Re: [bootstrap-O1] change value type to avoid sprintf buffer size warning

[Georg-Johann Lay <gjl at gcc dot gnu dot org>]

Alexandre Oliva schrieb:
> On Jan  4, 2017, Martin Sebor <msebor@gmail.com> wrote:
>
> > The manual recommends to use a length modifier to constrain the length
> > of output to that of a narrower type:
>
> >   sprintf (xname, "<U%4hx>", ((unsigned short)((uintptr_t)(t) & 0xffff)));
>
> > This should work even without optimization.
>
> It might not work if short happens to be wider than 16 bits, but I guess
> we need not worry about that at -O1.
>
> In stage2 of bootstrap-O1, the code that warns if sprintf might
> overflow its output buffer cannot tell that an unsigned value narrowed
> to 16 bits will fit in 4 bytes with %4x.
>
> Converting the value to 'unsigned short' makes it obvious that it
> fits, at least on machines with 16-bit shorts.

Wouldn't uint16_t be more clear?
And maybe together with PRIx16 instead of "hx"?

Johann

> Regstrapped on x86_64-linux-gnu and i686-linux-gnu.  Ok to install?
>
> for  gcc/c-family/ChangeLog
>
> 	* c-pretty-print.c (pp_c_tree_decl_identifier): Convert 16-bit
> 	value to unsigned short to fit in 4 hex digits without
> 	warnings.
> ---
>  gcc/c-family/c-pretty-print.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c
> index 90428ca..07fdbae 100644
> --- a/gcc/c-family/c-pretty-print.c
> +++ b/gcc/c-family/c-pretty-print.c
> @@ -2400,7 +2400,7 @@ pp_c_tree_decl_identifier (c_pretty_printer *pp, tree t)
>    else
>      {
>        static char xname[8];
> -      sprintf (xname, "<U%4x>", ((unsigned)((uintptr_t)(t) & 0xffff)));
> +      sprintf (xname, "<U%4hx>", ((unsigned short)((uintptr_t)(t) & 0xffff)));
>        name = xname;
>      }
>