From b0afb8fe0ff1d87165af9df61501197a06240dda Mon Sep 17 00:00:00 2001
From: Lorenz Kästle <12514511+RincewindsHat@users.noreply.github.com>
Date: Sun, 28 Dec 2025 12:13:40 +0100
Subject: Sync with Gnulib stable-202507 code (a8ac9f9ce5)

---
 gl/m4/strncpy.m4 | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 gl/m4/strncpy.m4

(limited to 'gl/m4/strncpy.m4')

diff --git a/gl/m4/strncpy.m4 b/gl/m4/strncpy.m4
new file mode 100644
index 00000000..57876171
--- /dev/null
+++ b/gl/m4/strncpy.m4
@@ -0,0 +1,94 @@
+# strncpy.m4
+# serial 1
+dnl Copyright (C) 2002-2004, 2009-2025 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+AC_DEFUN_ONCE([gl_FUNC_STRNCPY],
+[
+  AC_REQUIRE([gl_STRING_H_DEFAULTS])
+  AC_REQUIRE([AC_PROG_CC])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+
+  dnl Check for prerequisites for memory fence checks.
+  gl_FUNC_MMAP_ANON
+  AC_CHECK_HEADERS_ONCE([sys/mman.h])
+  AC_CHECK_FUNCS_ONCE([mprotect])
+
+  dnl Detect bug in FreeBSD 15.0 on x86_64:
+  dnl strncpy should not dereference more than n bytes, but always dereferences
+  dnl n+1 bytes if the first n bytes don't contain a NUL byte.
+  dnl Assume that strncpy works on platforms that lack mprotect.
+  AC_CACHE_CHECK([whether strncpy works], [gl_cv_func_strncpy_works],
+    [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <string.h>
+#if HAVE_SYS_MMAN_H
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+#endif
+]GL_MDA_DEFINES],
+[[
+  char *fence = NULL;
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+  {
+    long int pagesize = sysconf (_SC_PAGESIZE);
+    char *two_pages =
+      (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+                     MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    if (two_pages != (char *)(-1)
+        && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+      fence = two_pages + pagesize;
+  }
+#endif
+  if (fence)
+    {
+      char dest[8];
+
+      dest[0] = 'a';
+      dest[1] = 'b';
+      dest[2] = 'c';
+      dest[3] = 'd';
+      dest[4] = 'e';
+      dest[5] = 'f';
+      dest[6] = 'g';
+
+      *(fence - 3) = '7';
+      *(fence - 2) = '2';
+      *(fence - 1) = '9';
+
+      if (strncpy (dest + 1, fence - 3, 3) != dest + 1)
+        return 1;
+      if (dest[0] != 'a')
+        return 2;
+      if (dest[1] != '7' || dest[2] != '2' || dest[3] != '9')
+        return 3;
+      if (dest[4] != 'e')
+        return 4;
+    }
+  return 0;
+]])], [gl_cv_func_strncpy_works=yes], [gl_cv_func_strncpy_works=no],
+       [
+        case "$host_os" in
+                                 # Guess no on FreeBSD.
+          freebsd* | dragonfly*) gl_cv_func_strncpy_works="guessing no" ;;
+                                 # Guess yes on native Windows.
+          mingw* | windows*)     gl_cv_func_strncpy_works="guessing yes" ;;
+                                 # Guess yes otherwise.
+          *)                     gl_cv_func_strncpy_works="guessing yes" ;;
+        esac
+       ])
+    ])
+  case "$gl_cv_func_strncpy_works" in
+    *yes) ;;
+    *) REPLACE_STRNCPY=1 ;;
+  esac
+])
+
+# Prerequisites of lib/strncpy.c.
+AC_DEFUN([gl_PREREQ_STRNCPY], [
+  :
+])
-- 
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