I have dug deeper into understanding what happens with both versions (method 1 & 2).
If the divisor has a high bit set, then pre[2] is not initialized inside mpn_mod_1_1p_cps(), but it is also not used inside mpn_mod_1_1p() as there are no leading zeroes. In the other scenario, if the high bit is set, pre[2] is set to its appropriate value, and it is used inside mpn_mod_1_1p(). Some commenting could be placed inside /mpn/generic/mod_1.c around lines 248 and 261, or pre[4] can be initialized to all 0's on both 248 & 261: mp_limb_t pre[4] = { 0 }; -Brett Kuntz From: "Vincent Lefevre" <vinc...@vinc17.net> To: "marco bodrato" <marco.bodr...@tutanota.com> Cc: "Brett Kuntz" <ku...@shaw.ca>, gmp-bugs@gmplib.org Sent: Thursday, August 31, 2023 11:06:51 AM Subject: Re: Uninitialized memory bug found in /mpn/generic/mod_1_1.c On 2023-08-31 17:03:12 +0200, marco.bodr...@tutanota.com wrote: > Ciao, > > 31 ago 2023, 16:30 da ku...@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 <vinc...@vinc17.net> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon) _______________________________________________ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs