[libc] Add the implementation of the GNU extension function fopencookie.

Reviewed By: lntue, michaelrj

Differential Revision: https://reviews.llvm.org/D124141

13 files changed, 420 insertions, 4 deletions

diff --git a/libc/config/linux/api.td b/libc/config/linux/api.td
index ed2b3b6b4ece..5d65a3c58a64 100644
--- a/libc/config/linux/api.td
+++ b/libc/config/linux/api.td
@@ -146,7 +146,7 @@ def StringAPI : PublicAPI<"string.h"> {
 }
 
 def StdIOAPI : PublicAPI<"stdio.h"> {
-  let Types = ["size_t", "FILE"];
+  let Types = ["size_t", "FILE", "cookie_io_functions_t"];
 }
 
 def StdlibAPI : PublicAPI<"stdlib.h"> {
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 5803468acf00..c007da837640 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -255,6 +255,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.stdio.flockfile
     libc.src.stdio.fflush
     libc.src.stdio.fopen
+    libc.src.stdio.fopencookie
     libc.src.stdio.fread
     libc.src.stdio.fread_unlocked
     libc.src.stdio.fseek
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index 9a4a888bd2d7..d011d6d6f59b 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -125,6 +125,7 @@ add_gen_header(
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.file_seek_macros
+    .llvm-libc-types.cookie_io_functions_t
     .llvm-libc-types.FILE
     .llvm-libc-types.size_t
 )
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index 9ddeeb73f499..3a5c17f4e29c 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -5,6 +5,7 @@ add_header(__mutex_type HDR __mutex_type.h)
 add_header(__qsortcompare_t HDR __qsortcompare_t.h)
 add_header(__sighandler_t HDR __sighandler_t.h)
 add_header(cnd_t HDR cnd_t.h)
+add_header(cookie_io_functions_t HDR cookie_io_functions_t.h DEPENDS .off64_t)
 add_header(double_t HDR double_t.h)
 add_header(div_t HDR div_t.h)
 add_header(ldiv_t HDR ldiv_t.h)
@@ -17,6 +18,7 @@ add_header(imaxdiv_t HDR imaxdiv_t.h)
 add_header(mode_t HDR mode_t.h)
 add_header(mtx_t HDR mtx_t.h DEPENDS .__futex_word .__mutex_type)
 add_header(off_t HDR off_t.h)
+add_header(off64_t HDR off64_t.h)
 add_header(once_flag HDR once_flag.h DEPENDS .__futex_word)
 add_header(pthread_attr_t HDR pthread_attr_t.h)
 add_header(pthread_mutexattr_t HDR pthread_mutexattr_t.h)
diff --git a/libc/include/llvm-libc-types/cookie_io_functions_t.h b/libc/include/llvm-libc-types/cookie_io_functions_t.h
new file mode 100644
index 000000000000..df904162a897
--- /dev/null
+++ b/libc/include/llvm-libc-types/cookie_io_functions_t.h
@@ -0,0 +1,28 @@
+//===-- Definition of type cookie_io_functions_t --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_TYPES_COOKIE_IO_FUNCTIONS_T_H
+#define __LLVM_LIBC_TYPES_COOKIE_IO_FUNCTIONS_T_H
+
+#include <llvm-libc-types/off64_t.h>
+#include <llvm-libc-types/size_t.h>
+#include <llvm-libc-types/ssize_t.h>
+
+typedef ssize_t cookie_read_function_t(void *, char *, size_t);
+typedef ssize_t cookie_write_function_t(void *, const char *, size_t);
+typedef int cookie_seek_function_t(void *, off64_t *, int);
+typedef int cookie_close_function_t(void *);
+
+typedef struct {
+  cookie_read_function_t *read;
+  cookie_write_function_t *write;
+  cookie_seek_function_t *seek;
+  cookie_close_function_t *close;
+} cookie_io_functions_t;
+
+#endif // __LLVM_LIBC_TYPES_COOKIE_IO_FUNCTIONS_T_H
diff --git a/libc/include/llvm-libc-types/off64_t.h b/libc/include/llvm-libc-types/off64_t.h
new file mode 100644
index 000000000000..0f95caa19cca
--- /dev/null
+++ b/libc/include/llvm-libc-types/off64_t.h
@@ -0,0 +1,14 @@
+//===-- Definition of off64_t type ----------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_TYPES_OFF64_T_H__
+#define __LLVM_LIBC_TYPES_OFF64_T_H__
+
+typedef __INT64_TYPE__ off64_t;
+
+#endif // __LLVM_LIBC_TYPES_OFF64_T_H__
diff --git a/libc/spec/gnu_ext.td b/libc/spec/gnu_ext.td
index 14ede61beffd..7fe8af0c2c03 100644
--- a/libc/spec/gnu_ext.td
+++ b/libc/spec/gnu_ext.td
@@ -1,4 +1,5 @@
 def GnuExtensions : StandardSpec<"GNUExtensions"> {
+  NamedType CookieIOFunctionsT = NamedType<"cookie_io_functions_t">;
   HeaderSpec CType = HeaderSpec<
     "ctype.h",
     [], // Macros
@@ -68,10 +69,15 @@ def GnuExtensions : StandardSpec<"GNUExtensions"> {
   HeaderSpec StdIO = HeaderSpec<
       "stdio.h",
       [], // Macros
-      [], // Types
+      [CookieIOFunctionsT], // Types
       [], // Enumerations
       [
           FunctionSpec<
+              "fopencookie",
+              RetValSpec<FILEPtr>,
+              [ArgSpec<VoidPtr>, ArgSpec<ConstCharPtr>, ArgSpec<CookieIOFunctionsT>]
+          >,
+          FunctionSpec<
               "fread_unlocked",
               RetValSpec<SizeTType>,
               [ArgSpec<VoidRestrictedPtr>,
@@ -88,7 +94,7 @@ def GnuExtensions : StandardSpec<"GNUExtensions"> {
                ArgSpec<FILERestrictedPtr>]
           >,
       ]
-   >;
+  >;
 
