feat(verify): combine ABI checks with fuzzing for deep-path testing

cmd/gasm/main.go

@@ -633,6 +633,7 @@ With -profile, the static basic-block structure is listed for each function.
 `)
 	smoke := fs.Bool("smoke", false, "call each NOSPLIT function with zeroed args")
 	abi := fs.Bool("abi", false, "run ABI-checking calls (sentinel registers + red zone)")
+	abiN := fs.Int("abi-n", 100, "number of ABI check iterations with varied inputs")
 	profile := fs.Bool("profile", false, "list basic-block structure per function")
 	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")
@@ -823,16 +824,28 @@ With -profile, the static basic-block structure is listed for each function.
 		}
 
 		if *abi && fl.NoSplit {
-			args := make([]byte, fl.Args)
-			_, report, err := k.CallFuncChecked(name, args)
-			if err != nil {
-				fmt.Printf("    abi: FAIL — %v\n", err)
-				rc = 1
-			} else if !report.OK() {
-				fmt.Printf("    abi: %s\n", report)
-				rc = 1
+			// Try varied-input ABI fuzzing first.
+			if src, err := readSource(path); err == nil {
+				result := k.FuzzFuncCheckedByName(name, src, *abiN, int64(*abiN))
+				if result.Mismatches > 0 {
+					fmt.Printf("    abi: %s\n", result)
+					rc = 1
+				} else {
+					fmt.Printf("    abi: clean (%d varied inputs)\n", result.Matches)
+				}
 			} else {
-				fmt.Printf("    abi: clean\n")
+				// Fallback: single zeroed-arg call.
+				args := make([]byte, fl.Args)
+				_, report, err := k.CallFuncChecked(name, args)
+				if err != nil {
+					fmt.Printf("    abi: FAIL — %v\n", err)
+					rc = 1
+				} else if !report.OK() {
+					fmt.Printf("    abi: %s\n", report)
+					rc = 1
+				} else {
+					fmt.Printf("    abi: clean\n")
+				}
 			}
 		}
 	}

verify/verify.go

@@ -5,6 +5,7 @@ package verify
 
 import (
 	"fmt"
+	"math/rand"
 	"os"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
@@ -114,6 +115,66 @@ func (k *Kernel) CallFuncChecked(name string, args []byte) ([]byte, ABIReport, e
 	return CallChecked(fnAddr, args)
 }
 
+// FuzzFuncCheckedByName is like FuzzFuncChecked but extracts the signature
+// from the source code internally.
+func (k *Kernel) FuzzFuncCheckedByName(name, src string, iterations int, seed int64) FuzzResult {
+	result := FuzzResult{Func: name, Iterations: iterations}
+	sig, ok := ExtractSignatures(src)[name]
+	if !ok {
+		result.Mismatches = iterations
+		result.FirstFail = "no // func signature found"
+		return result
+	}
+	return k.FuzzFuncChecked(name, sig, iterations, seed)
+}
+
+// FuzzFuncChecked combines fuzzing with ABI checks: it generates varied
+// inputs and verifies that callee-saved registers and the red zone are
+// preserved even on deep execution paths (not just early exits).
+func (k *Kernel) FuzzFuncChecked(name string, sig funcSig, iterations int, seed int64) FuzzResult {
+	result := FuzzResult{Func: name, Iterations: iterations}
+	rng := rand.New(rand.NewSource(seed))
+
+	fl, err := k.Func(name)
+	if err != nil {
+		result.Mismatches = iterations
+		result.FirstFail = err.Error()
+		return result
+	}
+
+	violations := 0
+	for i := 0; i < iterations; i++ {
+		gasmArgs, _, bufs := genDualArgs(rng, sig, fl.Args)
+		result.CrashInput = gasmArgs
+
+		_, report, err := k.CallFuncChecked(name, gasmArgs)
+		if err != nil {
+			result.Mismatches++
+			if result.FirstFail == "" {
+				result.FirstFail = fmt.Sprintf("iter %d: call: %v", i, err)
+			}
+			releaseBufs(bufs)
+			continue
+		}
+
+		if !report.OK() {
+			violations++
+			result.Mismatches++
+			if result.FirstFail == "" {
+				result.FirstFail = fmt.Sprintf("iter %d: %s", i, report.String())
+			}
+		} else {
+			result.Matches++
+		}
+		releaseBufs(bufs)
+	}
+
+	if violations > 0 && result.FirstFail == "" {
+		result.FirstFail = fmt.Sprintf("%d ABI violations across %d iterations", violations, iterations)
+	}
+	return result
+}
+
 // Close releases the executable mapping.
 func (k *Kernel) Close() {
 	if k.exec != nil {