fix(verify): isolate smoke and abi sweeps in a child process

Assisted-by: GLM 5.3

cmd/gasm/main.go

@@ -1051,7 +1051,8 @@ decoders) that crash on random input but should succeed on valid data.
 	groundTruth := fs.Bool("ground-truth", false, "compare machine code byte-for-byte against go tool asm")
 	fuzz := fs.Bool("fuzz", false, "differential fuzz: JIT both gasm and go-tool-asm versions, compare outputs")
 	fuzzN := fs.Int("n", 1000, "number of fuzz iterations per function")
-	fuzzOne := fs.String("fuzz-one", "", "") // hidden: fuzz a single function (subprocess mode)
+	fuzzOne := fs.String("fuzz-one", "", "")   // hidden: fuzz a single function (subprocess mode)
+	sweepOne := fs.String("sweep-one", "", "") // hidden: smoke/abi a single function (subprocess mode)
 	call := fs.String("call", "", "call a single function with -buf instead of the sweeps")
 	bufSpec := fs.String("buf", "", "buffer spec for -call: name:size:pattern[,name:size:pattern] (zero, ones, seq, or hex)")
 	repeat := fs.Int("repeat", 1, "number of times to repeat a -call invocation")
@@ -1126,6 +1127,25 @@ decoders) that crash on random input but should succeed on valid data.
 		return 0
 	}
 
+	// Subprocess mode: run the smoke/abi checks for a single function and
+	// exit with the accumulated status.  The parent interprets a clean exit
+	// as success, a non-zero exit as failure and death-by-signal as a crash.
+	if *sweepOne != "" {
+		fl, err := k.Func(*sweepOne)
+		if err != nil || !fl.NoSplit {
+			fmt.Fprintf(os.Stderr, "gasm verify: %s: %v\n", *sweepOne, err)
+			return 1
+		}
+		msgs, failed := runSweepChecks(k, path, *sweepOne, fl, *smoke, *abi, *abiN)
+		for _, m := range msgs {
+			fmt.Println(m)
+		}
+		if failed {
+			return 1
+		}
+		return 0
+	}
+
 	// Ground-truth comparison: assemble with go tool asm and compare bytes.
 	if *groundTruth {
 		gt, err := verify.GroundTruth(path)
@@ -1241,7 +1261,10 @@ decoders) that crash on random input but should succeed on valid data.
 		}
 	}
 
-	// Run smoke and ABI checks in parallel.
+	// Run smoke and ABI checks in parallel, each function in its own child
+	// process: the JIT'd code runs with zeroed or fuzzed arguments, and a
+	// function that dereferences them faults — the crash is reported as a
+	// CRASH line instead of killing this process (mirrors fuzzInSubprocess).
 	if *smoke || *abi {
 		type checkResult struct {
 			name string
@@ -1259,53 +1282,16 @@ decoders) that crash on random input but should succeed on valid data.
 				continue
 			}
 			wg.Add(1)
-			go func(name string, fl asm.FuncLayout) {
+			go func(name string) {
 				defer wg.Done()
 				sem <- struct{}{}
 				defer func() { <-sem }()
 
