[PATCH] string: Declare POSIX.1-2024 string functions [BZ #34466]

[Gao Xiang]

From: Xiang Gao <gaoxiang@kylinos.cn>

POSIX.1-2024 adds memmem, strlcpy and strlcat to string.h.
glibc already implements these functions. but their public
declarations are currently only exports by __USE_MISC.
Applications built in POSIX.1-2024 mode with _POSIX_C_SOURCE=
202405L will fail with implicit function declaration errors.

Using existed feature macro to expose the declarations required
by POSIX.1-2024.

Add string/tst-posix2024 to verify strict POSIX.1-2024 header
visibility.

Tested on x86_64 Fedora 42.

The following tests passed without regressions:
  make test t=string/tst-posix2024
  make check subdirs=string
  make check subdirs=conform

Signed-off-by: Xiang Gao <gaoxiang@kylinos.cn>
---
 conform/data/string.h-data |  7 ++++++
 string/Makefile            |  2 ++
 string/string.h            |  6 ++++--
 string/tst-posix2024.c     | 44 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 string/tst-posix2024.c

diff --git a/conform/data/string.h-data b/conform/data/string.h-data
index abc6b12b5d..c9526e06d0 100644
--- a/conform/data/string.h-data
+++ b/conform/data/string.h-data
@@ -13,6 +13,9 @@ function int memcmp (const void*, const void*, size_t)
 function {void*} memcpy (void*, const void*, size_t)
 function {void*} memmove (void*, const void*, size_t)
 function {void*} memset (void*, int, size_t)
+#if defined XOPEN2K24 || defined POSIX2024
+function {void*} memmem (const void*, size_t, const void*, size_t)
+#endif
 #if defined XOPEN2K8 || defined XOPEN2K24 || defined POSIX2008 || defined POSIX2024
 function {char*} stpcpy (char*, const char*)
 function {char*} stpncpy (char*, const char*, size_t)
@@ -38,6 +41,10 @@ function int strerror_r (int, char*, size_t)
 function {char*} strerror_l (int, locale_t)
 #endif
 function size_t strlen (const char*)
+#if defined XOPEN2K24 || defined POSIX2024
+function size_t strlcat (char*, const char*, size_t)
+function size_t strlcpy (char*, const char*, size_t)
+#endif
 function {char*} strncat (char*, const char*, size_t)
 function int strncmp (const char*, const char*, size_t)
 function {char*} strncpy (char*, const char*, size_t)
diff --git a/string/Makefile b/string/Makefile
index aa0b0c2f57..a968994fcb 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -201,6 +201,7 @@ tests := \
   tst-endian \
   tst-inlcall \
   tst-memmove-overflow \
+  tst-posix2024 \
   tst-strerror-fail \
   tst-strfry \
   tst-strlcat \
@@ -270,6 +271,7 @@ CFLAGS-tst-inlcall.c += -fno-builtin
 CFLAGS-tst-xbzero-opt.c += -O3
 CFLAGS-tst-xmemset-opt.c += -O3
 CFLAGS-test-endian-sign-conversion.c += -Werror -Wsign-conversion
+CFLAGS-tst-posix2024.c += -std=c17 -Werror=implicit-function-declaration
 # BZ 21006: Resolve all functions but at least explicit_bzero at startup.
 # Otherwise the test fails on s390x as the memcpy in prepare_test_buffer is
 # done by loading r4 / r5 with the test_pattern and using store multiple
diff --git a/string/string.h b/string/string.h
index 743395b3e3..15959356a2 100644
--- a/string/string.h
+++ b/string/string.h
@@ -414,7 +414,7 @@ extern char *strcasestr (const char *__haystack, const char *__needle)
 # endif
 #endif
 
-#ifdef __USE_MISC
+#if defined __USE_MISC || defined __USE_XOPEN2K24
 /* Find the first occurrence of NEEDLE in HAYSTACK.
    NEEDLE is NEEDLELEN bytes long;
    HAYSTACK is HAYSTACKLEN bytes long.  */
@@ -423,7 +423,9 @@ extern void *memmem (const void *__haystack, size_t __haystacklen,
      __THROW __attribute_pure__ __nonnull ((1, 3))
     __attr_access ((__read_only__, 1, 2))
     __attr_access ((__read_only__, 3, 4));
+#endif
 
+#ifdef __USE_MISC
 /* Copy N bytes of SRC to DEST, return pointer to bytes after the
    last written byte.  */
 extern void *__mempcpy (void *__restrict __dest,
@@ -533,7 +535,7 @@ extern char *stpncpy (char *__restrict __dest,
      __THROW __nonnull ((1, 2));
 #endif
 
-#ifdef __USE_MISC
+#if defined __USE_MISC || defined __USE_XOPEN2K24
 /* Copy at most N - 1 characters from SRC to DEST.  */
 extern size_t strlcpy (char *__restrict __dest,
 		       const char *__restrict __src, size_t __n)
diff --git a/string/tst-posix2024.c b/string/tst-posix2024.c
new file mode 100644
index 0000000000..0e25d0770f
--- /dev/null
+++ b/string/tst-posix2024.c
@@ -0,0 +1,44 @@
+/* Test POSIX.1-2024 <string.h> declarations.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Undo _GNU_SOURCE define before the first public header is included so that
+   this test checks strict POSIX.1-2024 visibility.  */
+
+#undef _GNU_SOURCE
+#define _POSIX_C_SOURCE 202405L
+
+#include <string.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  char buffer[8];
+
+  TEST_COMPARE (strlcpy (buffer, "abc", sizeof buffer), 3);
+  TEST_COMPARE_STRING (buffer, "abc");
+
+  TEST_COMPARE (strlcat (buffer, "defgh", sizeof buffer), 8);
+  TEST_COMPARE_STRING (buffer, "abcdefg");
+
+  TEST_VERIFY (memmem (buffer, strlen (buffer), "cde", 3) == buffer + 2);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.53.0