Re: SIGSEGV on isprime

[Ján Jančár <johny@neuromancer.sk>]

On 15/07/18 15:05, Karim Belabas wrote:
> * Bill Allombert [2018-07-11 17:25]:
>> On Wed, Jul 11, 2018 at 04:48:24PM +0200, Ján Jančár wrote:
>>>>> I have now tested:
>>>>>
>>>>> --enable-tls --kernel=none      --> works
>>>>> --enable-tls --kernel=none-gmp  --> SEGVs!
>>>>> --enalbe-tls --kernel=auto-none --> works
>>
>> My guess is that there is a buffer overflow in the function
>> red_montgomery in the file src/kernel/gmp/mp.c which only
>> cause a SEGV when the stack ends on a page boundary.
> 
> Not exactly a buffer overflow but an off-by-1 error causing us to read
> one word beyond the boundary of the modulus 'N'. In this particular
> case, N happens to be the first object on the PARI stack and we read
> 1 word in unallocated memory [ and disregard its value, making the bug
> very hard to spot ].
> 
> I believe the problem is solved in 'master' HEAD.
> 
> Cheers,
> 
>     K.B.
> --
> Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
> Universite de Bordeaux         Fax: (+33) (0)5 40 00 21 23
> 351, cours de la Liberation    http://www.math.u-bordeaux.fr/~kbelabas/
> F-33405 Talence (France)       http://pari.math.u-bordeaux.fr/  [PARI/GP]
> `
> 

Great, thanks for solving this!

Cheers,
-- 
Jan
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