diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -45,6 +45,15 @@
     libc.src.__support.CPP.expected
 )
 
+add_header_library(
+  c_string
+  HDRS
+    c_string.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.CPP.string
+)
+
 add_header_library(
   ctype_utils
   HDRS
diff --git a/libc/src/__support/c_string.h b/libc/src/__support/c_string.h
new file mode 100644
--- /dev/null
+++ b/libc/src/__support/c_string.h
@@ -0,0 +1,36 @@
+//===-- Implementation of a struct to hold a string in menory -------------===//
+//
+// 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_SUPPORT_C_STRING_H
+#define LLVM_LIBC_SRC_SUPPORT_C_STRING_H
+
+#include "src/__support/CPP/string.h"
+#include "src/__support/macros/attributes.h" // for LIBC_INLINE
+
+namespace __llvm_libc {
+
+// The CString class is a companion to the cpp::string class. Its use case is as
+// a return value for a function that in C would return a char* and a flag for
+// if that char* needs to be freed.
+class CString {
+  cpp::string str;
+
+public:
+  // These constructors can be implemented iff required.
+  CString() = delete;
+  CString(const CString &) = delete;
+  CString(CString &&) = delete;
+
+  LIBC_INLINE CString(cpp::string in_str) : str(in_str) {}
+
+  LIBC_INLINE operator const char *() const { return str.c_str(); }
+};
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_C_STRING_H
diff --git a/libc/src/stdio/fprintf.cpp b/libc/src/stdio/fprintf.cpp
--- a/libc/src/stdio/fprintf.cpp
+++ b/libc/src/stdio/fprintf.cpp
@@ -8,7 +8,6 @@
 
 #include "src/stdio/fprintf.h"
 
-#include "src/__support/File/file.h"
 #include "src/__support/arg_list.h"
 #include "src/stdio/printf_core/vfprintf_internal.h"
 
@@ -18,6 +17,7 @@
 namespace __llvm_libc {
 
 #ifndef LIBC_COPT_PRINTF_USE_SYSTEM_FILE
+#include "src/__support/File/file.h"
 using FileT = __llvm_libc::File;
 #else  // defined(LIBC_COPT_PRINTF_USE_SYSTEM_FILE)
 using FileT = ::FILE;
diff --git a/libc/test/UnitTest/BazelFilePath.cpp b/libc/test/UnitTest/BazelFilePath.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/UnitTest/BazelFilePath.cpp
@@ -0,0 +1,25 @@
+//===-- Implementation of the file path generator for bazel ---------------===//
+//
+// 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 "LibcTest.h"
+
+#include <stdlib.h>
+
+#include "src/__support/CPP/string.h"
+#include "src/__support/c_string.h"
+
+namespace __llvm_libc::testing {
+
+CString libc_make_test_file_path_func(const char *file_name) {
+  // This is the path to the folder bazel wants the test outputs written to.
+  const char *UNDECLARED_OUTPUTS_PATH = getenv("TEST_UNDECLARED_OUTPUTS_DIR");
+
+  return cpp::string(UNDECLARED_OUTPUTS_PATH) + file_name;
+}
+
+} // namespace __llvm_libc::testing
diff --git a/libc/test/UnitTest/CMakeLists.txt b/libc/test/UnitTest/CMakeLists.txt
--- a/libc/test/UnitTest/CMakeLists.txt
+++ b/libc/test/UnitTest/CMakeLists.txt
@@ -1,6 +1,7 @@
 set(libc_test_srcs_common
   Test.h
   LibcTest.cpp
+  CmakeFilePath.cpp
   LibcTest.h
   TestLogger.cpp
   TestLogger.h
@@ -29,6 +30,7 @@
   target_compile_options(${lib} PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS}
                          -fno-exceptions -fno-rtti)
   add_dependencies(${lib}
+    libc.src.__support.c_string
     libc.src.__support.CPP.string
     libc.src.__support.CPP.string_view
     libc.src.__support.CPP.type_traits
diff --git a/libc/test/UnitTest/CmakeFilePath.cpp b/libc/test/UnitTest/CmakeFilePath.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/UnitTest/CmakeFilePath.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of the file path generator for cmake ---------------===//
+//
+// 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 "LibcTest.h"
+
+#include "src/__support/CPP/string.h"
+#include "src/__support/c_string.h"
+
+namespace __llvm_libc::testing {
+
+CString libc_make_test_file_path_func(const char *file_name) {
+  return cpp::string(file_name);
+}
+
+} // namespace __llvm_libc::testing
diff --git a/libc/test/UnitTest/LibcTest.h b/libc/test/UnitTest/LibcTest.h
--- a/libc/test/UnitTest/LibcTest.h
+++ b/libc/test/UnitTest/LibcTest.h
@@ -9,14 +9,26 @@
 #ifndef LLVM_LIBC_UTILS_UNITTEST_LIBCTEST_H
 #define LLVM_LIBC_UTILS_UNITTEST_LIBCTEST_H
 
