From: Phillip Wood <phillip.wood123@gmail.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
Jeff King <peff@peff.net>
Subject: Re: [PATCH 5/7] xdiff: use GALLOC_GROW(), not XDL_ALLOC_GROW()
Date: Wed, 13 Jul 2022 10:09:33 +0100 [thread overview]
Message-ID: <e86cac3b-4e05-be20-41d8-ed5006463556@gmail.com> (raw)
In-Reply-To: <220711.861qur9ays.gmgdl@evledraar.gmail.com>
Hi Ævar
On 11/07/2022 11:48, Ævar Arnfjörð Bjarmason wrote:
>
> On Mon, Jul 11 2022, Phillip Wood wrote:
>
>> Hi Ævar
>>
>> On 08/07/2022 15:20, Ævar Arnfjörð Bjarmason wrote:
>>> Replace the recently introduced XDL_ALLOC_GROW() with invocations of
>>> the GALLOC_GROW() from git-shared-util.h.
>>> As this change shows the macro + function indirection of
>>> XDL_ALLOC_GROW() is something we needed only because the two callsites
>>> we used it in wanted to use it as an expression, and we thus had to
>>> pass the "sizeof" down.
>>> Let's just check the value afterwards instead, which allows us to
>>> use
>>> the shared macro, we can also remove xdl_reallo(), this was its last
>>> user.
>>
>> I don't think this expression->statement change is an
>> improvement.
>
> I think the use-as-statement is prettier too, but I think the uglyness
> of having to pass down the sizeof() & re-implementing the macro version
> of the alloc-or-die variant outweights that.
I think this is partly a choice between prioritizing ease of
implementation or ease of use for callers.
>> This change also removes the overflow checks that are
>> present in XDL_ALLOC_GROW()[...]
>
> We end up calling st_mult(), which does that overflow check. Do you mean
> that the POC shimmy layer I showed in another reply for libgit2 doesn't
> have an st_mult() that detects overflows?
I was referring to
#define alloc_nr(x) (((x)+16)*3/2)
in cache.h. XDL_ALLOC_GROW() detects overflows when growing the number
of items as well as when calculating the number of bytes to allocate.
> That's true, but as noted downthread of that we can & could ship that as
> part of the shimmy layer, but that's unrelated to this change.
>
> In your pre-image you use LONG_MAX instead of UINTMAX_MAX & I don't see
> (but maybe I haven't looked at it carefully enough) how it does the same
> dying on overflows. Doesn't it just fall back to LONG_MAX?
It does not die on overflow as we want to return errors rather than die
in the xdiff code. It uses long to match the existing code.
> Part of this is that it's not clear to me from your commit(s) why you
> need to rewrite alloc_nr() and rewrite (or drop?) st_mult().
So that we don't die on overflow and so that the xdiff code is self
contained.
I'm a bit disappointed that this patch seems to have been written
without really taking the time to understand exactly what the code it is
replacing is doing.
Best Wishes
Phillip
>> and fails to free the old allocation when
>> realloc() fails. It is not a like for like replacement.
>
> Yes, we should have a free() there. Wel spotted. But again, doing that
> as part of the "gently" branch seems preferrable to have duplicate
> versions for expression (non-fatal) v.s. statement (fatal) variants.
