[libc-commits] [libc] [libc] Add memcmp / bcmp fuzzers (PR #77741)

[Clement Courbet via libc-commits]

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@@ -0,0 +1,57 @@
+//===-- memcmp_fuzz.cpp ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc memcmp implementation.
+///
+//===----------------------------------------------------------------------===//
+#include "src/string/memcmp.h"
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int reference_memcmp(const void *pa, const void *pb, size_t count)
+    __attribute__((no_builtin)) {
+  const auto *a = reinterpret_cast<const unsigned char *>(pa);
+  const auto *b = reinterpret_cast<const unsigned char *>(pb);
+  for (size_t i = 0; i < count; ++i, ++a, ++b) {
+    if (*a < *b)
+      return -1;
+    else if (*a > *b)
+      return 1;
+  }
+  return 0;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  const auto sign = [](int value) -> int {
+    if (value < 0)
+      return -1;
+    if (value > 0)
+      return 1;
+    return 0;
+  };
+  const auto count = size / 2;
+  const char *a = reinterpret_cast<const char *>(data);
+  const char *b = reinterpret_cast<const char *>(data) + count;
+  const int actual = LIBC_NAMESPACE::memcmp(a, b, count);
+  const int reference = reference_memcmp(a, b, count);
+  if (sign(actual) == sign(reference))
+    return 0;
+  const auto print = [](const char *msg, const char *buffer, size_t size) {
+    printf("%s\"", msg);
+    for (size_t i = 0; i < size; ++i)
+      printf("\\x%02x", (uint8_t)buffer[i]);
+    printf("\"\n");
+  };
+  print("a     : ", a, count);
+  print("b     : ", b, count);
+  printf("count : %zu\n", count);
+  printf("result: %d\n", reference);
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legrosbuffle wrote:

You probably want to print the actual result too, given that there are 3 semantically distinct values.

https://github.com/llvm/llvm-project/pull/77741