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From: ZheNing Hu <>
To: Junio C Hamano <>
Cc: ZheNing Hu via GitGitGadget <>,
	Git List <>,
	Johannes Schindelin <>
Subject: Re: [PATCH v4] [GSOC] ref-filter: fix read invalid union member bug
Date: Tue, 11 May 2021 14:28:32 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <xmqqcztyovf7.fsf@gitster.g>

Junio C Hamano <> 于2021年5月11日周二 上午10:29写道:
> "ZheNing Hu via GitGitGadget" <> writes:
> >     Change from last version:
> >     Prove that the bug may appear when using %(color) atom. And add
> >     corresponding test for it.
> >      ++test_expect_success '%(color:#aa22ac) must success' '
> s/success/succeed/
> But more importantly, I am not sure how this is supposed to
> demonstrate existing breakage around the %(push).  Did you mean to
> use %(push) instead of %(refname) or something?

Ah, I don’t think this scene of damage is related to using %(push)
or %(refname).

We are just in the process of using `populate_value()`, if the atom we
specify meets the following conditions, then the condition of
atom->u.remote_ref.push!=0 will be established.

1. The atom that triggers the bug , its "if" condition order must after
"if (atom->u.remote_ref.push)", such as %(refname) or %(worktreepath),
they can be executed correctly because their order is before "push".

2. The member size in used_atom.u corresponding to the atom must
larger than 17 bytes, because the offset of "u.remote_ref.push" in
"u.remote_ref" is 17, the satisfied atoms are only "%(color)" and
 "%(contents)", their corresponding members are u.color and u.contents.

3. We happen to be able to fill in the 17th position of these structures,
 which makes atom->u.remote_ref.push not equal to 0 established.

So this kind of bug is not related to %(push), an atom that satisfies
the above conditions will make `if (atom->u.remote_ref.push)` be true.
then execute the program logic related to `%(push)`.

Now, we only have `%(color)` can trigger it "sometime",
It is unpredictable to fill in the 17th byte of used_atom.u.color,
so we cannot track all the atoms related to this bug.

git for-each-ref --format="%(color:#aa22ac)%(refname)"
git for-each-ref --format="%(color:#aa22ad)%(refname)"

will trigger the bug.

git for-each-ref --format="%(color:#aa22ae)%(refname)"
git for-each-ref --format="%(color:#aa22af)%(refname)"

will not trigger the bug.

In other words, we cannot use a perfect test set to cover all broken.
So now `%(color:#aa22ac)` is enough for explain the problem of this bug.

ZheNing Hu

  reply	other threads:[~2021-05-11  6:28 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-05 15:31 [PATCH] [GSOC] ref-filter: solve bugs caused by enumeration ZheNing Hu via GitGitGadget
2021-05-06  1:53 ` Junio C Hamano
2021-05-06  5:02   ` ZheNing Hu
2021-05-06  5:35     ` Junio C Hamano
2021-05-06 10:39       ` ZheNing Hu
2021-05-06 11:20         ` Junio C Hamano
2021-05-06 11:52           ` ZheNing Hu
2021-05-06 21:20             ` Junio C Hamano
2021-05-07  4:32               ` ZheNing Hu
2021-05-07  4:49                 ` Junio C Hamano
2021-05-07  5:09                   ` ZheNing Hu
2021-05-06 16:31 ` [PATCH v2] [GSOC] ref-filter: fix read invalid union member bug ZheNing Hu via GitGitGadget
2021-05-08 15:26   ` [PATCH v3] " ZheNing Hu via GitGitGadget
2021-05-10  7:21     ` Junio C Hamano
2021-05-10 12:35       ` ZheNing Hu
2021-05-10  7:27     ` Junio C Hamano
2021-05-10 12:51       ` ZheNing Hu
2021-05-10 15:01     ` [PATCH v4] " ZheNing Hu via GitGitGadget
2021-05-11  2:29       ` Junio C Hamano
2021-05-11  6:28         ` ZheNing Hu [this message]
2021-05-11  9:30           ` Junio C Hamano
2021-05-11 11:47             ` ZheNing Hu
2021-05-11 13:12               ` Junio C Hamano
2021-05-11 13:31                 ` ZheNing Hu
2021-05-11 15:35       ` [PATCH v5] " ZheNing Hu via GitGitGadget
2021-05-12  1:36         ` Junio C Hamano
2021-05-12 10:37           ` ZheNing Hu
2021-05-12 12:12         ` [PATCH v6] " ZheNing Hu via GitGitGadget
2021-05-12 23:24           ` Junio C Hamano
2021-05-13  9:29             ` ZheNing Hu
2021-05-13 15:13           ` [PATCH v7] " ZheNing Hu via GitGitGadget

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