Re: ToT glibc build problem with ToT GCC

[Szabolcs Nagy <Szabolcs dot Nagy at arm dot com>]

On 03/09/2019 11:12, Florian Weimer wrote:
> * 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.

iso c has this example:

http://port70.net/~nsz/c/c11/n1570.html#6.7.2.1p21

so the initializer relies on a gcc extension.

> 
> 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;
>