Enhance test coverage for strnlen, wcsnlen

This commit adds string/test-strnlen-nonarray and
wcsmbs/test-wcsnlen-nonarray.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

string/Makefile

@@ -184,6 +184,7 @@ tests := \
   test-strncpy \
   test-strndup \
   test-strnlen \
+  test-strnlen-nonarray \
   test-strpbrk \
   test-strrchr \
   test-strspn \

string/test-Xnlen-nonarray.c

@@ -0,0 +1,133 @@
+/* Test non-array inputs to string length functions.
+   Copyright (C) 2024 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/>.  */
+
+/* This skeleton file is included from string/test-strnlen-nonarray.c
+   and wcsmbs/test-wcsnlen-nonarray.c to test that reading of the array
+   stops at the first null character.
+
+   TEST_IDENTIFIER must be the test function identifier.  TEST_NAME is
+   the same as a string.
+
+   CHAR must be defined as the character type.  */
+
+#include <array_length.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/next_to_fault.h>
+#include <support/test-driver.h>
+#include <sys/param.h>
+#include <unistd.h>
+
+typedef __typeof (TEST_IDENTIFIER) *proto_t;
+
+#define TEST_MAIN
+#include "test-string.h"
+
+IMPL (TEST_IDENTIFIER, 1)
+
+static int
+test_main (void)
+{
+  enum { buffer_length = 256 };
+  TEST_VERIFY_EXIT (sysconf (_SC_PAGESIZE) >= buffer_length);
+
+  test_init ();
+
+  /* Buffer layout: There are a_count 'A' character followed by
+     zero_count null character, for a total of buffer_length
+     character:
+
+     AAAAA...AAAAA 00000 ... 00000 (unmapped page follows)
+     \           / \             /
+       (a_count)     (zero_count)
+       \___ (buffer_length) ___/
+          ^
+          |
+          start_offset
+
+    The buffer length does not change, but a_count (and thus _zero)
+    and start_offset vary.
+
+    If start_offset == buffer_length, only 0 is a valid length
+    argument.  The result is 0.
+
+    Otherwwise, if zero_count > 0 (if there a null characters in the
+    buffer), then any length argument is valid.  If start_offset <
+    a_count (i.e., there is a non-null character at start_offset), the
+    result is the minimum of a_count - start_offset and the length
+    argument.  Otherwise the result is 0.
+
+    Otherwise, there are no null characters before the unmapped page.
+    The length argument must not be greater than buffer_length -
+    start_offset, and the result is the length argument.  */
+
+  struct support_next_to_fault ntf
+    = support_next_to_fault_allocate (buffer_length * sizeof (CHAR));
+  CHAR *buffer = (CHAR *) ntf.buffer;
+
+  FOR_EACH_IMPL (impl, 0)
+    {
+      printf ("info: testing %s\n", impl->name);
+      for (size_t i = 0; i < buffer_length; ++i)
+        buffer[i] = 'A';
+
+      for (int zero_count = 0; zero_count <= buffer_length; ++zero_count)
+        {
+          if (zero_count > 0)
+            buffer[buffer_length - zero_count] = 0;
+          int a_count = buffer_length - zero_count;
+          for (int start_offset = 0; start_offset <= buffer_length;
+               ++start_offset)
+            {
+              CHAR *start_pointer = buffer + start_offset;
+              if (start_offset == buffer_length)
+                TEST_COMPARE (CALL (impl, buffer + start_offset, 0), 0);
+              else if (zero_count > 0)
+                for (int length_argument = 0;
+                     length_argument <= 2 * buffer_length;
+                     ++length_argument)
+                  {
+                    if (test_verbose)
+                      printf ("zero_count=%d a_count=%d start_offset=%d"
+                              " length_argument=%d\n",
+                              zero_count, a_count, start_offset,
+                              length_argument);
+                    if (start_offset < a_count)
+                      TEST_COMPARE (CALL (impl, start_pointer, length_argument),
+                                    MIN (a_count - start_offset,
+                                         length_argument));
+                    else
+                      TEST_COMPARE (CALL (impl, start_pointer, length_argument),
+                                    0);
+                  }
+              else
+                for (int length_argument = 0;
+                     length_argument <= buffer_length - start_offset;
+                     ++length_argument)
+                  TEST_COMPARE (CALL (impl, start_pointer, length_argument),
+                                length_argument);
+            }
+        }
+    }
+
+  support_next_to_fault_free (&ntf);
+
+  return 0;
+}
+
+#include <support/test-driver.c>

string/test-strnlen-nonarray.c

@@ -0,0 +1,4 @@
+#define TEST_IDENTIFIER strnlen
+#define TEST_NAME "strnlen"
+typedef char CHAR;
+#include "test-Xnlen-nonarray.c"

wcsmbs/Makefile

@@ -160,6 +160,7 @@ tests := \
   test-wcsncmp \
   test-wcsncpy \
   test-wcsnlen \
+  test-wcsnlen-nonarray \
   test-wcspbrk \
   test-wcsrchr \
   test-wcsspn \

wcsmbs/test-wcsnlen-nonarray.c

@@ -0,0 +1,5 @@
+#include <wchar.h>
+#define TEST_IDENTIFIER wcsnlen
+#define TEST_NAME "wcsnlen"
+typedef wchar_t CHAR;
+#include "../string/test-Xnlen-nonarray.c"