2 files changed, 63 insertions, 0 deletions
diff --git a/libc/fuzzing/string/CMakeLists.txt b/libc/fuzzing/string/CMakeLists.txt
index 326bf9c07175..db3def324fcc 100644
--- a/libc/fuzzing/string/CMakeLists.txt
+++ b/libc/fuzzing/string/CMakeLists.txt
@@ -7,3 +7,11 @@ add_libc_fuzzer(
     libc.src.string.strcpy
     libc.src.string.strlen
 )
+
+add_libc_fuzzer(
+  strcmp_fuzz
+  SRCS
+    strcmp_fuzz.cpp
+  DEPENDS
+    libc.src.string.strcmp
+)
diff --git a/libc/fuzzing/string/strcmp_fuzz.cpp b/libc/fuzzing/string/strcmp_fuzz.cpp
new file mode 100644
index 000000000000..14c6e4d10e71
--- /dev/null
+++ b/libc/fuzzing/string/strcmp_fuzz.cpp
@@ -0,0 +1,55 @@
+//===-- strcmp_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 strcmp implementation.
+///
+//===----------------------------------------------------------------------===//
+#include "src/string/strcmp.h"
+#include <algorithm>
+#include <stdint.h>
+
+extern "C" int LLVMFuzzerTestTwoInputs(const uint8_t *data1, size_t size1,
+                                       const uint8_t *data2, size_t size2) {
+  // Verify each data source contains at least one character.
+  if (!size1 || !size2)
+    return 0;
+  // Verify that the final character is the null terminator.
+  if (data1[size1 - 1] != '\0' || data2[size2 - 1] != '\0')
+    return 0;
+
+  const char *s1 = reinterpret_cast<const char *>(data1);
+  const char *s2 = reinterpret_cast<const char *>(data2);
+
+  const size_t minimum_size = std::min(size1, size2);
+
+  // Iterate through until either the minimum size is hit,
+  // a character is the null terminator, or the first set
+  // of differed bytes between s1 and s2 are found.
+  // No bytes following a null byte should be compared.
+  size_t i;
+  for (i = 0; i < minimum_size && s1[i] && s1[i] == s2[i]; ++i)
+    ;
+
+  int expected_result = s1[i] - s2[i];
+  int actual_result = __llvm_libc::strcmp(s1, s2);
+
+  // The expected result should be the difference between the first non-equal
+  // characters of s1 and s2. If all characters are equal, the expected result
+  // should be '\0' - '\0' = 0.
+  if (expected_result != actual_result)
+    __builtin_trap();
+
+  // Verify reversed operands. This should be the negated value of the previous
+  // result, except of course if the previous result was zero.
+  expected_result = s2[i] - s1[i];
+  actual_result = __llvm_libc::strcmp(s2, s1);
+  if (expected_result != actual_result)
+    __builtin_trap();
+
+  return 0;
+}