-// This file can only include headers from src/__support/CPP/ or
-// utils/testutils. No other headers should be included.
+// This is defined as a simple macro in test.h so that it exists for platforms
+// that don't use our test infrastructure. It's defined as a proper function
+// below.
+#ifdef libc_make_test_file_path
+#undef libc_make_test_file_path
+#endif // libc_make_test_file_path
+
+// This is defined as a macro here to avoid namespace issues.
+#define libc_make_test_file_path(file_name)                                    \
+  (__llvm_libc::testing::libc_make_test_file_path_func(file_name))
+
+// This file can only include headers from src/__support/ or test/UnitTest. No
+// other headers should be included.
 
 #include "PlatformDefs.h"
 
 #include "src/__support/CPP/string.h"
 #include "src/__support/CPP/string_view.h"
 #include "src/__support/CPP/type_traits.h"
+#include "src/__support/c_string.h"
 #include "test/UnitTest/ExecuteFunction.h"
 #include "test/UnitTest/TestLogger.h"
 
@@ -259,6 +271,8 @@
 // Make TypeList visible in __llvm_libc::testing.
 template <typename... Types> using TypeList = internal::TypeList<Types...>;
 
+CString libc_make_test_file_path_func(const char *file_name);
+
 } // namespace testing
 } // namespace __llvm_libc
 
diff --git a/libc/test/UnitTest/Test.h b/libc/test/UnitTest/Test.h
--- a/libc/test/UnitTest/Test.h
+++ b/libc/test/UnitTest/Test.h
@@ -9,6 +9,13 @@
 #ifndef LLVM_LIBC_UTILS_UNITTEST_TEST_H
 #define LLVM_LIBC_UTILS_UNITTEST_TEST_H
 
+// This macro takes a file name and returns a value implicitly castable to
+// a const char*. That const char* is the path to a file with the provided name
+// in a directory where the test is allowed to write. By default it writes
+// directly to the filename provided, but implementations are allowed to
+// redefine it as necessary.
+#define libc_make_test_file_path(file_name) (file_name)
+
 #ifdef LIBC_COPT_TEST_USE_FUCHSIA
 #include "FuchsiaTest.h"
 #elif defined(LIBC_COPT_TEST_USE_PIGWEED)
diff --git a/libc/test/src/stdio/fprintf_test.cpp b/libc/test/src/stdio/fprintf_test.cpp
--- a/libc/test/src/stdio/fprintf_test.cpp
+++ b/libc/test/src/stdio/fprintf_test.cpp
@@ -34,8 +34,10 @@
 } // namespace printf_test
 
 TEST(LlvmLibcFPrintfTest, WriteToFile) {
-  constexpr char FILENAME[] = "testdata/fprintf_output.test";
-  ::FILE *file = printf_test::fopen(FILENAME, "w");
+  const char *FILENAME = "fprintf_output.test";
+  auto FILE_PATH = libc_make_test_file_path(FILENAME);
+
+  ::FILE *file = printf_test::fopen(FILE_PATH, "w");
   ASSERT_FALSE(file == nullptr);
 
   int written;
@@ -55,7 +57,7 @@
 
   ASSERT_EQ(0, printf_test::fclose(file));
 