next prev parent reply other threads:[~2022-07-13 9:09 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-29 15:25 [PATCH 0/3] xdiff: introduce memory allocation macros Phillip Wood via GitGitGadget
2022-06-29 15:25 ` [PATCH 1/3] xdiff: introduce XDL_ALLOC_ARRAY() Phillip Wood via GitGitGadget
2022-06-29 15:25 ` [PATCH 2/3] xdiff: introduce XDL_CALLOC_ARRAY() Phillip Wood via GitGitGadget
2022-06-30 18:17 ` Junio C Hamano
2022-07-06 13:17 ` Phillip Wood
2022-06-29 15:25 ` [PATCH 3/3] xdiff: introduce XDL_ALLOC_GROW() Phillip Wood via GitGitGadget
2022-06-30 10:54 ` Ævar Arnfjörð Bjarmason
2022-06-30 12:03 ` Phillip Wood
2022-06-30 12:38 ` Phillip Wood
2022-06-30 13:25 ` Ævar Arnfjörð Bjarmason
2022-07-06 13:23 ` Phillip Wood
2022-07-07 11:17 ` Ævar Arnfjörð Bjarmason
2022-07-08 9:35 ` Phillip Wood
2022-07-08 14:20 ` [PATCH 0/7] xdiff: use standard alloc macros, share them via git-shared-util.h Ævar Arnfjörð Bjarmason
2022-07-08 14:20 ` [PATCH 1/7] xdiff: simplify freeing patterns around xdl_free_env() Ævar Arnfjörð Bjarmason
2022-07-08 14:20 ` [PATCH 2/7] git-shared-util.h: move "shared" allocation utilities here Ævar Arnfjörð Bjarmason
2022-07-08 14:20 ` [PATCH 3/7] git-shared-util.h: add G*() versions of *ALLOC_*() Ævar Arnfjörð Bjarmason
2022-07-11 10:06 ` Phillip Wood
2022-07-08 14:20 ` [PATCH 4/7] xdiff: use G[C]ALLOC_ARRAY(), not XDL_CALLOC_ARRAY() Ævar Arnfjörð Bjarmason
2022-07-11 10:10 ` Phillip Wood
2022-07-08 14:20 ` [PATCH 5/7] xdiff: use GALLOC_GROW(), not XDL_ALLOC_GROW() Ævar Arnfjörð Bjarmason
2022-07-11 10:13 ` Phillip Wood
2022-07-11 10:48 ` Ævar Arnfjörð Bjarmason
2022-07-13 9:09 ` Phillip Wood [this message]
2022-07-13 10:48 ` Ævar Arnfjörð Bjarmason
2022-07-13 13:21 ` Phillip Wood
2022-07-08 14:20 ` [PATCH 6/7] xdiff: remove xdl_malloc() wrapper, use malloc(), not xmalloc() Ævar Arnfjörð Bjarmason
2022-07-08 17:42 ` Phillip Wood
2022-07-08 21:44 ` Ævar Arnfjörð Bjarmason
2022-07-08 19:35 ` Jeff King
2022-07-08 21:47 ` Ævar Arnfjörð Bjarmason
2022-07-11 9:33 ` Jeff King
2022-07-08 14:20 ` [PATCH 7/7] xdiff: remove xdl_free(), use free() instead Ævar Arnfjörð Bjarmason
2022-07-08 17:51 ` Phillip Wood
2022-07-08 21:26 ` Ævar Arnfjörð Bjarmason
2022-07-11 9:26 ` Phillip Wood
2022-07-11 9:54 ` Phillip Wood
2022-07-11 10:02 ` Ævar Arnfjörð Bjarmason
2022-07-13 13:00 ` Phillip Wood
2022-07-13 13:18 ` Ævar Arnfjörð Bjarmason
2022-06-30 18:32 ` [PATCH 3/3] xdiff: introduce XDL_ALLOC_GROW() Junio C Hamano
2022-07-06 13:14 ` Phillip Wood
2022-06-30 10:46 ` [PATCH 0/3] xdiff: introduce memory allocation macros Ævar Arnfjörð Bjarmason
2022-07-08 16:25 ` [PATCH v2 0/4] " Phillip Wood via GitGitGadget
2022-07-08 16:25 ` [PATCH v2 1/4] xdiff: introduce XDL_ALLOC_ARRAY() Phillip Wood via GitGitGadget
2022-07-08 16:25 ` [PATCH v2 2/4] xdiff: introduce xdl_calloc Phillip Wood via GitGitGadget
2022-07-08 16:25 ` [PATCH v2 3/4] xdiff: introduce XDL_CALLOC_ARRAY() Phillip Wood via GitGitGadget
2022-07-08 16:25 ` [PATCH v2 4/4] xdiff: introduce XDL_ALLOC_GROW() Phillip Wood via GitGitGadget
2022-07-08 22:17 ` Ævar Arnfjörð Bjarmason
2022-07-11 10:00 ` Phillip Wood
2022-07-12 7:19 ` Jeff King
2022-07-13 9:38 ` Phillip Wood
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