-				var msgs []string
+				msg, fail := sweepInSubprocess(path, name, *smoke, *abi, *abiN)
-				failed := false
-
-				if *smoke {
-					args := make([]byte, fl.Args)
-					_, err := k.CallFunc(name, args)
-					if err != nil {
-						msgs = append(msgs, fmt.Sprintf("    smoke: FAIL — %v", err))
-						failed = true
-					} else {
-						msgs = append(msgs, "    smoke: OK")
-					}
-				}
-
-				if *abi {
-					if src, err := readSource(path); err == nil {
-						result := k.FuzzFuncCheckedByName(name, src, *abiN, int64(*abiN))
-						if result.Mismatches > 0 {
-							msgs = append(msgs, fmt.Sprintf("    abi: %s", result))
-							failed = true
-						} else {
-							msgs = append(msgs, fmt.Sprintf("    abi: clean (%d varied inputs)", result.Matches))
-						}
-					} else {
-						args := make([]byte, fl.Args)
-						_, report, err := k.CallFuncChecked(name, args)
-						if err != nil {
-							msgs = append(msgs, fmt.Sprintf("    abi: FAIL — %v", err))
-							failed = true
-						} else if !report.OK() {
-							msgs = append(msgs, fmt.Sprintf("    abi: %s", report))
-							failed = true
-						} else {
-							msgs = append(msgs, "    abi: clean")
-						}
-					}
-				}
-
 				mu.Lock()
-				results = append(results, checkResult{name: name, msg: strings.Join(msgs, "\n"), fail: failed})
+				results = append(results, checkResult{name: name, msg: msg, fail: fail})
 				mu.Unlock()
-			}(name, fl)
+			}(name)
 		}
 		wg.Wait()
 
@@ -1363,6 +1349,96 @@ func fuzzInSubprocess(path, funcName string, n int) string {
 	return strings.TrimSpace(string(out))
 }
 
+// sweepInSubprocess runs the smoke/abi checks for a single function in a
+// child process.  If the child is killed by a signal (e.g. SIGSEGV from a
+// function that dereferences its zeroed or fuzzed arguments), it returns a
+// CRASH report instead of dying — the same isolation fuzzInSubprocess
+// provides for the fuzz sweep.
+func sweepInSubprocess(path, funcName string, smoke, abi bool, abiN int) (string, bool) {
+	self, err := os.Executable()
+	if err != nil {
+		return fmt.Sprintf("    smoke/abi: FAIL — cannot find self: %v", err), true
+	}
+	args := []string{"verify", "--sweep-one=" + funcName}
+	if smoke {
+		args = append(args, "-smoke")
+	}
+	if abi {
+		args = append(args, "-abi", "-abi-n", strconv.Itoa(abiN))
+	}
+	args = append(args, path)
+	cmd := exec.Command(self, args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			ws, ok := exitErr.Sys().(syscall.WaitStatus)
+			if ok && ws.Signaled() {
+				return fmt.Sprintf("    smoke/abi: CRASH (%v — the function faults on zeroed or fuzzed\n    arguments; verify it with -call and valid buffers)", ws.Signal()), true
+			}
+		}
+		// Non-zero exit without a signal: the checks themselves failed and
+		// the child already printed the diagnostic lines.
+		return sweepCheckLines(out), true
+	}
+	return sweepCheckLines(out), false
+}
+
+// sweepCheckLines extracts the check-result lines from child output,
+// dropping the child's own file/function banners (the parent prints those).
+func sweepCheckLines(out []byte) string {
+	var lines []string
+	for _, l := range strings.Split(string(out), "\n") {
+		t := strings.TrimSpace(l)
+		if strings.HasPrefix(t, "smoke:") || strings.HasPrefix(t, "abi:") {
+			lines = append(lines, "    "+t)
+		}
+	}
+	return strings.Join(lines, "\n")
+}
+
+// runSweepChecks performs the in-process smoke and ABI checks for one
+// function — the child half of sweepInSubprocess.
+func runSweepChecks(k *verify.Kernel, path, name string, fl asm.FuncLayout, smoke, abi bool, abiN int) ([]string, bool) {
+	var msgs []string
+	failed := false
+
+	if smoke {
+		args := make([]byte, fl.Args)
+		_, err := k.CallFunc(name, args)
+		if err != nil {
+			msgs = append(msgs, fmt.Sprintf("    smoke: FAIL — %v", err))
+			failed = true
+		} else {
+			msgs = append(msgs, "    smoke: OK")
+		}
+	}
+
+	if abi {
+		if src, err := readSource(path); err == nil {
+			result := k.FuzzFuncCheckedByName(name, src, abiN, int64(abiN))
+			if result.Mismatches > 0 {
+				msgs = append(msgs, fmt.Sprintf("    abi: %s", result))
+				failed = true
+			} else {
+				msgs = append(msgs, fmt.Sprintf("    abi: clean (%d varied inputs)", result.Matches))
+			}
+		} else {
+			args := make([]byte, fl.Args)
+			_, report, err := k.CallFuncChecked(name, args)
+			if err != nil {
+				msgs = append(msgs, fmt.Sprintf("    abi: FAIL — %v", err))
+				failed = true
+			} else if !report.OK() {
+				msgs = append(msgs, fmt.Sprintf("    abi: %s", report))
+				failed = true
+			} else {
+				msgs = append(msgs, "    abi: clean")
+			}
+		}
+	}
+	return msgs, failed
+}
+
 // cmdVerifyCall implements `gasm verify --call <func> [--buf spec] [--repeat n]`.
 // It invokes a single function with user-supplied buffers and prints the arg
 // block before and after the call, so the user can inspect return values and

