[libc] Add strlcpy

[michaelrj]

Overall the patch looks good, I left some comments for the main code but the build system changes are good.

libc/src/string/strlcpy.cpp

24

it doesn't seem like defining a min function is necessary here since it's only used once, I think it would be cleaner to write

size_t len = internal::string_length(src)
size_t n = len < size - 1 ? len : size - 1;

This also helps for the return value.

27

we're trying to keep entrypoints independent, meaning that they shouldn't include each other. In this case using inline_memset(reinterpret_cast<char *>(dst + n), 0, size - n); would be preferred.

28

The return value of strlcpy is "the total length of the string they tried to create. For strlcpy() that means the length of src."
This means that the return value should be len and not n.

[michaelrj]

LGTM

libc/config/darwin/arm/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.memset
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcat
     libc.src.string.strchr
     libc.src.string.strcmp
     libc.src.string.strcpy
     libc.src.string.strcspn
+    libc.src.string.strlcpy
     libc.src.string.strlen
     libc.src.string.strncat
     libc.src.string.strncmp
     libc.src.string.strncpy
     libc.src.string.strnlen
     libc.src.string.strpbrk
     libc.src.string.strrchr
     libc.src.string.strspn

libc/config/linux/aarch64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.memset
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcat
     libc.src.string.strchr
     libc.src.string.strcmp
     libc.src.string.strcpy
     libc.src.string.strcspn
+    libc.src.string.strlcpy
     libc.src.string.strlen
     libc.src.string.strncat
     libc.src.string.strncmp
     libc.src.string.strncpy
     libc.src.string.strnlen
     libc.src.string.strpbrk
     libc.src.string.strrchr
     libc.src.string.strspn

libc/config/linux/api.td

 include "config/public_api.td"
 
+include "spec/bsd_ext.td"
 include "spec/gnu_ext.td"
 include "spec/linux.td"
 include "spec/llvm_libc_ext.td"
 include "spec/posix.td"
 include "spec/stdc.td"
 
 def AssertMacro : MacroDef<"assert"> {
   let Defn = [{

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.memset
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcat
     libc.src.string.strchr
     libc.src.string.strcmp
     libc.src.string.strcpy
     libc.src.string.strcspn
+    libc.src.string.strlcpy
     libc.src.string.strlen
     libc.src.string.strncat
     libc.src.string.strncmp
     libc.src.string.strncpy
     libc.src.string.strnlen
     libc.src.string.strpbrk
     libc.src.string.strrchr
     libc.src.string.strspn

libc/config/windows/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.memset
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcat
     libc.src.string.strchr
     libc.src.string.strcmp
     libc.src.string.strcpy
     libc.src.string.strcspn
+    libc.src.string.strlcpy
     libc.src.string.strlen
     libc.src.string.strncat
     libc.src.string.strncmp
     libc.src.string.strncpy
     libc.src.string.strnlen
     libc.src.string.strpbrk
     libc.src.string.strrchr
     libc.src.string.strspn

libc/spec/bsd_ext.td

+def BsdExtensions : StandardSpec<"BSDExtensions"> {
+  HeaderSpec String = HeaderSpec<
+      "string.h",
+      [], // Macros
+      [], // Types
+      [], // Enumerations
+      [ 
+        FunctionSpec<
+            "strlcpy",
+            RetValSpec<SizeTType>,
+            [ArgSpec<CharPtr>, ArgSpec<ConstCharPtr>, ArgSpec<SizeTType>]
+        >,
+      ]
+  >;
+}

libc/src/string/CMakeLists.txt

HDRS
     strdup.h
   DEPENDS
     .memory_utils.memcpy_implementation
     .string_utils
     libc.include.stdlib
 )
 
 add_entrypoint_object(
+  strlcpy
+  SRCS
+    strlcpy.cpp
+  HDRS
+    strlcpy.h
+  DEPENDS
+    .memory_utils.memcpy_implementation
+    .memory_utils.memset_implementation
+    .string_utils
+    libc.include.string
+)
+
+add_entrypoint_object(
   strlen
   SRCS
     strlen.cpp
   HDRS
     strlen.h
   DEPENDS
     libc.include.string
 )

libc/src/string/strlcpy.h

+//===-- Implementation header for strlcpy -----------------------*- 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_STRLCPY_H
+#define LLVM_LIBC_SRC_STRING_STRLCPY_H
+
+#include <string.h>
+
+namespace __llvm_libc {
+
+size_t strlcpy(char *__restrict dst, const char *__restrict src, size_t size);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_STRLCPY_H

libc/src/string/strlcpy.cpp

+//===-- Implementation of strlcpy -----------------------------------------===//
+//
+// 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/strlcpy.h"
+#include "src/string/bzero.h"
+#include "src/string/memory_utils/memcpy_implementations.h"
+#include "src/string/memory_utils/memset_implementations.h"
+#include "src/string/string_utils.h"
+
+#include "src/__support/common.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(size_t, strlcpy,
+                   (char *__restrict dst, const char *__restrict src,
+                    size_t size)) {
+  size_t len = internal::string_length(src);
+  if (!size)
+    return len;
+  size_t n = len < size - 1 ? len : size - 1;
+  inline_memcpy(dst, src, n);
+  inline_memset(dst + n, 0, size - n);
+  return len;
+}
+
+} // namespace __llvm_libc

libc/test/src/string/CMakeLists.txt

add_libc_unittest(
   SRCS
     strdup_test.cpp
   DEPENDS
     libc.include.stdlib
     libc.src.string.strdup
 )
 
 add_libc_unittest(
+  strlcpy_test
+  SUITE
+    libc_string_unittests
+  SRCS
+    strlcpy_test.cpp
+  DEPENDS
+    libc.src.string.strlcpy
+)
+
+add_libc_unittest(
   strlen_test
   SUITE
     libc_string_unittests
   SRCS
     strlen_test.cpp
   DEPENDS
     libc.src.string.strlen
 )

libc/test/src/string/strlcpy_test.cpp

+//===-- Unittests for strlcpy ---------------------------------------------===//
+//
+// 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/strlcpy.h"
+#include "utils/UnitTest/Test.h"
+#include <stdlib.h>
+
+TEST(LlvmLibcStrlcpyTest, TooBig) {
+  const char *str = "abc";
+  char buf[2];
+  EXPECT_EQ(__llvm_libc::strlcpy(buf, str, 2), 3ul);
+  EXPECT_STREQ(buf, "a");
+
+  EXPECT_EQ(__llvm_libc::strlcpy(nullptr, str, 0), 3ul);
+}
+
+TEST(LlvmLibcStrlcpyTest, Smaller) {
+  const char *str = "abc";
+  char buf[7]{"111111"};
+
+  EXPECT_EQ(__llvm_libc::strlcpy(buf, str, 7), 3ul);
+  EXPECT_STREQ(buf, "abc");
+  for (const char *p = buf + 3; p < buf + 7; p++)
+    EXPECT_EQ(*p, '\0');
+}