feat(cgo): validate Int conversion against C.int width

Co-Authored-By: Virgil <virgil@lethean.io>

call_test.go

@@ -21,6 +21,38 @@ func TestSizeTAndIntConversions(t *testing.T) {
 	if got := Int(4096); got != 4096 {
 		t.Fatalf("expected Int(4096) to be 4096, got %v", got)
 	}
+
+	cIntBits := cIntBitSize()
+	maxInt := int64(int(^uint(0) >> 1))
+	minInt := -maxInt - 1
+	cIntMax := int64(1)<<(cIntBits-1) - 1
+	cIntMin := -cIntMax - 1
+
+	// Verify exact C.int boundaries for this platform.
+	if cIntMax <= maxInt {
+		got := Int(int(cIntMax))
+		if int(got) != int(cIntMax) {
+			t.Fatalf("expected Int(%d) to be %d, got %v", cIntMax, cIntMax, got)
+		}
+	}
+	if cIntMin >= minInt {
+		got := Int(int(cIntMin))
+		if int(got) != int(cIntMin) {
+			t.Fatalf("expected Int(%d) to be %d, got %v", cIntMin, cIntMin, got)
+		}
+	}
+
+	// Int should panic when value is outside C.int range.
+	if cIntMax < maxInt {
+		assertPanics(t, "value exceeds C.int range", func() {
+			_ = Int(int(cIntMax + 1))
+		})
+	}
+	if cIntMin > minInt {
+		assertPanics(t, "value exceeds C.int range", func() {
+			_ = Int(int(cIntMin - 1))
+		})
+	}
 }
 
 func TestCallWrapsZeroAndNonZeroReturns(t *testing.T) {

string_conversion.go

@@ -73,12 +73,22 @@ func SizeT(value int) C.size_t {
 //
 //	rc := cgo.Int(returnCode)
 func Int(value int) C.int {
-	if value < -2147483648 || value > 2147483647 {
-		panic("cgo.Int: value exceeds C.int range")
+	cIntBits := cIntBitSize()
+	if cIntBits < strconv.IntSize {
+		maxValue := (int64(1) << (cIntBits - 1)) - 1
+		minValue := -maxValue - 1
+		casted := int64(value)
+		if casted < minValue || casted > maxValue {
+			panic("cgo.Int: value exceeds C.int range")
+		}
 	}
 	return C.int(value)
 }
 
+func cIntBitSize() int {
+	return int(unsafe.Sizeof(C.int(0)) * 8)
+}
+
 // Call invokes a C function pointer and maps a non-zero return into a Go error.
 //
 //	err := cgo.Call(unsafe.Pointer(C.some_function), cgo.SizeT(len(data)))