[PATCH] locale: Avoid zero-length array in _nl_category_names [BZ #24962]

[Florian Weimer <fweimer at redhat dot com>]

(Martin, can you give this a test using GCC 10?  I don't expect any
issues because the zero-length array is completely gone.  The patch
passed testing on x86_64-linux-gnu without regressions, but with GCC 9.)

The union wrapper is unnecessary because C allows to read any object
as a sequence of chars.

2019-09-05  Florian Weimer  <fweimer@redhat.com>

	[BZ #24962]
	* locale/localeinfo.h (_nl_category_names): Remove union wrapper.
	(_nl_category_names_get): New function.
	* intl/dcigettext.c (category_to_name): Call it.
	* locale/findlocale.c (_nl_find_locale): Likewise.
	* intl/loadlocale.c (_nl_load_locale): Likewise.
	* locale/newlocale.c (__newlocale): Likewise.
	* locale/setlocale.c (_nl_category_names): Adjust definition.
	(_nl_category_name_idxs): Likewise.
	(new_composite_name): Call _nl_category_names_get.
	(setlocale): Likewise.

diff --git a/intl/dcigettext.c b/intl/dcigettext.c
index 4df93e2a8e..11f3749457 100644
--- a/intl/dcigettext.c
+++ b/intl/dcigettext.c
@@ -360,8 +360,7 @@ static const char *guess_category_value (int category,
 
 #ifdef _LIBC
 # include "../locale/localeinfo.h"
-# define category_to_name(category) \
-  _nl_category_names.str + _nl_category_name_idxs[category]
+# define category_to_name(category) _nl_category_names_get (category)
 #else
 static const char *category_to_name (int category);
 #endif
diff --git a/locale/findlocale.c b/locale/findlocale.c
index 9af605bd64..28b0226265 100644
--- a/locale/findlocale.c
+++ b/locale/findlocale.c
@@ -118,8 +118,7 @@ _nl_find_locale (const char *locale_path, size_t locale_path_len,
 	 variables.  */
       cloc_name = getenv ("LC_ALL");
       if (!name_present (cloc_name))
-	cloc_name = getenv (_nl_category_names.str
-			    + _nl_category_name_idxs[category]);
+	cloc_name = getenv (_nl_category_names_get (category));
       if (!name_present (cloc_name))
 	cloc_name = getenv ("LANG");
       if (!name_present (cloc_name))
@@ -207,8 +206,7 @@ _nl_find_locale (const char *locale_path, size_t locale_path_len,
 				    locale_path, locale_path_len, mask,
 				    language, territory, codeset,
 				    normalized_codeset, modifier,
-				    _nl_category_names.str
-				    + _nl_category_name_idxs[category], 0);
+				    _nl_category_names_get (category), 0);
 
   if (locale_file == NULL)
     {
@@ -218,8 +216,7 @@ _nl_find_locale (const char *locale_path, size_t locale_path_len,
 					locale_path, locale_path_len, mask,
 					language, territory, codeset,
 					normalized_codeset, modifier,
-					_nl_category_names.str
-					+ _nl_category_name_idxs[category], 1);
+					_nl_category_names_get (category), 1);
       if (locale_file == NULL)
 	/* This means we are out of core.  */
 	return NULL;
diff --git a/locale/loadlocale.c b/locale/loadlocale.c
index 571c94e1de..ff578f6416 100644
--- a/locale/loadlocale.c
+++ b/locale/loadlocale.c
@@ -199,8 +199,7 @@ _nl_load_locale (struct loaded_l10nfile *file, int category)
       newp = (char *) alloca (filenamelen
 			      + 5 + _nl_category_name_sizes[category] + 1);
       __mempcpy (__mempcpy (__mempcpy (newp, file->filename, filenamelen),
-			    "/SYS_", 5),
-		 _nl_category_names.str + _nl_category_name_idxs[category],
+			    "/SYS_", 5), _nl_category_names_get (category),
 		 _nl_category_name_sizes[category] + 1);
 
       fd = __open_nocancel (newp, O_RDONLY | O_CLOEXEC);
diff --git a/locale/localeinfo.h b/locale/localeinfo.h
index 7c1cc3eecb..0e2a0d7e49 100644
--- a/locale/localeinfo.h
+++ b/locale/localeinfo.h
@@ -183,23 +183,29 @@ enum
 #define _ISCTYPE(c, desc) \
   (((((const uint32_t *) (desc)) - 8)[(c) >> 5] >> ((c) & 0x1f)) & 1)
 
