localedef: Use initializer for flexible array member [BZ #24950]

struct charseq used a zero-length array instead of a flexible array
member.  This required a strange construct to initialize struct
charseq objects, and GCC 10 warns about that:

cc1: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
In file included from programs/repertoire.h:24,
                 from programs/localedef.h:32,
                 from programs/ld-ctype.c:35:
programs/charmap.h:63:17: note: destination object declared here
   63 |   unsigned char bytes[0];
      |                 ^~~~~
cc1: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
programs/charmap.h:63:17: note: destination object declared here
cc1: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
programs/charmap.h:63:17: note: destination object declared here
cc1: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
programs/charmap.h:63:17: note: destination object declared here

The change makes the object physically const, but it is not expected
to be modified.

3 files changed, 15 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index 67ec991785..e215c4a717 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2019-09-03  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #24950]
+	* locale/programs/charmap.h (struct charseq): Turn bytes into a
+	flexible array member.
+	* locale/programs/ld-ctype.c (ctype_finish): Use initializer for
+	replace.
+
 2019-09-02  Florian Weimer  <fweimer@redhat.com>
 
 	* misc/tst-mntent-autofs.c: New file.
diff --git a/locale/programs/charmap.h b/locale/programs/charmap.h
index 870a9e9577..70db330d29 100644
--- a/locale/programs/charmap.h
+++ b/locale/programs/charmap.h
@@ -60,7 +60,7 @@ struct charseq
   const char *name;
   uint32_t ucs4;
   int nbytes;
-  unsigned char bytes[0];
+  unsigned char bytes[];
 };
 
 
diff --git a/locale/programs/ld-ctype.c b/locale/programs/ld-ctype.c
index cfc9c43fd5..9123f64a56 100644
--- a/locale/programs/ld-ctype.c
+++ b/locale/programs/ld-ctype.c
@@ -842,8 +842,6 @@ no input digits defined and none of the standard names in the charmap"));
   for (cnt = 0; cnt < 10; ++cnt)
     if (ctype->mboutdigits[cnt] == NULL)
       {
-	static struct charseq replace[2];
-
 	if (!warned)
 	  {
 	    record_error (0, 0, _("\
@@ -851,10 +849,12 @@ not all characters used in `outdigit' are available in the charmap"));
 	    warned = 1;
 	  }
 
-	replace[0].nbytes = 1;
-	replace[0].bytes[0] = '?';
-	replace[0].bytes[1] = '\0';
-	ctype->mboutdigits[cnt] = &replace[0];
+	static const struct charseq replace =
+	  {
+	     .nbytes = 1,
+	     .bytes = "?",
+	  };
+	ctype->mboutdigits[cnt] = (struct charseq *) &replace;
       }
 
   warned = 0;