cmd/gasm/main_test.go

@@ -7,8 +7,11 @@ import (
 	"bytes"
 	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
+	"syscall"
 	"testing"
 )
 
@@ -237,3 +240,55 @@ func TestCmdArgErrors(t *testing.T) {
 		t.Errorf("cmdParse() code = %d, want 2", code)
 	}
 }
+
+// TestVerifySmokeCrashIsolation checks that a function faulting on its
+// zeroed smoke arguments is reported as CRASH by a child process instead of
+// killing `gasm verify` itself.
+func TestVerifySmokeCrashIsolation(t *testing.T) {
+	if testing.Short() {
+		t.Skip("builds the gasm binary")
+	}
+	if runtime.GOARCH != "amd64" {
+		t.Skip("amd64 JIT only")
+	}
+	bin := filepath.Join(t.TempDir(), "gasm")
+	if out, err := exec.Command("go", "build", "-o", bin, ".").CombinedOutput(); err != nil {
+		t.Fatalf("build gasm: %v\n%s", err, out)
+	}
+	src := filepath.Join(t.TempDir(), "crash_amd64.s")
+	kernel := "#include \"textflag.h\"\n" +
+		"\n" +
+		"// func Fault(x []byte) int\n" +
+		"TEXT ·Fault(SB), NOSPLIT, $0-32\n" +
+		"\tMOVQ\tx+0(FP), AX\n" +
+		"\tMOVQ\t(AX), AX // faults on the zeroed nil pointer\n" +
+		"\tMOVQ\tAX, ret+24(FP)\n" +
+		"\tRET\n"
+	if err := os.WriteFile(src, []byte(kernel), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	cmd := exec.Command(bin, "verify", "-smoke", src)
+	out, err := cmd.CombinedOutput()
+	if err == nil {
+		t.Fatalf("expected a failure report, got success:\n%s", out)
+	}
+	if exitErr, ok := err.(*exec.ExitError); ok {
+		if ws, ok := exitErr.Sys().(syscall.WaitStatus); ok && ws.Signaled() {
+			t.Fatalf("verify died from %v — the crash was not isolated:\n%s", ws.Signal(), out)
+		}
+	}
+	if !strings.Contains(string(out), "CRASH") {
+		t.Errorf("output does not report CRASH:\n%s", out)
+	}
+}
+
+func TestSweepCheckLines(t *testing.T) {
+	out := []byte("crash_amd64.s: 1 functions JIT-loaded\n" +
+		"  Fault: 21 bytes, args=32, frame=0 NOSPLIT\n" +
+		"    smoke: OK\n" +
+		"    abi: clean (10 varied inputs)\n")
+	want := "    smoke: OK\n    abi: clean (10 varied inputs)"
+	if got := sweepCheckLines(out); got != want {
+		t.Errorf("sweepCheckLines = %q, want %q", got, want)
+	}
+}