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In-Reply-To: <33dfd007-ac28-44a5-acee-cec4b381e854n@googlegroups.com>
From: Antoine Riard <antoine.riard@gmail.com>
Date: Thu, 4 Jul 2024 14:20:57 +0100
Message-ID: <CALZpt+Fs1U5f3S6_tR7AFfEMEkgBPSp3OaNEq+eqYoCSSYXD7g@mail.gmail.com>
Subject: Re: [bitcoindev] Re: Great Consensus Cleanup Revival
To: Eric Voskuil <eric@voskuil.org>
Cc: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
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> I assume this function lets you search for an element starting in the
middle of a single-linked list (the middle because you could call
`ft_list_find(&p-next, data_ref)` where `p` points to any element in the
> middle of the list, including possibly the last item in the list, in
which case the loop body wouldn't run). If so, I don't think this does
what's intended. This actually unlinks (and memory-leaks) elements up to >
where the match is found. I think you want to advance `start_list` this way
(I didn't test this):

Note the usage of a pointer to pointer so the correct way to call the code
is : `pointer_t * list_ptr ; list_ptr =3D first_list_element ;
ft_list_find(list_ptr, data_rf, cmp);`.
This is correct that if you point to the last item in the list, the loop
body wouldn't run (which is the expected behavior). When there is a match,
the pointer `*start_list` takes as value the memory address of the next
element in the list, the contained structure pointer is not changed. The
code has been tested a while back, though it's indeed clearer if a typedef
`pointer_t` for list is fully given:

```
typedef struct                 s_list
{
                         void     *content;
                         size_t  content_size;
                         struct  s_list. *next;
}                                      pointer_t
```

> This is why we don't use C - unsafe, unclear, unnecessary.

Actually, I think libbitcoin is using its own maintained fork of secp256k1,
which is written in C.
For sure, I wouldn't recommend using C across a whole codebase as it's not
memory-safe (euphemism) though it's still un-match if you wish to
understand low-level memory management in hot paths.
It can be easier to use C++ or Rust, though it doesn't mean it will be as
(a) perf optimal and (b) hardened against side-channels.

I have not read in detail the last Eric's email on the whole caching
identity in case of invalidity discussion, though I'll do so.

Best,
Antoine


Le jeu. 4 juil. 2024 =C3=A0 00:57, Eric Voskuil <eric@voskuil.org> a =C3=A9=
crit :

> This is why we don't use C - unsafe, unclear, unnecessary.
>
> e
>
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<div dir=3D"ltr">&gt; I assume this function lets you search for an element=
 starting in the middle of a single-linked list (the middle because you cou=
ld call `ft_list_find(&amp;p-next, data_ref)` where `p` points to any eleme=
nt in the<div>&gt; middle of the list, including possibly the last item in =
the list, in which case the loop body wouldn&#39;t run). If so, I don&#39;t=
 think this does what&#39;s intended. This actually unlinks (and memory-lea=
ks) elements up to &gt; where the match is found. I think you want to advan=
ce `start_list` this way (I didn&#39;t test this):<div><br></div><div>Note =
the usage of a pointer to pointer so the correct way to call the code is : =
`pointer_t * list_ptr ; list_ptr =3D first_list_element ; ft_list_find(list=
_ptr, data_rf, cmp);`.</div><div>This is correct that if you point to the l=
ast item in the list, the loop body wouldn&#39;t run (which is the expected=
 behavior). When there is a match, the pointer `*start_list` takes as value=
 the memory address of the next element in the list, the contained structur=
e pointer is not changed. The code has been tested a while back, though it&=
#39;s indeed clearer if a typedef `pointer_t` for list is fully given:=C2=
=A0</div></div><div><br></div><div>```</div><div>typedef struct =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 s_list</div><div>{</div><div>=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0void =C2=A0 =C2=A0 *content;</div><div>=C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0si=
ze_t =C2=A0content_size;</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0struct =C2=A0s_list. *n=
ext;</div><div>} =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0pointer_t</div><div>```</div><div><br></div><div>&gt; This is why we don=
&#39;t use C - unsafe, unclear, unnecessary.<br></div><div><br></div><div>A=
ctually, I think libbitcoin is using its own maintained fork of secp256k1, =
which is written in C.</div><div>For sure, I wouldn&#39;t recommend using C=
 across a whole codebase as it&#39;s not memory-safe (euphemism) though it&=
#39;s still un-match if you wish to understand low-level memory management =
in hot paths.</div><div>It can be easier to use C++ or Rust, though it does=
n&#39;t mean it will be as (a) perf optimal and (b) hardened against side-c=
hannels.</div><div><br></div><div>I have not read in detail the last Eric&#=
39;s email on the whole caching identity in case of invalidity discussion, =
though I&#39;ll do so.</div><div><br></div><div>Best,</div><div>Antoine</di=
v><div><br></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" clas=
s=3D"gmail_attr">Le=C2=A0jeu. 4 juil. 2024 =C3=A0=C2=A000:57, Eric Voskuil =
&lt;<a href=3D"mailto:eric@voskuil.org">eric@voskuil.org</a>&gt; a =C3=A9cr=
it=C2=A0:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0p=
x 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color=
:rgb(204,204,204);padding-left:1ex">This is why we don&#39;t use C - unsafe=
, unclear, unnecessary.<div><br></div><div>e</div>

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