Uninitialized memory bug found in /mpn/generic/mod_1_1.c

[Vincent Lefevre]

On 2023-08-31 17:03:12 +0200, marco.bodrato at tutanota.com wrote:
> Ciao,
> 
> 31 ago 2023, 16:30 da kuntz at shaw.ca:
> 
> > 1) Edit line 248 mpn/generic/mp_limb_t pre[4]; into:
> >
> ~/src/gmp$ hg diff mpn/generic/
> diff -r 3ac5afa36be5 mpn/generic/mod_1.c
> --- a/mpn/generic/mod_1.c       Wed Nov 02 13:48:37 2022 +0100
> +++ b/mpn/generic/mod_1.c       Thu Aug 31 16:46:35 2023 +0200
> @@ -245,7 +245,7 @@
>         }
>        else
>         {
> -         mp_limb_t pre[4];
> +         mp_limb_t pre[4] = {-1, -1, -1, -1};
>           mpn_mod_1_1p_cps (pre, b);
>           return mpn_mod_1_1p (ap, n, b, pre);
>         }
> 

I don't think that this is sufficient for the test.
The code Brett mentioned is for MOD_1_1P_METHOD = 2.
So, in mpn/generic/mod_1_1.c, I also changed

# define MOD_1_1P_METHOD 1    /* need to make sure this is 2 for asm testing */

to

# define MOD_1_1P_METHOD 2    /* need to make sure this is 2 for asm testing */

and at the beginning of

mpn_mod_1_1p (mp_srcptr ap, mp_size_t n, mp_limb_t b, const mp_limb_t bmodb[4])

I added

  ASSERT (bmodb[2] != -1);

(if bmodb[2] is not set, this would fail).

Then I configured with

  ./configure --disable-assembly --enable-assert

to enable the code and the assert, then "make" and "make check".

But even with that, I don't get any failure.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
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