   let Headers = [
     CType,
diff --git a/libc/spec/spec.td b/libc/spec/spec.td
index 198900788c50..fe5b2005650d 100644
--- a/libc/spec/spec.td
+++ b/libc/spec/spec.td
@@ -110,7 +110,6 @@ def FILERestrictedPtr : RestrictedPtrType<FILE>;
 //added because __assert_fail needs it.
 def UnsignedType : NamedType<"unsigned">;
 
-
 class Macro<string name> {
   string Name = name;
 }
diff --git a/libc/src/stdio/CMakeLists.txt b/libc/src/stdio/CMakeLists.txt
index 048e46b91db3..77897e5eedb2 100644
--- a/libc/src/stdio/CMakeLists.txt
+++ b/libc/src/stdio/CMakeLists.txt
@@ -119,3 +119,14 @@ add_entrypoint_object(
     libc.src.__support.File.file
     libc.src.__support.File.platform_file
 )
+
+add_entrypoint_object(
+  fopencookie
+  SRCS
+    fopencookie.cpp
+  HDRS
+    fopencookie.h
+  DEPENDS
+    libc.include.stdio
+    libc.src.__support.File.file
+)
diff --git a/libc/src/stdio/fopencookie.cpp b/libc/src/stdio/fopencookie.cpp
new file mode 100644
index 000000000000..64177ebeb8ab
--- /dev/null
+++ b/libc/src/stdio/fopencookie.cpp
@@ -0,0 +1,83 @@
+//===-- Implementation of fopencookie -------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/fopencookie.h"
+#include "src/__support/File/file.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+namespace __llvm_libc {
+
+namespace {
+
+class CookieFile : public __llvm_libc::File {
+public:
+  void *cookie;
+  cookie_io_functions_t ops;
+};
+
+size_t write_func(File *f, const void *data, size_t size) {
+  auto cookie_file = reinterpret_cast<CookieFile *>(f);
+  if (cookie_file->ops.write == nullptr)
+    return 0;
+  return cookie_file->ops.write(cookie_file->cookie,
+                                reinterpret_cast<const char *>(data), size);
+}
+
+size_t read_func(File *f, void *data, size_t size) {
+  auto cookie_file = reinterpret_cast<CookieFile *>(f);
+  if (cookie_file->ops.read == nullptr)
+    return 0;
+  return cookie_file->ops.read(cookie_file->cookie,
+                               reinterpret_cast<char *>(data), size);
+}
+
+int seek_func(File *f, long offset, int whence) {
+  auto cookie_file = reinterpret_cast<CookieFile *>(f);
+  if (cookie_file->ops.seek == nullptr) {
+    errno = EINVAL;
+    return -1;
+  }
+  off64_t offset64 = offset;
+  return cookie_file->ops.seek(cookie_file->cookie, &offset64, whence);
+}
+
+int close_func(File *f) {
+  auto cookie_file = reinterpret_cast<CookieFile *>(f);
+  if (cookie_file->ops.close == nullptr)
+    return 0;
+  return cookie_file->ops.close(cookie_file->cookie);
+}
+
+int flush_func(File *f) { return 0; }
+
+} // anonymous namespace
+
+LLVM_LIBC_FUNCTION(::FILE *, fopencookie,
+                   (void *cookie, const char *mode,
+                    cookie_io_functions_t ops)) {
+  auto modeflags = File::mode_flags(mode);
+  void *buffer = malloc(File::DEFAULT_BUFFER_SIZE);
+  auto *file = reinterpret_cast<CookieFile *>(malloc(sizeof(CookieFile)));
+  if (file == nullptr)
+    return nullptr;
+
+  File::init(file, &write_func, &read_func, &seek_func, &close_func,
+             &flush_func, buffer, File::DEFAULT_BUFFER_SIZE,
+             0,    // Default buffering style
+             true, // Owned buffer
+             modeflags);
+  file->cookie = cookie;
+  file->ops = ops;
+
+  return reinterpret_cast<::FILE *>(file);
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/stdio/fopencookie.h b/libc/src/stdio/fopencookie.h
new file mode 100644
index 000000000000..d78e5ac3317d
--- /dev/null
+++ b/libc/src/stdio/fopencookie.h
@@ -0,0 +1,21 @@
+//===-- Implementation header of fopencookie --------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_FOPENCOOKIE_H
+#define LLVM_LIBC_SRC_STDIO_FOPENCOOKIE_H
+
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+::FILE *fopencookie(void *cookie, const char *__restrict mode,
+                    cookie_io_functions_t desc);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_FOPENCOOKIE_H
diff --git a/libc/test/src/stdio/CMakeLists.txt b/libc/test/src/stdio/CMakeLists.txt
index b2e3813a74c7..30e996c70c8d 100644
--- a/libc/test/src/stdio/CMakeLists.txt
+++ b/libc/test/src/stdio/CMakeLists.txt
@@ -30,6 +30,28 @@ add_libc_unittest(
     libc.src.stdio.fwrite_unlocked
 )
 