-  file = printf_test::fopen(FILENAME, "r");
+  file = printf_test::fopen(FILE_PATH, "r");
   ASSERT_FALSE(file == nullptr);
 
   char data[50];
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -20,6 +20,12 @@
 
 licenses(["notice"])
 
+PRINTF_COPTS = [
+    "LIBC_COPT_PRINTF_USE_SYSTEM_FILE",
+    "LIBC_COPT_PRINTF_DISABLE_INDEX_MODE",
+    "LIBC_COPT_PRINTF_DISABLE_WRITE_INT",
+]
+
 # A flag to pick which `mpfr` to use for math tests.
 # Usage: `--@llvm-project//libc:mpfr=<disable|external|system>`.
 # Flag documentation: https://bazel.build/extending/config
@@ -153,6 +159,14 @@
     ],
 )
 
+libc_support_library(
+    name = "__support_cpp_expected",
+    hdrs = ["src/__support/CPP/expected.h"],
+    deps = [
+        ":libc_root",
+    ],
+)
+
 libc_support_library(
     name = "__support_cpp_functional",
     hdrs = ["src/__support/CPP/functional.h"],
@@ -170,6 +184,16 @@
     deps = [":libc_root"],
 )
 
+libc_support_library(
+    name = "__support_cpp_new",
+    srcs = ["src/__support/CPP/new.cpp"],
+    hdrs = ["src/__support/CPP/new.h"],
+    deps = [
+        ":__support_common",
+        ":libc_root",
+    ],
+)
+
 libc_support_library(
     name = "__support_cpp_optional",
     hdrs = ["src/__support/CPP/optional.h"],
@@ -244,6 +268,25 @@
     ],
 )
 
+libc_support_library(
+    name = "__support_c_string",
+    hdrs = ["src/__support/c_string.h"],
+    deps = [
+        ":__support_cpp_string",
+        ":libc_root",
+    ],
+)
+
+libc_support_library(
+    name = "__support_error_or",
+    hdrs = ["src/__support/error_or.h"],
+    deps = [
+        ":__support_common",
+        ":__support_cpp_expected",
+        ":libc_root",
+    ],
+)
+
 libc_support_library(
     name = "__support_float_to_string",
     hdrs = [
@@ -398,6 +441,20 @@
     ],
 )
 
+libc_support_library(
+    name = "__support_file_file",
+    srcs = ["src/__support/File/file.cpp"],
+    hdrs = ["src/__support/File/file.h"],
+    deps = [
+        ":__support_cpp_new",
+        ":__support_cpp_span",
+        ":__support_error_or",
+        ":__support_threads_mutex",
+        ":errno",
+        ":libc_root",
+    ],
+)
+
 libc_support_library(
     name = "__support_named_pair",
     hdrs = ["src/__support/named_pair.h"],
@@ -701,6 +758,23 @@
     ],
 )
 
+libc_support_library(
+    name = "__support_threads_mutex",
+    hdrs = [
+        "src/__support/threads/mutex.h",
+        "src/__support/threads/mutex_common.h",
+    ],
+    textual_hdrs = [
+        "src/__support/threads/linux/mutex.h",
+        "src/__support/threads/linux/futex_word.h",
+    ],
+    deps = [
+        ":__support_cpp_atomic",
+        ":__support_osutil_syscall",
+        ":libc_root",
+    ],
+)
+
 ############################### errno targets ################################
 
