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

Author: gchatelet

libc/fuzzing/string/CMakeLists.txt

@@ -24,3 +24,19 @@ add_libc_fuzzer(
     libc.src.string.strstr
     libc.src.string.strlen
 )
+
+add_libc_fuzzer(
+  memcmp_fuzz
+  SRCS
+    memcmp_fuzz.cpp
+  DEPENDS
+    libc.src.string.memcmp
+)
+
+add_libc_fuzzer(
+  bcmp_fuzz
+  SRCS
+    bcmp_fuzz.cpp
+  DEPENDS
+    libc.src.string.bcmp
+)

libc/fuzzing/string/bcmp_fuzz.cpp

@@ -0,0 +1,54 @@
+//===-- bcmp_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 bcmp implementation.
+///
+//===----------------------------------------------------------------------===//
+#include "src/string/bcmp.h"
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int reference_bcmp(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;
+  return 0;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  const auto normalize = [](int value) -> int {
+    if (value == 0)
+      return 0;
+    return 1;
+  };
+  // We ignore the last byte is size is odd.
+  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::bcmp(a, b, count);
+  const int reference = reference_bcmp(a, b, count);
+  if (normalize(actual) == normalize(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");
+  };
+  printf("count    : %zu\n", count);
+  print("a        : ", a, count);
+  print("b        : ", b, count);
+  printf("expected : %d\n", reference);
+  printf("actual   : %d\n", actual);
+  __builtin_trap();
+}

libc/fuzzing/string/memcmp_fuzz.cpp

@@ -0,0 +1,59 @@
+//===-- 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;
+  };
+  // We ignore the last byte is size is odd.
+  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");
+  };
+  printf("count    : %zu\n", count);
+  print("a        : ", a, count);
+  print("b        : ", b, count);
+  printf("expected : %d\n", reference);
+  printf("actual   : %d\n", actual);
+  __builtin_trap();
+}