[PATCH] string: Add tests for unique strerror error strings

[Arjun Shankar]

strerror and its variants should return unique strings for each
known/unknown error.  Add tests to verify this for strerror, strerror_r
and strerror_l (for the C locale).

strerror_r is special in that the GNU variant returns "Unknown error"
strings (and only those) in the user supplied buffer, returning
read-only internal strings for known errors.  Additionally test for this
as well.
---
 string/Makefile                 |  3 ++
 string/tst-strerror-strings.c   | 76 +++++++++++++++++++++++++++++++++
 string/tst-strerror_l-strings.c | 38 +++++++++++++++++
 string/tst-strerror_r-strings.c | 48 +++++++++++++++++++++
 4 files changed, 165 insertions(+)
 create mode 100644 string/tst-strerror-strings.c
 create mode 100644 string/tst-strerror_l-strings.c
 create mode 100644 string/tst-strerror_r-strings.c

diff --git a/string/Makefile b/string/Makefile
index c83b195e2e..37719d01a3 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -197,6 +197,9 @@ tests := \
   tst-inlcall \
   tst-memmove-overflow \
   tst-strerror-fail \
+  tst-strerror-strings \
+  tst-strerror_l-strings \
+  tst-strerror_r-strings \
   tst-strfry \
   tst-strlcat \
   tst-strlcat2 \
diff --git a/string/tst-strerror-strings.c b/string/tst-strerror-strings.c
new file mode 100644
index 0000000000..4b53d9d821
--- /dev/null
+++ b/string/tst-strerror-strings.c
@@ -0,0 +1,76 @@
+/* Test that strerror variants return unique strings for each errnum.
+
+   Copyright (C) 2025 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/>.  */
+
+#include <string.h>
+#include <stdlib.h>
+
+#include <support/support.h>
+#include <support/check.h>
+
+static int
+compare_strings (const void *a, const void *b)
+{
+  const char *stra = * (const char **) a;
+  const char *strb = * (const char **) b;
+
+  int ret = strcmp (stra, strb);
+
+  if (!ret)
+    FAIL_EXIT1 ("Found duplicate error strings: \"%s\"\n", stra);
+
+  return ret;
+}
+
+#define NSTRINGS 2049
+
+static int
+do_test (void)
+{
+  char *string[NSTRINGS];
+  /* Convenient indexing for error strings from -1024 to 1024.  */
+  char **err_str = string + 1024;
+
+  unsetenv ("LANGUAGE");
+
+  xsetlocale (LC_ALL, "C");
+
+  for (int i = -1024; i <= 1024; i++)
+    {
+
+#ifdef TEST_STRERROR_VARIANT
+      /* Used for testing strerror_r and strerror_l.  */
+      err_str[i] = TEST_STRERROR_VARIANT (i);
+#else
+      err_str[i] = xstrdup (strerror (i));
+#endif
+
+      /* Negative as well as large positive errnums are unused.  160 allows
+         us to define more errors without needing to update this test.  */
+      int is_unknown_error
+        = (strstr (err_str[i], "Unknown error ") == err_str[i]);
+      TEST_VERIFY_EXIT ((i >= 0 && i < 160) || is_unknown_error);
+    }
+
+  /* We check for and fail on duplicate strings in the comparator.  */
+  qsort (string, NSTRINGS, sizeof (char *), compare_strings);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/string/tst-strerror_l-strings.c b/string/tst-strerror_l-strings.c
new file mode 100644
index 0000000000..186a4b09c7
--- /dev/null
+++ b/string/tst-strerror_l-strings.c
@@ -0,0 +1,38 @@
+/* Test that strerror_l returns unique strings for each errnum.
+
+   Copyright (C) 2025 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/>.  */
+
+#include <stdlib.h>
+#include <string.h>
+#include <support/support.h>
+#include <support/check.h>
+
+static locale_t loc = (locale_t) 0;
+
+/* Wrap strerror_l to be plugged into the equivalent strerror test.  */
+static char *
+wrap_strerror_l (int errnum)
+{
+  if (loc == (locale_t) 0)
+    loc = xnewlocale (LC_ALL_MASK, "C", (locale_t) 0);
+
+  return xstrdup (strerror_l (errnum, loc));
+}
+
+#define TEST_STRERROR_VARIANT wrap_strerror_l
+#include "tst-strerror-strings.c"
diff --git a/string/tst-strerror_r-strings.c b/string/tst-strerror_r-strings.c
new file mode 100644
index 0000000000..feaccfbefb
--- /dev/null
+++ b/string/tst-strerror_r-strings.c
@@ -0,0 +1,48 @@
+/* Test that GNU strerror_r returns unique strings for each errnum.
+
+   Copyright (C) 2025 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/>.  */
+
+#include <stdlib.h>
+#include <string.h>
+#include <support/support.h>
+#include <support/check.h>
+
+/* Wrap strerror_r into a checked variant that can be plugged into the
+   equivalent strerror test.  */
+static char *
+test_and_return_strerror_r (int errnum)
+{
+  char *buf, *ret;
+
+  buf = xmalloc (1024);
+  ret = strerror_r (errnum, buf, 1024);
+
+  /* "Unknown error" strings are returned in user supplied buffer.  */
+  if (strstr (ret, "Unknown error ") == ret)
+    TEST_VERIFY_EXIT (ret == buf);
+  else
+    {
+      TEST_VERIFY_EXIT (ret != buf);
+      free (buf);
+    }
+
+  return ret;
+}
+
+#define TEST_STRERROR_VARIANT test_and_return_strerror_r
+#include "tst-strerror-strings.c"
-- 
2.50.1