 libc_function(
@@ -2080,6 +2154,7 @@
 libc_support_library(
     name = "printf_core_structs",
     hdrs = ["src/stdio/printf_core/core_structs.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_cpp_string_view",
         ":__support_fputil_fp_bits",
@@ -2090,6 +2165,7 @@
 libc_support_library(
     name = "printf_config",
     hdrs = ["src/stdio/printf_core/printf_config.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":libc_root",
     ],
@@ -2099,6 +2175,7 @@
     name = "printf_parser",
     srcs = ["src/stdio/printf_core/parser.cpp"],
     hdrs = ["src/stdio/printf_core/parser.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_arg_list",
         ":__support_common",
@@ -2120,7 +2197,7 @@
     name = "printf_mock_parser",
     srcs = ["src/stdio/printf_core/parser.cpp"],
     hdrs = ["src/stdio/printf_core/parser.h"],
-    copts = ["-DLIBC_COPT_MOCK_ARG_LIST"],
+    defines = PRINTF_COPTS + ["LIBC_COPT_MOCK_ARG_LIST"],
     deps = [
         ":__support_arg_list",
         ":__support_common",
@@ -2141,6 +2218,7 @@
     name = "printf_string_writer",
     srcs = ["src/stdio/printf_core/string_writer.cpp"],
     hdrs = ["src/stdio/printf_core/string_writer.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_cpp_string_view",
         ":libc_root",
@@ -2149,10 +2227,23 @@
     ],
 )
 
+libc_support_library(
+    name = "printf_file_writer",
+    hdrs = ["src/stdio/printf_core/file_writer.h"],
+    defines = PRINTF_COPTS,
+    deps = [
+        ":__support_cpp_string_view",
+        ":__support_file_file",
+        ":libc_root",
+        ":printf_core_structs",
+    ],
+)
+
 libc_support_library(
     name = "printf_writer",
     srcs = ["src/stdio/printf_core/writer.cpp"],
     hdrs = ["src/stdio/printf_core/writer.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_cpp_string_view",
         ":libc_root",
@@ -2175,6 +2266,7 @@
         "src/stdio/printf_core/string_converter.h",
         "src/stdio/printf_core/write_int_converter.h",
     ],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_common",
         ":__support_cpp_limits",
@@ -2197,6 +2289,7 @@
     name = "printf_main",
     srcs = ["src/stdio/printf_core/printf_main.cpp"],
     hdrs = ["src/stdio/printf_core/printf_main.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_arg_list",
         ":libc_root",
@@ -2211,6 +2304,7 @@
     name = "sprintf",
     srcs = ["src/stdio/sprintf.cpp"],
     hdrs = ["src/stdio/sprintf.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_arg_list",
         ":errno",
@@ -2224,6 +2318,7 @@
     name = "snprintf",
     srcs = ["src/stdio/snprintf.cpp"],
     hdrs = ["src/stdio/snprintf.h"],
+    defines = PRINTF_COPTS,
     deps = [
         ":__support_arg_list",
         ":errno",
@@ -2232,3 +2327,41 @@
         ":printf_writer",
     ],
 )
+
+libc_support_library(
+    name = "vfprintf_internal",
+    hdrs = ["src/stdio/printf_core/vfprintf_internal.h"],
+    defines = PRINTF_COPTS,
+    deps = [
+        ":__support_arg_list",
+        ":__support_file_file",
+        ":__support_macros_attributes",
+        ":printf_file_writer",
+        ":printf_main",
+        ":printf_writer",
+    ],
+)
+
+libc_function(
+    name = "printf",
+    srcs = ["src/stdio/printf.cpp"],
+    hdrs = ["src/stdio/printf.h"],
+    defines = PRINTF_COPTS,
+    deps = [
+        ":__support_arg_list",
+        ":errno",
+        ":vfprintf_internal",
+    ],
+)
+
+libc_function(
+    name = "fprintf",
+    srcs = ["src/stdio/fprintf.cpp"],
+    hdrs = ["src/stdio/fprintf.h"],
+    defines = PRINTF_COPTS,
+    deps = [
+        ":__support_arg_list",
+        ":errno",
+        ":vfprintf_internal",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
--- a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
+++ b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
@@ -23,7 +23,7 @@
     # We want all libc sources to be compiled with "hidden" visibility.
     # The public symbols will be given "default" visibility explicitly.
     # See src/__support/common.h for more information.
-    copts.append("-fvisibility=hidden")
+    copts = copts + ["-fvisibility=hidden"]
     native.cc_library(
         name = name,
         copts = copts,
@@ -65,11 +65,11 @@
       **kwargs: Other attributes relevant for a cc_library. For example, deps.
     """
     deps = deps or []
-    deps.append(LIBC_ROOT_TARGET)
+    # We use the explicit equals pattern here because append and += mutate the
+    # original list, where this creates a new list and stores it in deps.
+    deps = deps + [LIBC_ROOT_TARGET]
     copts = copts or []
-    copts.append("-O3")
-    copts.append("-fno-builtin")
-    copts.append("-fno-lax-vector-conversions")
+    copts = copts + ["-O3", "-fno-builtin", "-fno-lax-vector-conversions"]
 
