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

[Brett Kuntz]

> Looking at mpn/generic/mod_1_1.c, 
> if MOD_1_1P_METHOD == 1, the value[2] in the array is always set and always used; 
> if MOD_1_1P_METHOD == 2, the value[2] is set only if cnt!=0, and it is used only if cnt!=0. 
> There are also some assembler code implementations, each one with its couple of functions. 

I concluded the same just now. 

-Brett Kuntz 


From: "marco bodrato" <marco.bodrato at tutanota.com> 
To: "Vincent Lefevre" <vincent at vinc17.net> 
Cc: "Brett Kuntz" <kuntz at shaw.ca>, gmp-bugs at gmplib.org 
Sent: Thursday, August 31, 2023 12:33:46 PM 
Subject: Re: Uninitialized memory bug found in /mpn/generic/mod_1_1.c 

Ciao, 

31 ago 2023, 18:06 da vincent at vinc17.net: 



I don't think that this is sufficient for the test. 
The code Brett mentioned is for MOD_1_1P_METHOD = 2. 




The code Brett mentioned is mixed, I fear. 
Looking at mpn/generic/mod_1_1.c, 
if MOD_1_1P_METHOD == 1, the value[2] in the array is always set and always used; 
if MOD_1_1P_METHOD == 2, the value[2] is set only if cnt!=0, and it is used only if cnt!=0. 
There are also some assembler code implementations, each one with its couple of functions. 


BQ_BEGIN

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 */ 

BQ_END


Not enough, MOD_1_1P_METHOD may be defined by gmp-mparam.h 
One should also check how MOD_1N_TO_MOD_1_1_THRESHOLD interact with the tests. 

BQ_BEGIN

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

BQ_END



BQ_BEGIN

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

BQ_END

Actually it is possible to trigger this, if you put it in the wrong place, I mean, outside the branch actually using the value... but it is not interesting. 

Ĝis, 
Marco