[libc] Add strdup implementation.

[cgyurgyik]

Summary

Adds strdup implementation. Memcpy is more efficient since we don't need to check if the character is the null terminator with each iteration.

[cgyurgyik]

Remove strcmp from strdup testing.

[cgyurgyik]

Add length variable to call strlen once.

[cgyurgyik]

Add header for size_t.

[abrachet]

libc/src/string/strdup.cpp

18

We can't use new unfortunately. Even if operator new was a completely free standing allocator which didn't depend on libc functions we may not provide, operator new[] is not guaranteed to be free-able by free. This function has to wait for malloc

[cgyurgyik]

libc/src/string/strdup.cpp

18

Ok thanks. I'll close this for now then.

[cgyurgyik]

Malloc not available yet.

[tschuett]

Add a redirector for malloc/free as a temporary solution?

[cgyurgyik]

In D82376#2109451, @tschuett wrote:

Add a redirector for malloc/free as a temporary solution?

I just saw this. Can you clarify? I'm not sure how this would be done.

[tschuett]

See below:
https://github.com/llvm/llvm-project/blob/master/libc/docs/redirectors.rst

[cgyurgyik]

In D82376#2138227, @tschuett wrote:

See below:
https://github.com/llvm/llvm-project/blob/master/libc/docs/redirectors.rst

Thanks.

[tschuett]

There was a redirector for the round function:
https://reviews.llvm.org/D69020

[sivachandra]

In D82376#2140137, @tschuett wrote:

There was a redirector for the round function:
https://reviews.llvm.org/D69020

Thanks, @tschuett!
@cgyurgyik, That patch has an example of course. In case you decide to add redirectors for free and malloc, feel free to ask questions.

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     # string.h entrypoints
     libc.src.string.bzero
     libc.src.string.memcpy
     libc.src.string.memset
     libc.src.string.strcpy
     libc.src.string.strcat
     libc.src.string.strlen
     libc.src.string.strcmp
+    libc.src.string.strdup
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.mmap
     libc.src.sys.mman.munmap
 
     # threads.h entrypoints
     libc.src.threads.call_once
     libc.src.threads.mtx_init

libc/src/string/CMakeLists.txt

add_entrypoint_object(
   SRCS
     strcmp.cpp
   HDRS
     strcmp.h
   DEPENDS
     libc.include.string
 )
 
+add_entrypoint_object(
+  strdup
+  SRCS
+    strdup.cpp
+  HDRS
+    strdup.h
+  DEPENDS
+    .memcpy
+    .strlen
+    libc.include.string
+)
+
 # Helper to define a function with multiple implementations
 # - Computes flags to satisfy required/rejected features and arch,
 # - Declares an entry point,
 # - Attach the REQUIRE_CPU_FEATURES property to the target,
 # - Add the fully qualified target to `${name}_implementations` global property for tests.
 function(add_implementation name impl_name)
   cmake_parse_arguments(
     "ADD_IMPL"

libc/src/string/strdup.h

+//===-- Implementation header for strdup ------------------------*- 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_STRING_STRDUP_H
+#define LLVM_LIBC_SRC_STRING_STRDUP_H
+
+#include "include/string.h"
+
+namespace __llvm_libc {
+
+char *strdup(const char *src);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_STRDUP_H

libc/src/string/strdup.cpp

+//===-- Implementation of strdup ------------------------------------------===//
+//
+// 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/string/strdup.h"
+#include "src/string/memcpy.h"
+#include "src/string/strlen.h"
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+char *LLVM_LIBC_ENTRYPOINT(strdup)(const char *src) {
+  const size_t length = __llvm_libc::strlen(s) + 1;
+  char *duplicate = new char[length];
+  if (!duplicate)
+    return NULL;
+  return reinterpret_cast<char *>(memcpy(duplicate, s, length));
+}
+
+} // namespace __llvm_libc

libc/test/src/string/CMakeLists.txt

add_libc_unittest(
   SUITE
     libc_string_unittests
   SRCS
     strcmp_test.cpp
   DEPENDS
     libc.src.string.strcmp
 )
 
+add_libc_unittest(
+  strdup_test
+  SUITE
+    libc_string_unittests
+  SRCS
+    strdup_test.cpp
+  DEPENDS
+    libc.src.string.strdup
+)
+
 # Tests all implementations that can run on the host.
 function(add_libc_multi_impl_test name)
   get_property(fq_implementations GLOBAL PROPERTY ${name}_implementations)
   foreach(fq_config_name IN LISTS fq_implementations)
     get_target_property(required_cpu_features ${fq_config_name} REQUIRE_CPU_FEATURES)
     host_supports(can_run "${required_cpu_features}")
     if(can_run)
       add_libc_unittest(

libc/test/src/string/strdup_test.cpp

+//===-- Unittests for strdup ----------------------------------------------===//
+//
+// 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/string/strdup.h"
+
+TEST(StrDupTest, NullTerminatorIsIncluded) {
+  const char *s = "foobar";
+  const char *dup = __llvm_libc::strdup(s);
+  ASSERT_STREQ(s, dup);
+}
+
+TEST(StrDupTest, DuplicateOfEmptyStringShouldBeEmptyString) {
+  const char *empty = "";
+  const char *dup = __llvm_libc::strdup(empty);
+  ASSERT_STREQ(empty, dup);
+}
+
+TEST(StrDupTest, DuplicateShouldBeEqualToOriginalString) {
+  const char *s = "abcd1234";
+  const char *dup = __llvm_libc::strdup(s);
+  ASSERT_STREQ(s, dup);
+}