From ludo at gnu.org  Mon Jan  4 10:59:59 2021
From: ludo at gnu.org (=?utf-8?Q?Ludovic_Court=C3=A8s?=)
Date: Mon, 04 Jan 2021 10:59:59 +0100
Subject: [gnutls-help] Bug#964284: guile-gnutls: update to use guile 3.0
In-Reply-To: <87v9cjxupe.fsf-ueno@gnu.org> (Daiki Ueno's message of "Wed, 30
 Dec 2020 14:57:33 +0100")
References: <87v9j2204s.fsf@ponder> <877dpymybw.fsf@yucca>
 <87czzm2ehb.fsf@gnu.org> <87lfe83heg.fsf@trouble.defaultvalue.org>
 <87a6uoutgn.fsf@gnu.org> <87blem41jz.fsf@gnu.org>
 <87v9cjxupe.fsf-ueno@gnu.org>
Message-ID: <87ble5xbs0.fsf@gnu.org>

Hi Daiki,

Daiki Ueno <ueno at gnu.org> skribis:

> Ludovic Court?s <ludo at gnu.org> writes:
>
>> This is because Guile >= 3.0.1 and >= 2.2.7 changes the GMP allocation
>> functions such that they go through libgc?.  As a result, libgc may
>> reuse that memory when it becomes unreachable from its point of view; in
>> this case, since GnuTLS structures are not scanned by libgc, libgc
>> doesn?t ?see? pointers to those bignums and thus considers they are no
>> longer reachable.
>
> That's interesting, though I might not follow completely.
>
>>   ? In Guile-GnuTLS, arrange so that GnuTLS allocations are made through
>>     libgc.  Unfortunately, ?gnutls_global_set_mem_functions? was
>>     deprecated in GnuTLS 3.3.0 so this doesn?t look like an option.
>
> GnuTLS doesn't call mp_set_memory_functions, so even if it is possible,
> I doubt that it would affect the current behavior.

What happens currently is that data structures allocated by GnuTLS are
not scanned by the GC; thus, when those data structures refer to an
?mpz_t?, the GC doesn?t ?see? those references.

If we could arrange so that GnuTLS allocates via libgc, those ?mpz_t?
references would become visible to the GC, which would solve this issue.

Would it be an option?

> On the other hand, if GnuTLS (or Nettle) internally allocates an
> mpz_t, it should be done using the libgc-backed allocator set by Guile
> and the pointers should be reachable until it is no longer, if I
> understand correctly.  Therefore, I suspect that there might be some
> code that confuses libgc to track the pointers; one thing that comes
> to my mind is a manual copy of mpz_t values:
> https://gitlab.com/gnutls/gnutls/-/blob/master/lib/nettle/pk.c#L141
>

> If you replace memcpy with mpz_init_set, does it work?

I tried the patch below but it doesn?t help.

Thanks for taking a look!

Ludo?.

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From ametzler at bebt.de  Sat Jan 16 18:27:30 2021
From: ametzler at bebt.de (Andreas Metzler)
Date: Sat, 16 Jan 2021 18:27:30 +0100
Subject: [gnutls-help] Bug#964284: Bug#964284: guile-gnutls: update to
 use guile 3.0
In-Reply-To: <87v9cjxupe.fsf-ueno@gnu.org>
References: <87v9j2204s.fsf@ponder> <877dpymybw.fsf@yucca>
 <87czzm2ehb.fsf@gnu.org> <87lfe83heg.fsf@trouble.defaultvalue.org>
 <87a6uoutgn.fsf@gnu.org> <87blem41jz.fsf@gnu.org>
 <87v9j2204s.fsf@ponder> <87v9cjxupe.fsf-ueno@gnu.org>
Message-ID: <YAMiAqG4E7fguSpI@argenau.bebt.de>

On 2020-12-30 Daiki Ueno <ueno at gnu.org> wrote:
> Ludovic Court?s <ludo at gnu.org> writes:
[...]
> >   ? In Guile-GnuTLS, arrange so that GnuTLS allocations are made through
> >     libgc.  Unfortunately, ?gnutls_global_set_mem_functions? was
> >     deprecated in GnuTLS 3.3.0 so this doesn?t look like an option.

> GnuTLS doesn't call mp_set_memory_functions, so even if it is possible,
> I doubt that it would affect the current behavior.  On the other hand,
> if GnuTLS (or Nettle) internally allocates an mpz_t, it should be done
> using the libgc-backed allocator set by Guile and the pointers should be
> reachable until it is no longer, if I understand correctly.  Therefore,
> I suspect that there might be some code that confuses libgc to track the
> pointers; one thing that comes to my mind is a manual copy of mpz_t
> values:
> https://gitlab.com/gnutls/gnutls/-/blob/master/lib/nettle/pk.c#L141

> If you replace memcpy with mpz_init_set, does it work?

Stupid question: That suggestion is about using mpz_init_set instead of
memcpy for all of these initializations, not just for the specific one
in the specific function?

cu Andreas
-- 
`What a good friend you are to him, Dr. Maturin. His other friends are
so grateful to you.'
`I sew his ears on from time to time, sure'