-/* Category name handling variables.  */
+/* Category name handling variables.  Concatenate all the strings in a
+   single object to minimize relocations.  Individual strings can be
+   accessed using _nl_category_names.  */
 #define CATNAMEMF(line) CATNAMEMF1 (line)
 #define CATNAMEMF1(line) str##line
-extern const union catnamestr_t
+extern const struct catnamestr_t
 {
-  struct
-  {
 #define DEFINE_CATEGORY(category, category_name, items, a) \
-    char CATNAMEMF (__LINE__)[sizeof (category_name)];
+  char CATNAMEMF (__LINE__)[sizeof (category_name)];
 #include "categories.def"
 #undef DEFINE_CATEGORY
-  };
-  char str[0];
 } _nl_category_names attribute_hidden;
 extern const uint8_t _nl_category_name_idxs[__LC_LAST] attribute_hidden;
 extern const uint8_t _nl_category_name_sizes[__LC_LAST] attribute_hidden;
 
+/* Return the name of the category INDEX, which must be nonnegative
+   and less than _LC_LAST.  */
+static inline const char *
+_nl_category_names_get (int index)
+{
+  return (const char *) &_nl_category_names + _nl_category_name_idxs[index];
+}
+
 /* Name of the standard locales.  */
 extern const char _nl_C_name[] attribute_hidden;
 extern const char _nl_POSIX_name[] attribute_hidden;
diff --git a/locale/newlocale.c b/locale/newlocale.c
index 8c5960a45d..561244245b 100644
--- a/locale/newlocale.c
+++ b/locale/newlocale.c
@@ -131,8 +131,7 @@ __newlocale (int category_mask, const char *locale, locale_t base)
 	  for (cnt = 0; cnt < __LC_LAST; ++cnt)
 	    if (cnt != LC_ALL
 		&& (size_t) (cp - np) == _nl_category_name_sizes[cnt]
-		&& memcmp (np, (_nl_category_names.str
-				+ _nl_category_name_idxs[cnt]), cp - np) == 0)
+		&& memcmp (np, (_nl_category_names_get (cnt)), cp - np) == 0)
 	      break;
 
 	  if (cnt == __LC_LAST)
diff --git a/locale/setlocale.c b/locale/setlocale.c
index 9bd35454b9..264a1ecba7 100644
--- a/locale/setlocale.c
+++ b/locale/setlocale.c
@@ -65,20 +65,18 @@ static char *const _nl_current_used[] =
 
 
 /* Define an array of category names (also the environment variable names).  */
-const union catnamestr_t _nl_category_names attribute_hidden =
+const struct catnamestr_t _nl_category_names attribute_hidden =
   {
-    {
 #define DEFINE_CATEGORY(category, category_name, items, a) \
-      category_name,
+    category_name,
 #include "categories.def"
 #undef DEFINE_CATEGORY
-    }
   };
 
 const uint8_t _nl_category_name_idxs[__LC_LAST] attribute_hidden =
   {
 #define DEFINE_CATEGORY(category, category_name, items, a) \
-    [category] = offsetof (union catnamestr_t, CATNAMEMF (__LINE__)),
+    [category] = offsetof (struct catnamestr_t, CATNAMEMF (__LINE__)),
 #include "categories.def"
 #undef DEFINE_CATEGORY
   };
@@ -180,7 +178,7 @@ new_composite_name (int category, const char *newnames[__LC_LAST])
 	const char *name = (category == LC_ALL ? newnames[i]
 			    : category == i ? newnames[0]
 			    : _nl_global_locale.__names[i]);
-	p = __stpcpy (p, _nl_category_names.str + _nl_category_name_idxs[i]);
+	p = __stpcpy (p, _nl_category_names_get (i));
 	*p++ = '=';
 	p = __stpcpy (p, name);
 	*p++ = ';';
@@ -298,8 +296,7 @@ setlocale (int category, const char *locale)
 	      for (cnt = 0; cnt < __LC_LAST; ++cnt)
 		if (cnt != LC_ALL
 		    && (size_t) (cp - np) == _nl_category_name_sizes[cnt]
-		    && (memcmp (np, (_nl_category_names.str
-				     + _nl_category_name_idxs[cnt]), cp - np)
+		    && (memcmp (np, (_nl_category_names_get (cnt)), cp - np)
 			== 0))
 		  break;