     # We compile the code twice, the first target is suffixed with ".__internal__" and contains the
     # C++ functions in the "__llvm_libc" namespace. This allows us to test the function in the
@@ -87,9 +87,9 @@
 
     func_attrs = ["__attribute__((visibility(\"default\")))"]
     if weak:
-        func_attrs.append("__attribute__((weak))")
+        func_attrs = func_attrs + ["__attribute__((weak))"]
     local_defines = local_defines or ["LIBC_COPT_PUBLIC_PACKAGING"]
-    local_defines.append("LLVM_LIBC_FUNCTION_ATTR='%s'" % " ".join(func_attrs))
+    local_defines = local_defines + ["LLVM_LIBC_FUNCTION_ATTR='%s'" % " ".join(func_attrs)]
     _libc_library(
         name = name,
         srcs = srcs,
diff --git a/utils/bazel/llvm-project-overlay/libc/test/UnitTest/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/UnitTest/BUILD.bazel
--- a/utils/bazel/llvm-project-overlay/libc/test/UnitTest/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/test/UnitTest/BUILD.bazel
@@ -23,6 +23,7 @@
 cc_library(
     name = "LibcUnitTest",
     srcs = [
+        "BazelFilePath.cpp",
         "ExecuteFunctionUnix.cpp",
         "LibcTest.cpp",
         "LibcTestMain.cpp",
@@ -35,6 +36,7 @@
     ],
     deps = [
         ":test_logger",
+        "//libc:__support_c_string",
         "//libc:__support_cpp_bit",
         "//libc:__support_cpp_bitset",
         "//libc:__support_cpp_span",
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/stdio/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/stdio/BUILD.bazel
--- a/utils/bazel/llvm-project-overlay/libc/test/src/stdio/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/stdio/BUILD.bazel
@@ -31,11 +31,11 @@
     libc_function_deps = [
     ],
     deps = [
-      "//libc:printf_string_writer",
-      "//libc:printf_writer",
-      "//libc:printf_core_structs",
-      "//libc:__support_cpp_string_view",
-      "//libc:__support_arg_list",
+        "//libc:__support_arg_list",
+        "//libc:__support_cpp_string_view",
+        "//libc:printf_core_structs",
+        "//libc:printf_string_writer",
+        "//libc:printf_writer",
     ],
 )
 
@@ -45,12 +45,12 @@
     libc_function_deps = [
     ],
     deps = [
-      "//libc:printf_converter",
-      "//libc:printf_string_writer",
-      "//libc:printf_writer",
-      "//libc:printf_core_structs",
-      "//libc:__support_cpp_string_view",
-      "//libc:__support_arg_list",
+        "//libc:__support_arg_list",
+        "//libc:__support_cpp_string_view",
+        "//libc:printf_converter",
+        "//libc:printf_core_structs",
+        "//libc:printf_string_writer",
+        "//libc:printf_writer",
     ],
 )
 
@@ -74,3 +74,19 @@
         "//libc:snprintf",
     ],
 )
+
+libc_test(
+    name = "printf_test",
+    srcs = ["printf_test.cpp"],
+    libc_function_deps = [
+        "//libc:printf",
+    ],
+)
+
+libc_test(
+    name = "fprintf_test",
+    srcs = ["fprintf_test.cpp"],
+    libc_function_deps = [
+        "//libc:fprintf",
+    ],
+)