+add_libc_unittest(
+  fopencookie_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    fopencookie_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.stdio
+    libc.include.stdlib
+    libc.src.stdio.fclose
+    libc.src.stdio.fflush
+    libc.src.stdio.fopencookie
+    libc.src.stdio.fread
+    libc.src.stdio.fseek
+    libc.src.stdio.fwrite
+)
+
+target_link_libraries(
+  libc.test.src.stdio.fopencookie_test PRIVATE LibcMemoryHelpers
+)
+
 add_subdirectory(printf_core)
 
 add_subdirectory(testdata)
diff --git a/libc/test/src/stdio/fopencookie_test.cpp b/libc/test/src/stdio/fopencookie_test.cpp
new file mode 100644
index 000000000000..1445c9e1100a
--- /dev/null
+++ b/libc/test/src/stdio/fopencookie_test.cpp
@@ -0,0 +1,228 @@
+//===-- Unittests for the fopencookie function ----------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/fclose.h"
+#include "src/stdio/fflush.h"
+#include "src/stdio/fopencookie.h"
+#include "src/stdio/fread.h"
+#include "src/stdio/fseek.h"
+#include "src/stdio/fwrite.h"
+#include "utils/UnitTest/MemoryMatcher.h"
+#include "utils/UnitTest/Test.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+using MemoryView = __llvm_libc::memory::testing::MemoryView;
+
+struct StringStream {
+  char *buf;
+  size_t bufsize; // Size of buf
+  size_t endpos;  // 1 more than current fill size
+  size_t offset;  // Current read/write location
+};
+
+ssize_t write_ss(void *cookie, const char *buf, size_t size) {
+  auto *ss = reinterpret_cast<StringStream *>(cookie);
+  if (ss->offset + size > ss->bufsize)
+    ss->buf =
+        reinterpret_cast<char *>(realloc(ss->buf, (ss->offset + size) * 2));
+  for (size_t i = 0; i < size; ++i, ss->offset += 1)
+    ss->buf[ss->offset] = buf[i];
+  if (ss->offset > ss->endpos)
+    ss->endpos = ss->offset;
+  return size;
+}
+
+ssize_t read_ss(void *cookie, char *buf, size_t size) {
+  auto *ss = reinterpret_cast<StringStream *>(cookie);
+  ssize_t copysize = size;
+  if (ss->offset + size > ss->endpos) {
+    // You cannot copy more than what you have available.
+    copysize = ss->endpos - ss->offset;
+    if (copysize < 0)
+      copysize = 0; // A seek could have moved offset past the endpos
+  }
+  for (size_t i = 0; i < size_t(copysize); ++i, ++ss->offset)
+    buf[i] = ss->buf[ss->offset];
+  return copysize;
+}
+
+int seek_ss(void *cookie, off64_t *offset, int whence) {
+  auto *ss = reinterpret_cast<StringStream *>(cookie);
+  off64_t new_offset;
+  if (whence == SEEK_SET) {
+    new_offset = *offset;
+  } else if (whence == SEEK_CUR) {
+    new_offset = *offset + ss->offset;
+  } else if (whence == SEEK_END) {
+    new_offset = *offset + ss->endpos;
+  } else {
+    errno = EINVAL;
+    return -1;
+  }
+  if (new_offset < 0 || size_t(new_offset) > ss->bufsize)
