Re: [PATCH 1/6] locale: prevent maybe-uninitialized errors with -Os [BZ #19444]

[Carlos O'Donell <carlos@redhat.com>]

On Wed, Sep 21, 2022 at 10:51:03AM -0300, Adhemerval Zanella via Libc-alpha wrote:
> From: Martin Jansa <Martin.Jansa@gmail.com>
> 
> Fixes following error when building  with -Os:
> | In file included from strcoll_l.c:43:
> | strcoll_l.c: In function '__strcoll_l':
> | ../locale/weight.h:31:26: error: 'seq2.back_us' may be used
> uninitialized in this function [-Werror=maybe-uninitialized]
> |    int_fast32_t i = table[*(*cpp)++];
> |                           ^~~~~~~~~
> | strcoll_l.c:304:18: note: 'seq2.back_us' was declared here
> |    coll_seq seq1, seq2;
> |                   ^~~~
> | In file included from strcoll_l.c:43:
> | ../locale/weight.h:31:26: error: 'seq1.back_us' may be used
> uninitialized in this function [-Werror=maybe-uninitialized]
> |    int_fast32_t i = table[*(*cpp)++];
> |                           ^~~~~~~~~
> | strcoll_l.c:304:12: note: 'seq1.back_us' was declared here
> |    coll_seq seq1, seq2;
> |             ^~~~

LGTM.

No regresions on x86_64.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  locale/weight.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/locale/weight.h b/locale/weight.h
> index 8be2d220f8..4a4d5aa6b2 100644
> --- a/locale/weight.h
> +++ b/locale/weight.h
> @@ -27,7 +27,14 @@ findidx (const int32_t *table,
>  	 const unsigned char *extra,
>  	 const unsigned char **cpp, size_t len)
>  {
> +  /* With GCC 8 when compiling with -Os the compiler warns that
> +     seq1.back_us and seq2.back_us might be used uninitialized.
> +     This uninitialized use is impossible for the same reason
> +     as described in comments in locale/weightwc.h.  */

OK. Agreed.

> +  DIAG_PUSH_NEEDS_COMMENT;
> +  DIAG_IGNORE_Os_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
>    int32_t i = table[*(*cpp)++];
> +  DIAG_POP_NEEDS_COMMENT;
>    const unsigned char *cp;
>    const unsigned char *usrc;
>  
> -- 
> 2.34.1
>