Re: ToT glibc build problem with ToT GCC

[Florian Weimer <fweimer at redhat dot com>]

* Szabolcs Nagy:

> On 30/08/2019 17:18, Florian Weimer wrote:
>> 
>> localedef: Use initializer for flexible array member [BZ #24950]
>> 
>
> i would mention that you put the struct in .rodata,
> that is a non-obvious change.

Please see below.

> i'm fine with using gcc extension for the initializer.
> i think the union solution is a bit safer though.
> either way, it would be nice to fix this build error.

I don't think this is a GCC extension.  I believe it's part of C99.

Thanks,
Florian

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.

2019-08-30  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.

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;