+    return -1;
+  ss->offset = new_offset;
+  *offset = new_offset;
+  return 0;
+}
+
+int close_ss(void *cookie) {
+  auto *ss = reinterpret_cast<StringStream *>(cookie);
+  free(ss->buf);
+  ss->buf = nullptr;
+  ss->bufsize = ss->endpos = ss->offset = 0;
+  return 0;
+}
+
+constexpr cookie_io_functions_t STRING_STREAM_FUNCS = {&read_ss, &write_ss,
+                                                       &seek_ss, &close_ss};
+
+TEST(LlvmLibcFOpenCookie, ReadOnlyCookieTest) {
+  constexpr char CONTENT[] = "Hello,readonly!";
+  auto *ss = reinterpret_cast<StringStream *>(malloc(sizeof(StringStream)));
+  ss->buf = reinterpret_cast<char *>(malloc(sizeof(CONTENT)));
+  ss->bufsize = sizeof(CONTENT);
+  ss->offset = 0;
+  ss->endpos = ss->bufsize;
+  for (size_t i = 0; i < sizeof(CONTENT); ++i)
+    ss->buf[i] = CONTENT[i];
+
+  ::FILE *f = __llvm_libc::fopencookie(ss, "r", STRING_STREAM_FUNCS);
+  ASSERT_TRUE(f != nullptr);
+  char read_data[sizeof(CONTENT)];
+  ASSERT_EQ(sizeof(CONTENT),
+            __llvm_libc::fread(read_data, 1, sizeof(CONTENT), f));
+  ASSERT_STREQ(read_data, CONTENT);
+
+  ASSERT_EQ(0, __llvm_libc::fseek(f, 0, SEEK_SET));
+  // Should be an error to write.
+  ASSERT_EQ(size_t(0), __llvm_libc::fwrite(CONTENT, 1, sizeof(CONTENT), f));
+  ASSERT_EQ(errno, EBADF);
+  errno = 0;
+
+  ASSERT_EQ(0, __llvm_libc::fclose(f));
+  free(ss);
+}
+
+TEST(LlvmLibcFOpenCookie, WriteOnlyCookieTest) {
+  size_t INIT_BUFSIZE = 32;
+  auto *ss = reinterpret_cast<StringStream *>(malloc(sizeof(StringStream)));
+  ss->buf = reinterpret_cast<char *>(malloc(INIT_BUFSIZE));
+  ss->bufsize = INIT_BUFSIZE;
+  ss->offset = 0;
+  ss->endpos = 0;
+
+  ::FILE *f = __llvm_libc::fopencookie(ss, "w", STRING_STREAM_FUNCS);
+  ASSERT_TRUE(f != nullptr);
+
+  constexpr char WRITE_DATA[] = "Hello,writeonly!";
+  ASSERT_EQ(sizeof(WRITE_DATA),
+            __llvm_libc::fwrite(WRITE_DATA, 1, sizeof(WRITE_DATA), f));
+  // Flushing will ensure the data to be written to the string stream.
+  ASSERT_EQ(0, __llvm_libc::fflush(f));
+  ASSERT_STREQ(WRITE_DATA, ss->buf);
+
+  ASSERT_EQ(0, __llvm_libc::fseek(f, 0, SEEK_SET));
+  char read_data[sizeof(WRITE_DATA)];
+  // Should be an error to read.
+  ASSERT_EQ(size_t(0), __llvm_libc::fread(read_data, 1, sizeof(WRITE_DATA), f));
+  ASSERT_EQ(errno, EBADF);
+  errno = 0;
+
+  ASSERT_EQ(0, __llvm_libc::fclose(f));
+  free(ss);
+}
+
+TEST(LlvmLibcFOpenCookie, AppendOnlyCookieTest) {
+  constexpr char INITIAL_CONTENT[] = "1234567890987654321";
+  constexpr char WRITE_DATA[] = "append";
+  auto *ss = reinterpret_cast<StringStream *>(malloc(sizeof(StringStream)));
+  ss->buf = reinterpret_cast<char *>(malloc(sizeof(INITIAL_CONTENT)));
+  ss->bufsize = sizeof(INITIAL_CONTENT);
