test(verify): prove the arm64 lse atomics through the link-parity kernel

Assisted-by: GLM 5.3 Flash

verify/goobj_link_atomic_test.go

@@ -0,0 +1,60 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package verify
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+)
+
+// goobjAtomicMainSrc is the Go side of the LSE regression.  The kernel
+// drives a counter with LDADDALD and mixes the accumulated total; main
+// derives the same value in Go and panics on any divergence before
+// printing the deterministic line the baseline and the gasm-linked
+// binaries must agree on.
+const goobjAtomicMainSrc = `package main
+
+func caller(p *int64, addv int64, times int64) int64
+
+func main() {
+	addv, times := int64(3), int64(5)
+	v := int64(0)
+	got := caller(&v, addv, times)
+	oldsum, cur := int64(0), int64(0)
+	for i := int64(0); i < times; i++ {
+		oldsum += cur
+		cur += addv
+	}
+	k := uint64(0x9e3779b97f4a7c15)
+	want := int64(uint64(oldsum+cur) * k)
+	if got != want {
+		panic("atomic")
+	}
+	println("ok", caller(&v, addv, times))
+}
+`
+
+// TestGOOBJLinkAtomicKernel proves the arm64 LSE atomic families are proven
+// end to end: the kernel assembles by gasm into a GOOBJ object, substitutes
+// byte-wise into a real go build archive, relinks with cmd/link and the
+// linked binary computes the same atomic total as the toolchain-built one
+// under qemu-user, with the documented degradation on emulators without
+// LSE (the baseline run fails first and the claim drops to link-only).
+func TestGOOBJLinkAtomicKernel(t *testing.T) {
+	if testing.Short() {
+		t.Skip("builds the gasm binary and links Go programs")
+	}
+	if os.Getenv("GASM_LINK_PARITY") == "" {
+		t.Skip("deliberate verification: set GASM_LINK_PARITY=1 (just link-parity)")
+	}
+	goBin, err := exec.LookPath("go")
+	if err != nil {
+		t.Skip("no Go toolchain available")
+	}
+	gasmBin := buildLinkParityGasm(t, goBin)
+	t.Run("arm64", func(t *testing.T) {
+		goobjLinkKernel(t, goBin, gasmBin, "arm64", "linkatomic_arm64.s", goobjAtomicMainSrc)
+	})
+}