"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+var (
+	_ int64  = riscvHWProbePairs{}.key
+	_ int64  = unix.RISCVHWProbePairs{}.Key
+	_ uint64 = riscvHWProbePairs{}.value
+	_ uint64 = unix.RISCVHWProbePairs{}.Value
+)
+
+func TestRISCV64HWProbeCopiedConstants(t *testing.T) {
+	copiedConsts := []struct {
+		name string
+		got  uint
+		want uint
+	}{
+		{"riscv_HWPROBE_KEY_IMA_EXT_0", riscv_HWPROBE_KEY_IMA_EXT_0, unix.RISCV_HWPROBE_KEY_IMA_EXT_0},
+		{"riscv_HWPROBE_IMA_C", riscv_HWPROBE_IMA_C, unix.RISCV_HWPROBE_IMA_C},
+		{"riscv_HWPROBE_IMA_V", riscv_HWPROBE_IMA_V, unix.RISCV_HWPROBE_IMA_V},
+		{"riscv_HWPROBE_EXT_ZBA", riscv_HWPROBE_EXT_ZBA, unix.RISCV_HWPROBE_EXT_ZBA},
+		{"riscv_HWPROBE_EXT_ZBB", riscv_HWPROBE_EXT_ZBB, unix.RISCV_HWPROBE_EXT_ZBB},
+		{"riscv_HWPROBE_EXT_ZBS", riscv_HWPROBE_EXT_ZBS, unix.RISCV_HWPROBE_EXT_ZBS},
+		{"riscv_HWPROBE_EXT_ZBC", riscv_HWPROBE_EXT_ZBC, unix.RISCV_HWPROBE_EXT_ZBC},
+		{"riscv_HWPROBE_EXT_ZVBB", riscv_HWPROBE_EXT_ZVBB, unix.RISCV_HWPROBE_EXT_ZVBB},
+		{"riscv_HWPROBE_EXT_ZVBC", riscv_HWPROBE_EXT_ZVBC, unix.RISCV_HWPROBE_EXT_ZVBC},
+		{"riscv_HWPROBE_EXT_ZVKB", riscv_HWPROBE_EXT_ZVKB, unix.RISCV_HWPROBE_EXT_ZVKB},
+		{"riscv_HWPROBE_EXT_ZVKG", riscv_HWPROBE_EXT_ZVKG, unix.RISCV_HWPROBE_EXT_ZVKG},
+		{"riscv_HWPROBE_EXT_ZVKNED", riscv_HWPROBE_EXT_ZVKNED, unix.RISCV_HWPROBE_EXT_ZVKNED},
+		{"riscv_HWPROBE_EXT_ZVKNHB", riscv_HWPROBE_EXT_ZVKNHB, unix.RISCV_HWPROBE_EXT_ZVKNHB},
+		{"riscv_HWPROBE_EXT_ZVKSED", riscv_HWPROBE_EXT_ZVKSED, unix.RISCV_HWPROBE_EXT_ZVKSED},
+		{"riscv_HWPROBE_EXT_ZVKSH", riscv_HWPROBE_EXT_ZVKSH, unix.RISCV_HWPROBE_EXT_ZVKSH},
+		{"riscv_HWPROBE_EXT_ZVKT", riscv_HWPROBE_EXT_ZVKT, unix.RISCV_HWPROBE_EXT_ZVKT},
+		{"riscv_HWPROBE_KEY_CPUPERF_0", riscv_HWPROBE_KEY_CPUPERF_0, unix.RISCV_HWPROBE_KEY_CPUPERF_0},
+		{"riscv_HWPROBE_MISALIGNED_FAST", riscv_HWPROBE_MISALIGNED_FAST, unix.RISCV_HWPROBE_MISALIGNED_FAST},
+		{"riscv_HWPROBE_MISALIGNED_MASK", riscv_HWPROBE_MISALIGNED_MASK, unix.RISCV_HWPROBE_MISALIGNED_MASK},
+	}
+
+	for _, c := range copiedConsts {
+		if c.got != c.want {
+			t.Errorf("%s = %#x, want %#x", c.name, c.got, c.want)
+		}
+	}
+}
+
+func TestRISCV64HWProbeCopiedSyscallNumber(t *testing.T) {
+	if sys_RISCV_HWPROBE != unix.SYS_RISCV_HWPROBE {
+		t.Errorf("sys_RISCV_HWPROBE = %#x, want %#x", sys_RISCV_HWPROBE, unix.SYS_RISCV_HWPROBE)
+	}
+}
+
+func TestRISCV64HWProbePairsLayout(t *testing.T) {
+	if got, want := unsafe.Sizeof(riscvHWProbePairs{}), unsafe.Sizeof(unix.RISCVHWProbePairs{}); got != want {
+		t.Errorf("riscvHWProbePairs size = %d, want RISCVHWProbePairs size = %d", got, want)
+	}
+	if got, want := unsafe.Offsetof(riscvHWProbePairs{}.key), unsafe.Offsetof(unix.RISCVHWProbePairs{}.Key); got != want {
+		t.Errorf("riscvHWProbePairs.key offset = %d, want RISCVHWProbePairs.Key offset = %d", got, want)
+	}
+	if got, want := unsafe.Offsetof(riscvHWProbePairs{}.value), unsafe.Offsetof(unix.RISCVHWProbePairs{}.Value); got != want {
+		t.Errorf("riscvHWProbePairs.value offset = %d, want RISCVHWProbePairs.Value offset = %d", got, want)
+	}
+}