+  ss->offset = ss->bufsize; // We want to open the file in append mode.
+  ss->endpos = ss->bufsize;
+  for (size_t i = 0; i < sizeof(INITIAL_CONTENT); ++i)
+    ss->buf[i] = INITIAL_CONTENT[i];
+
+  ::FILE *f = __llvm_libc::fopencookie(ss, "a", STRING_STREAM_FUNCS);
+  ASSERT_TRUE(f != nullptr);
+
+  constexpr size_t READ_SIZE = 5;
+  char read_data[READ_SIZE];
+  // This is not a readable file.
+  ASSERT_EQ(__llvm_libc::fread(read_data, 1, READ_SIZE, f), size_t(0));
+  EXPECT_NE(errno, 0);
+  errno = 0;
+
+  ASSERT_EQ(__llvm_libc::fwrite(WRITE_DATA, 1, sizeof(WRITE_DATA), f),
+            sizeof(WRITE_DATA));
+  EXPECT_EQ(__llvm_libc::fflush(f), 0);
+  EXPECT_EQ(ss->endpos, sizeof(WRITE_DATA) + sizeof(INITIAL_CONTENT));
+
+  ASSERT_EQ(__llvm_libc::fclose(f), 0);
+  free(ss);
+}
+
+TEST(LlvmLibcFOpenCookie, ReadUpdateCookieTest) {
+  const char INITIAL_CONTENT[] = "1234567890987654321";
+  auto *ss = reinterpret_cast<StringStream *>(malloc(sizeof(StringStream)));
+  ss->buf = reinterpret_cast<char *>(malloc(sizeof(INITIAL_CONTENT)));
+  ss->bufsize = sizeof(INITIAL_CONTENT);
+  ss->offset = 0;
+  ss->endpos = ss->bufsize;
+  for (size_t i = 0; i < sizeof(INITIAL_CONTENT); ++i)
+    ss->buf[i] = INITIAL_CONTENT[i];
+
+  ::FILE *f = __llvm_libc::fopencookie(ss, "r+", STRING_STREAM_FUNCS);
+  ASSERT_TRUE(f != nullptr);
+
+  constexpr size_t READ_SIZE = sizeof(INITIAL_CONTENT) / 2;
+  char read_data[READ_SIZE];
+  ASSERT_EQ(READ_SIZE, __llvm_libc::fread(read_data, 1, READ_SIZE, f));
+
+  MemoryView src1(INITIAL_CONTENT, READ_SIZE), dst1(read_data, READ_SIZE);
+  EXPECT_MEM_EQ(src1, dst1);
+
+  ASSERT_EQ(__llvm_libc::fseek(f, 0, SEEK_SET), 0);
+  constexpr char WRITE_DATA[] = "hello, file";
+  ASSERT_EQ(sizeof(WRITE_DATA),
+            __llvm_libc::fwrite(WRITE_DATA, 1, sizeof(WRITE_DATA), f));
+  ASSERT_EQ(__llvm_libc::fflush(f), 0);
+  EXPECT_STREQ(ss->buf, WRITE_DATA);
+
+  ASSERT_EQ(__llvm_libc::fclose(f), 0);
+  free(ss);
+}
+
+TEST(LlvmLibcFOpenCookie, WriteUpdateCookieTest) {
+  constexpr char WRITE_DATA[] = "hello, file";
+  auto *ss = reinterpret_cast<StringStream *>(malloc(sizeof(StringStream)));
+  ss->buf = reinterpret_cast<char *>(malloc(sizeof(WRITE_DATA)));
+  ss->bufsize = sizeof(WRITE_DATA);
+  ss->offset = 0;
+  ss->endpos = 0;
+
+  ::FILE *f = __llvm_libc::fopencookie(ss, "w+", STRING_STREAM_FUNCS);
+  ASSERT_TRUE(f != nullptr);
+
+  ASSERT_EQ(sizeof(WRITE_DATA),
+            __llvm_libc::fwrite(WRITE_DATA, 1, sizeof(WRITE_DATA), f));
+
+  ASSERT_EQ(__llvm_libc::fseek(f, 0, SEEK_SET), 0);
+
+  char read_data[sizeof(WRITE_DATA)];
+  ASSERT_EQ(__llvm_libc::fread(read_data, 1, sizeof(read_data), f),
+            sizeof(read_data));
+  EXPECT_STREQ(read_data, WRITE_DATA);
+
+  ASSERT_EQ(__llvm_libc::fclose(f), 0);
+  free(ss);
+}