[libc] Add an implementation of qsort.

A fuzzer for qsort has also been added.

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D110382

2 files changed, 54 insertions, 0 deletions

diff --git a/libc/fuzzing/stdlib/CMakeLists.txt b/libc/fuzzing/stdlib/CMakeLists.txt
new file mode 100644
index 000000000000..db827f57075f
--- /dev/null
+++ b/libc/fuzzing/stdlib/CMakeLists.txt
@@ -0,0 +1,8 @@
+add_libc_fuzzer(
+  qsort_fuzz
+  SRCS
+    qsort_fuzz.cpp
+  DEPENDS
+    libc.src.stdlib.qsort
+)
+
diff --git a/libc/fuzzing/stdlib/qsort_fuzz.cpp b/libc/fuzzing/stdlib/qsort_fuzz.cpp
new file mode 100644
index 000000000000..dbbc8e96f924
--- /dev/null
+++ b/libc/fuzzing/stdlib/qsort_fuzz.cpp
@@ -0,0 +1,46 @@
+//===-- qsort_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 qsort implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/qsort.h"
+#include <stdint.h>
+
+static int int_compare(const void *l, const void *r) {
+  int li = *reinterpret_cast<const int *>(l);
+  int ri = *reinterpret_cast<const int *>(r);
+  if (li == ri)
+    return 0;
+  else if (li > ri)
+    return 1;
+  else
+    return -1;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  const size_t array_size = size / sizeof(int);
+  if (array_size == 0)
+    return 0;
+
+  int *array = new int[array_size];
+  const int *data_as_int = reinterpret_cast<const int *>(data);
+  for (size_t i = 0; i < array_size; ++i)
+    array[i] = data_as_int[i];
+
+  __llvm_libc::qsort(array, array_size, sizeof(int), int_compare);
+
+  for (size_t i = 0; i < array_size - 1; ++i) {
+    if (array[i] > array[i + 1])
+      __builtin_trap();
+  }
+
+  delete[] array;
+  return 0;
+}